13Swords

Thanks Old83, nice words are always appreciated.

Sorry about the reading load on the post and N/P on any re-suggestions, I'll take 'em! No idea on what the vac reading is as I do not have a vac guage worth a darn to use. I will say though that with the engine running, I can put my hand over the carb throat & it sucks it down violently at about 1/2 an inch away, & it's got a fair amount of resistance to me pulling my hand off. Makes me think the vac side is better than good.

Checked PCV baffle when I had the cover off to adjust valves; present & undamaged. PCV Valve & Grommet are new, less than 50 miles on them. Valve cover gasket, rubber disc plugs under hold-down nuts & half-moon gaskets all have less than 200 miles on them; & they pass the visual & feel tests. Wires, plugs, cap, rotor and DISTRIBUTOR are all NEW. All have been checked, spec'ed, etc.

EXCELLENT advice on welding cast iron sir! Everything you said is dead on the money. Only reason my repair didn't work was a lack of access to an oxy setup; not enuff heat from a MAAP Gas torch to do it right. Local welding shops took a look at it & constantly found excuses for why they didn't even want to try to braze it up for me. Chickens.

Thanks also for the last compliment. The knowledge has been very hard earned, and only recently to boot! Just shows you can still learn if your mind is open to it.

I have an update on the "fix" & will post that up separately. Thanks again for the input!!!

13Swords

So, I got the exhaust manifold ordered from YodaJim, took about a week to get here via UPS Ground (CO to FL). I love learning new things but not this time. It turns out that 20R exhaust manifolds for the 79 to 81 model years have the double outlet on them like the 22R manifolds do, and that is what they sent. The 78 and earlier has the single outlet. Ratzen Fratzen. I did tell them it was the single outlet, & it was even written on my receipt, but apparently there was a mixup on their end & they sent me the wrong one. I can't afford to buy the double outlet downpipe to make it work; if I could, I also would have gotten the brand new aftermarket manifold that is out there:

https://images-na.ssl-images-amazon....1Hw5RE9R7L.jpg

Argh. Anywho, I got Jim back on the phone and he said he'd make it right & he did. Mucho props to him for being a man of honor. We sent the wrong one back, he refunded our shipping cost & sent the right one at his own expense. Integrity, what a novel concept nowadays.

So it took me 3 hours to get the manifold swap out done (why does this thing fight me at every small turn & opportunity?) Got it fired up this morning for tuning & testing. That's where the fun started all over again.

Engine compartment a lot less noisy now, so there's 1 good thing. Checked all around the manifold with a heater hose to me ear, other end near manifold, no leaks heard anywhere. GOOD. Ran fine on high idle, kicked down to low idle OK, if a bit high; adjusted low idle. I can now get it to idle @ 850 but it STILL won't stay there, still inconsistant. You rev it & it comes back to 1000 to 1100 & varies between those two points (not quickly btw). Try some more revs; when letting go of the throttle & coming back to idle it's STILL popping out the tailpipe!

Tried adjusting the mixture from stock setting of 2 & 1/2 turns up to give it more gas @ idle. Got up to 1200 RPM at about 4 turns out. Adjusted idle back down, still wandering, slowly. Still popping on decel after rev. Took mixture all the way out to 6 turns before it made any difference on the popping problem. Still there most of the time, just a ton milder. The extra idle fuel doesn't seem to affect the engine idle character at all; weird. Rechecked timing; was slightly advanced (10 degrees) so reset to 8 degrees per tune up specs. Didn't seem to make much difference in what I was hearing.

Test drive. Took it around the neighborhood, including my favorite back road where two 60 MPH blasts were done for a mile. Throttle response good, power good, no hesitation or stumble. Letting off the gas in gear occasional mild pop from tailpipe, doesn't do it every time. Brake stalling problem is still there and occasional (stalling under braking to a stop in neutral, no load on engine, wants to stall out). Noticed temp gauge running cooler than before, right on 1/4 where it always used to be. The previous "electric stall-out problem" did NOT happen even once this time. This was when the truck was stalling out almost like someone turned the key off; didn't happen this time. Total run time test & drive about 30 minutes.

So what am I left with? Everyone and his uncle sez that the tailpipe popping is unburned fuel hitting the air at the end of the tailpipe, and is a symptom of an exhaust leak. Thot I just fixed all the exhaust leaks? Lord knows I can't find any in the system anywhere now, & my cylinder head is NOT cracked either (but my own head MAY be after all of this )

Mebbe the desmog guys are wrong about something (in case you didn't know, I desmogged the truck completely during this process. They say run the vac advance to the dist. & the brake booster if you have one (mine is disconnected & port on carb is tightly capped), & cap off everything else on a stock carb & it will be fine. Me don't think so. Thinking the throttle positioner/dashpot needs to be hooked up to vacuum. Apparently what this little gem does is slow the closing rate of the throttle butterflys at the base of the carb when you let off the gas pedal. Why does that matter? Without it, the butterflys slam closed when you let off the gas, causing an immediate rich condition (closed butterflys act like closed valves and don't let the air get in, insta-rich condition). That would explain the extra unburned fuel in the exhaust now wouldn't it? With the device hooked up to a vac source, it "cushions" the closing, slowing the rate of closing so they don't slam shut. It's an abrupt closing compared to a more gradual closing.

On several forums covering all kinds of makes, I've been finding this below or a version of it over and over:

"If you are stopped at a red traffic light, and the guy to your left takes off, and so do you. Then you quickly realize your light is still red, and in a fraction of a second, you take your foot off the gas and stomp the brake. This will almost always cause the engine to die... UNLESS YOU HAVE A DAMPENER (dashpot) to lower the throttle the last 5%,slowly."

With this in mind I tried something. Start the truck back up, grab the throttle lever underhood, rev it up & completely let go so it snaps the throttle closed. I got a pop almost every time. Then tried it again but kept my finger on the lever, providing a VERY small amount of pressure on the lever as it closed. Almost every time, no popping. I'm a human dashpot! Well, since my arm won't reach under the hood while I'm driving & it's hard to see thru the hood while driving, I'm going to go get some vac line and hook that sucker back up & see what happens.

Heck, it might even cure part of the "brake stalling" problem.

Also, that problem could be related to low gas in the tank. I've never had more than 3 or 4 gallons max in it during all of this, as I didn't want our wonderful modern miracle gas to attract water or go bad in less than 30 days. Hard braking causes gas to rush forward (where the fuel pump is in the tank) but then of course it goes backwards (physics - action/reaction) starving the fuel pump. Makes sense as when I brake hard, it doesn't try to stall right away, it's always 2 or three seconds after I hit the brake. Moderate braking sometimes causes it to act like it wants to stall, but almost always recovers in a few seconds. Could be.

Last thot is that mebbe I have a sticking exhaust valve at low engine speeds. There seems to be a small, inconsistent "miss" @ idle, but no miss at all under any throttle. All ignition parts are new so that's not it. If a valve was bent I'd sure hear it & the miss would be there in most if not all ranges of engine speeds, right? Mebbe since I haven't run it "normally" in almost 9 months (just test runs & test drives) it's just some "schmutz" built up in a valve guide, carbon build up on a seat or somesuch. Could well be. A few longer, high duration rips might solve that problem. Time will tell.

So a few more small things to do to solve these annoyances. At least the truck is driveable now & I'm not afraid of hurting the engine with a lean condition. AND no more CO poisoning from underhood. BIG plus! I'll post another update if anything relevant happens. Thanks again to all for reading & responding.

13Swords

Just an update that I will try to keep as direct as possible.

I decided to see about possible sticky valves by doing a motor flush. I used GUNK Motor Medic. You run the engine up to full operating temp, drain out 1 quart of oil, then add the quart of Motor Medic to your oil. Run @ idle ONLY for 5 minutes; no driving or revving! Just let it idle. After 5 minutes shut it down & drain the oil. Do an oil change as usual from there.

My oil was running fairly clean as it was, since I cleaned out the inside of the timing cover (timing set job 2 years ago) and valve cover (valve adjustment 3 months ago). Those two moves alone kept the oil a lot cleaner during the 6 month interval that I change oil. When I drained it after the Motor Medic treatment, the oil was a lot darker, but you could still see thru it a lil bit. I also noticed that while it was idling the engine got progressively quieter & actually picked up a little idle speed w/no adjustment from me. The exhaust was also a lot more consistent & even; no missing or popping, just an even lower rumble. After getting the fresh oil & filter in it, it ran GREAT!
Quiet, very even, and noticed there was even less "shaking" of the motor (yes I have checked my motor mounts, they're fine). Also, almost NO valve noise at all!

I gotta say I was very impressed with the result & would recommend the stuff. I've run 270 miles since & the engine is still running very well, & the oil on the dipstick looks like it just came out of the bottle! Even the oil pressure seems to have improved. I don't have a gauge on it, but it used to take a full 2 seconds for the oil light to go off after start-up before. Now, I can't even count "one-one-thousand", the oil light goes out that quick after start-up.

Other problems:

1. I'm still having a weird, intermittent backfiring/tailpipe popping/stalling issue. I've triple checked all of the electrics, including the connectors; all good, and I have cleaned everything to bright copper. No loose or dirty connections I can find anywhere. My next thing to attack on this is the throttle linkages. The '78 & before had a mechanical rod system with ball joint rod ends. PIC here:

There are 2 of these on a rod, connecting the gas pedal linkage to the carb linkage. Rod threads into the open end shown, with a jamnut to hold it there (kinda like the double nut trick). The rod looks original so it's 39 years old with who knows what mileage & use. There is some slop in the ball joints; possibly the balls or the sockets (or both!) have worn, which could cause the rod to sort of "flop over" & cause binding between the spring clip & the nut. Or the slop in the joint is just causing issues.

After a bunch of research the best I could find was one from Dorman # 115-002, $9.50 each from O'Reilly's; best price I could find out there. Some guys on Ebay wanted up to $30 a piece for these! No Thanks. Got two joints on order, got some threaded rod & jamnuts from the hardware store, so I'll be building my own. Would love to use the original rod but the threads are metric.

2. Gas Tank/Fuel Sender:

The gas tank has been it's own headache. Finally thot I got it sealed up good with PC-7 Epoxy Paste, but it didn't last. Third different thing I tried; nothing worked. Lots of pinholes in the tank above the flange on the front side from leaves & schmutz rotting, creating acids & eating the steel over the years. So I can only run a max of 8 gallons at a time or it leaks; not as bad as before, but still leaks. Will have to save up the pennies and try Yota Jim to see if he has a solid used tank. You cannot get a new replacement tank for 78 & before, of course. And, it looks like the 79 to 85 tanks, which of course you CAN get new, won't work without a fair amounts of modification. UGH.

The fuel sender was another problem. My original stopped working when the truck decided to take a vacation. Turned out the resistor wire windings inside were broken. I tried a VDO "universal" replacement sender (again, of course no one sells an exact replacement), that came with it's own problems. My gas gauge works on 3 ohms resistance full, 90 ohms empty. Of course this is exactly backwards from almost everything else out there; even Toyota changed it to 3 ohms EMPTY & 90 ohms full somewhere around 82 I think. The supplier I got the sender from (Summit) said to just mount it upside down on the fuel pump stem. TONS of engineering mind-bending on that one & I won't bore you with it, BUT, I have to say, IT DOESN'T WORK RIGHT, despite sounding simple.

The sender itself doesn't seem to want to work right, no matter what you do to it, AND, it's only gotten worse since I put it in. I put 8 gallons of gas in a 17 gallon tank, I expect to see near half full. NOPE. Would read barely under 1/4. Last time I got 8 gallons in the tank, it would barely read above E. NO good. Even worse I actually ran out of gas 2 days ago; I've NEVER run this truck out of gas in the 18 years I've had it! So, obviously, I'VE had it with this. I can't recommend this sender to anyone. It's sold for $30 to $40 most places on the web & is called VDO brand in some places. Looks like this:

Stay away unless you enjoy migraines, depression, and long walks to the gas station/convenience store to buy overpriced 1 gallon gas cans.

So with that said, I am now going to attempt to fix my old sender, by rewinding the resistance wire with new wire. I can afford $5 for the wire; I can't afford $120 to have it "professionally" done.

This has been written up on Yotatech before but I couldn't find it. If you want to know what I'm talking about, just search Google for "rewinding a fuel sender" & look at the posting on it on The Samba (an early VW Bug/Bus forum that's been around a loooong time). It's a great write-up & explains everything in good detail. I'll also put a link here:
http://www.thesamba.com/vw/forum/viewtopic.php?t=380693

Only good thing I can think of is that I can cannibalize the new one for parts if needed. Gad I HATE waste!

Otherwise, truck is running great most of the time, and at speeds above 25, it's bloody lovely! just that partial throttle/idle problem to solve. I'll post the results of the throttle linkage rebuild so you'll know if that was the problem or not. Thanks again for reading.

13Swords

Taking them in order from previous post -

* I got the ball joint rod ends from O'reileys plus some matching threaded rod and fabricated up a new throttle linkage rod. After installing, it actually solved 95% of the idle & stalling problems, thank gawd! Was beginning to think I'd never get it solved! Idle is good & consistant @ 850 as it should be 95% of the time, which leads me to -

Pointers/Hints - I bought the 1/4" ball joint rod ends; should have gotten the 3/16" ones instead. They aren't as big around and still have enuff beef to get the job done. There are two rubber cushions w/steel sleeves in them, as a part of the big black hinge on the firewall that is a part of the linkage system. Of course, you cannot get those rubber pieces, so I swapped in some neoprene washers, stacked up to the right height. Only problem was, the top one or two were flopping over @ the edge closest to the rod end, & with the rod end being 1/16" bigger, there was interference & binding. Cut the edges off with a sharp knife, no more binding! This was an inconsistent problem that defied diagnosis; that is, until I slowed down and actually looked at the darn thing. Lesson to me: take your time and check everything again. New parts do NOT guarantee that it's going to work OK.

* Fuel Sender - Ran out of gas AGAIN since the last post.
Enuff is enuff, on the phone to Yoda Jim for a replacement tank, and online to get the resistance wire to fix my old sender. It was a long, tedious, pains-taking job, but I got it working again! I got the wire online for $4 delivered; 10 feet of it, from Jacobs Online. Just google them, you'll find them. My sender took a bit over 4 feet of wire. I got 36 gauge Nichrome 60 wire, which works OK. I followed the advice from The Samba article (see last post) and it all worked out OK. Sorry no pics of the finished sender, but do have a video of it on Youtube; just search "the13thsword" on there to find it.

Got the new/old tank from Yoda Jim, pulled the leaky one (much easier now since I've done it 3 times in the last year! ), swapped over the filler, changed out the sender, put it all back in. Everything working fine with no leaks!

Filled her up to the brim with gas today, which is something I've NEVER been able to do in the 19 years I've owned her. Here's proof that the sender is working:



Gotta love that!

Pointers/Tips - I should prolly have gone with 34 gauge wire rather than the 36 gauge; it would have made wrapping the wire a lot easier & with a lil tweaking, the ohm range would have come out OK.
DO NOT BELIEVE FOR A SECOND that you can take the "universal" fuel sender & invert it & that it will work; IT WON'T. These things are wound in such a way that they are more sensitive on the "empty" side, and the "full" side is less sensitive. Turning it upside down caused me to have less "discrimination" or "calibration" @ the "empty" side, where I needed it most. That's why I ran out of gas twice; gauge still showed a reserve when there was nothing left. Bah. I'd like to get my hands on the fool that told me you could do that & that it would be fine.

Yoda Jim's is the BOMB. Recommended to everyone! The tank was $100 plus shipping, & came out of a '77 Chinook camper; low miles & no abuse on the tank! Couldn't have asked for better!

That takes care of it for now. I will consider this thread closed, unless someone writes with a question or comment. On to the clutch next. Always something more......

Marikate Workman

Hi, I see this post is 6 months old or so, and I'm wondering whether the idle/stalling problem was resolved. My '76 Chinook is really putting me through it, I'm
not in quite as deep as you are with ordering ceiling fan parts etc but am paying someone to do the work and it's not getting better with anything tried so far. Fixed an exhaust manifold leak, new muffler and tailpipe, has been at a carburetor specialist twice now and he has even resoldered little joints on circuit boards and replaced tiny springs and valves and just really gone over the whole vac system looking for leaks or problems and the thing is still stalling at red lights and sometimes turns. Worse when it's warm. Idle was maddeningly high and wouldn't adjust down, runs too rich then too lean, just all over the place, and sometimes runs great and other times stalls 20 times on a 10 mile drive. Backfiring has stopped with the carb work but still, the stalling!! 😫 Truck is otherwise awesome, 81k miles, was garaged until I bought it two years ago, and ran great until December 4th, when I had a tire blowout on the highway. It started stalling that day and hasn't stopped since. Starting to get paranoid about a curse. Engine was rebuilt 25,000 miles ago, have shop records from previous owner. Fuel lines were new about the same time, as they had some kind of stalling issue that turned out to be a fuel pump coming loose or something? Or the wires to it? I need to get that paperwork out again and reread the description of symptoms to make sure this isn't the same thing again but every mechanic has said it's not the fuel pump (nobody's checked it to my knowledge). This is driving me nuts and I just want my truck to run well again. Any direction on where to go from here is greatly appreciated.

13Swords

Sorry to hear about the problems. Yes, I have mostly solved the idle/stalling problems. it was a number of things, which I will mention below. You didn't mention if you are still running with all of the smog equipment hooked up or not, that can make a difference. Mine has been desmogged & only has 2 vacuum lines; one for brake booster, one for vacuum advance on distributor. I don't know the extent of the smog equipment on a '76, but it could be something to look at. My '78 had several electrically operated vacuum valves, none of which were working right, so out of the truck they went. On to more simple fixes that could help you...

1. You say it's worse when it's warm; I assume you mean when it's at full operating temp. First thing I'd check is your fuel pump resistor. This is usually a white in color power, cylinder shaped power resistor, mounted on a steel plate, which is mounted on top of your passenger side wheel well, in the engine compartment. It's job is to drop the voltage a little to the fuel pump, to keep it quiet and to lengthen it's lifespan. Your electric fuel pump in the tank does not need the full 12 volts to put out the correct fuel volume & pressure, so this resistor protects the fuel pump. When the resistor gets old (and I'm assuming you probably have the original in there), it can resist more voltage then desired. It dissipates electricity as heat. All those heat cycles eventually start to break down the wire winding in it, causing excess resistance. More resistance = less voltage to pump = less fuel, could = stalling problems. The nasty side of this is that it can vary with use, when it's worn out; sometime runs OK, sometimes 20 stalls in 10 miles, as you said.

The only way to test it is with a VOM meter (Voltage/Ohms Meter). If you don't have one you can get a cheap one from Harbor Freight for $6. Or your mechanic can test it for you. The base reading should be 1.4 Ohms, with a variation or no more then 0.1 Ohms. You or your mechanic can test to see if it's worn out by using the meter and a hair dryer. Hook up the meter, take a reading. Leaving the meter hooked up, turn the hair dryer on high and direct the hot air right at the resistor and keep it there for at least 2 minutes. watch the meter. if it starts climbing in resistance you've found a problem. On a worn out resistor, the resistance will go up when it is subjected to voltage, causing more heat, which raises the resistance, on & on & on. Mine read 4.8 Ohms after 2 minutes, more than 3 times the rating! Bad. Fuel pump was getting good voltage at start up (cold) but then got less & less as the resistor heated up. Maddening.

Bad news is that there are no new "plug in a new one & go" replacement parts on the market for this model truck ('75 to '78, '79 & up part won't work). Good news is that you can do one of two things. Unplug it & put a jumper wire in the harness socket, so your fuel pump gets full battery voltage, OR replace the resistor on the steel plate, which is what I did. It's a fairly simple job, two wires to solder & a little mounting work. You will need a power resistor rated between 1.4 Ohms to 2.0 Ohms maximum, 5 Watts power rating minimum. I got an aluminum cased one that stays cool at a local electronics surplus shop for $2 (used, but tested OK). it looks like this:

If you need more info on any of this let me know & I'll try to help you out.

2. What joints on what circuit boards are you referring to?

3. What exactly has your carb specialist done to your carb?

4. AAP. Auxiliary Acceleration Pump Diaphragm. This is located (usually) on the passenger side of the carb, a round looking metal plate with three screws.


If the diaphragm inside leaks, has holes or tears, and is still hooked up with a vacuum line to the VSTV (vacuum switching thermo valve) on your intake manifold, you will be running rich. Which is fine at start up, but not so good one warmed up. Can cause hesitation or stalling & fouling of #1 spark plug. Gas gets by the diaphragm, goes thru vac hose & straight into the intake. The vacuum valve could also be bad; I eliminated this valve when I desmogged, to make sure there were no extra vacuum leaks. I also capped off the AAP port on the carb. The AAP is there to reduce emissions on cold start-up & during warmup, but isn't needed when warmed up, or even to have the engine run OK at ANY temp. If your timing & ignition are OK, you're running pretty clean anyway. The carb is only 190 CFM, so there really isn't a bunch of gas getting dumped into the engine that isn't burning. I recommend capping off the port & vacuum valve.

5. Idle high, won't adjust down, rich then lean.
I assume by this you mean that adjusting the mixture screw don't seem to really control the lean/rich problem. Same thing for me. Plus, sometimes stalling at every push in of the clutch, sometimes not, sometimes idles rough, sometimes perfect, all without touching ANY carb adjustment screw at all! The solution was VERY odd to say the least. I doubt many mechanics would have even found it.

It's this: The throttle linkage. 1980 & older has a throttle rod between the carb and an arm on the firewall, that connects to the gas pedal arm. This rod has ball & socket joints. When these wear out, it can cause binding; either holding the throttle open past idle point (high idle non-adjustable w/idle screw), or allowing extra travel, allowing the throttle plates to close completely, causing a too rich situation @ idle. At idle, the throttle plates should be slightly open (there is a measurement for this in the rebuild kit instructions), never totally closed. The "slop" in the worn out ball & socket joints was causing my problems. There should be zero play in these joints. Mine had almost 1/8' play in each joint (2 joints on the rod, total 1/4" out!)

Again, new replacement part is not available. I fabricated a new rod with new joints, installed it, and almost all of the idle & stalling problems went away. It's still not perfect (needs tweaking) but it's very close. If you want more info on how I did this let me know & I'll provide details. Or you could ask your mechanic about the possibility or replacing it all with a later gas pedal setup with cable instead of linkage/rods. Toyota went to a throttle cable system in 1981 & never looked back.

Sorry to be taking so long, but I wanted to give you some ideas of what to have a look at; things that on mine definitely either fixed a problem or made an improvement. I've never had to deal with a vehicle this old before, & didn't know that you basically have to check every component in a system, due to wear, even the small things that almost no one ever replaces. These trucks are pretty basic, but that just means if 1 item isn't right, the truck won't work right.

Other stuff: Check, inspect or test - timing, ignition system including ignitor, electrical connection to ignition, fusible link wire (can be intermittent), valve adjustment (this last isn't likely to be causing your problem, but is worth verifying that it's correct).

So there's some stuff for you to dig into. let me know what happens or if I can help you out further. Good luck.

amit65

Hi..


Great truck, I had an 83 for awhile, till my father tried to go to town with it when I was in the middle of an oil change. (Bought the wrong filter, ran to town myself..)
My ’81 Celica has the 22r, still runs great. But after almost 30 years, many sitting on flat tires until its brought out of hooning retirement, the body is getting dangerous. Keep thinking about getting a good welder and tube-framing a chassis to drop the engine and 5-spd in. Like a big go-kart. Lots of logging roads/trails in Northern MN i could truck that combo up to.. Guaranteed I could destroy my own handy work before I could blow up the engine. B&B, what should I do with my fading yota?

PREVENTATIVE VEHICLE MAINTENANCE

Martin Burkhart

you have familiarised yourself so much with all of these systems on your '78, you could become a vintage Toyota Tech Specialist Advisor. I own a '79 that I recently purchased, and your thread has helped me immensely. It wouldn't stay running replaced relay tested and did maintenance on several noted system components now runs like new. Got to really looking, and realized that the 90k on the speedometer is accurate. What a steal for $500, thank you for all of the information.

13Swords

You're most welcome my friend, glad that all of my ceaseless drivel helped someone get their truck going again!

13Swords

UPDATE


I have FINALLY got the idle to a fairly consistent point, AND have got her idling at the prescribed 800 RPM hot. For a 40 year old motor it's way smoother than I have a right to expect; way happy. I have also cured an ongoing "hard hot start" problem that I've had since rebuilding the fuel system & installing a pro done (supposedly) freshly rebuilt carb. Here's all the gory details:

1. De-Smogging. Yes you can de-smog these trucks and keep the stock carb (can't afford $300+ for the Weber 32/36) and it can run very well indeed. But there are differences between the Weber & the stock carb. The Aisin fuel return line is NOT a fuel return line like the Weber; It's a VAPOR return line. It vents the fuel bowl of fuel vapors (as gas readily vaporizes off, even without the underhood heat). I had this line connected to my "fuel return line" which is steel & goes to the gas tank. WRONG. That steel line from the tank is there to vent the tank of vapor, in the stock setup. BOTH of those lines used to run to the EVAP Charcoal Canister to catch & trap fuel vapor, which is then sucked into the carb & burned off at a later time. This is all part of the emissions system, all of which I ripped out. Having the lines hooked together the way I did was only causing pressurized fuel vapors to be pushed into the top of the fuel bowl, up the vent tubes, then dump down the carb throat, everytime I shut the engine off. This loaded the intake & engine with fuel vapors so rich it would not start unless you cranked the hell out of it to clear it (20 to 30 seconds of crank with no sign of a "catch"). Bad all around.

So what I did was re-install the EVAP canister, re-connect it to the tank vent & fuel bowl vent lines, and connected the vacuum purge line to ported vacuum (Tee'ed into the distributor advance line). This way it would draw vapor only above idle speed & not mess with my idle mixture setting. This substantially improved the hot hard starting problem, but did not cure all of it. IF YOU'RE DE-SMOGGING & KEEPING THE STOCK CARB I RECOMMEND YOU KEEP THE EVAP CANISTER. You don't need or want the canister with the Weber, as it actually returns liquid fuel instead of vapor. Your stock gas cap should be up to the job of venting the tank if tank pressure gets too high, as it should have a relief valve built in. Also, make sure you cap off every unused port on the carb with quality vacuum caps to make sure you have no vac leaks.

2. PRO Rebuilt Carb? Yeah, maybe...
I got a "professionally" rebuilt stock carb, correct to my application & truck year, that was supposedly flow tested & even live engine tested. Yeah, not so much. The rebuild work was good quality, but apparently they did this one's testing late on a Friday, BECAUSE EVERY POSSIBLE ADJUSTMENT & SETTING WAS WRONG OUT OF THE BOX. Ugh. Yes I did re-adjust it I got it running, just no consistent idle & still the occasional popping backfire in the exhaust. Plus the hard hot starting issue. I didn't bug the carb builder about this, assuming it was something I did wrong on the de-smog. Plus I don't run the truck in such a way where the hard hot start issue got in my way (too much), so I lived with it. I recently got tired of dealing with it & wanted it fixed & finally found a solution.

Turns out the main cause of the bad idle & exhaust popping was the Throttle Positioner (otherwise known to the rest of the world as a "Dashpot") was adjusted all the way out, & making no contact at all with a tab on the front end of the main throttle rod. Apparently it came that way from the rebuilder

Why does it matter? Adjusted out like that, with no contact or influence on the throttle rod position, the throttle butterfly valves in the base of the carb were not in their proper position, actually being a bit "too closed". This was messing with the idle outlet port in the throat of the carb, blocking it slightly. This also allowed the butterfly plates to slam closed when letting off the throttle, causing an instant rich condition, idle bogging, sending rich fuel mixture thru the engine (which doesn't burn), pumped out into the exhaust pipe, where it found an oxygen source & POP, exhaust backfire.

The Throttle Positioner (Toyota's name for it) or Dashpot is supposed to "catch" & cushion the throttle return the last 5% of it's travel towards idle position, to prevent the throttle plates from slamming closed & causing the above described problems. With the adjusting screw backed all the way out, it does NOTHING.

How to fix? Easy, once you know what it does & is supposed to do. I turned the screw in until I fell resistance. Turned some more, watching the main throttle rod for movement. Started & ran up to operating temp. Pull throttle so engine is at 2000 RPM, then let go. It should settle back to idle in about 2 seconds. My initial adjustment yielded 3 seconds so I backed the screw out a bit until I got the 2 second drop consistently.

After this I was able to "snap" the throttle & never got another POP from the exhaust pipe. I was also able to set the idle for the stock 800 RPM, AND get the Idle Mixture Screw to actually do something (adjusting it before changed nothing, regardless of position.) Now the engine idle smooth at 800 (in fact smoother than I can ever remember, & I've had this truck 20 years!) It also now settles back to that idle almost every time I let off the gas pedal. It also completely cured the hard hot start problem (been testing for several days, now it starts hot within 1 second!) 9000% improvement!

Settles back to idle "almost every time"? Well yeah, there is still a small problem with the throttle linkage. As previously described, I fabbed up a new throttle link rod with two new ball/socket joints & that helped the problem quite a bit. Only problem is that there are 2 more ball/socket joints that are likely worn & causing an occasion bind in the throttle linkage. These 2 are on a small connecting rod, that connects the gas pedal arm to the rest of the linkage. it's located inside the cab & is not easy to get to. I also am not sure yet just how to get it apart in a view to fabbing up a new rod with new ball/socket joints. Anyone ever messed with these? Tip, tricks, well wished? All would be welcome. Otherwise I'll need to dive in, rip it all out & go from there. Of course there aren't any app specific parts available new. Now where did I put my engineer's hat?

Of course, I could just do away with the rod setup & convert to a cable (Toyota did this starting in '79 & has used it since), but $ is tight. I can afford some hardware & time to work on it better. The cable system requires more parts & even junkyard parts would cost me more than I have to spend. I'd even have to get a different pedal setup made for the cable. Bleah.

So that's the update. Sure wish I knew about that throttle positioner sooner. I will add to this if anything important comes up. Thanks to everyone who read, responded & tried to help. You guys are the best.

13Swords

Figures. I finally get the fuel problem under control & 2 days later the ignition coil decides it's about to die.
Apparently the last chain in the hard hot start problem chain. Cheapie Chi-nee coil only lasted me 2 years; upgrading to a Standard Motor Products UF2 coil. Always sumthin...

Remember kids, NEVER cheap out on your ignition parts!

hammersandwheels

so is throttle positioner your final diagnosis, Dr. Toy Ota?
imagine you were back any the beginning now and came across this information you have so generously shared with us. What would be your first move?

13Swords

Well no, the Throttle Positioner is NOT the final diagnosis, but one of the final items in the chain of failure. The final items were the coil going bad & it taking out yet another ignition module (both replaced with new, quality items) & a wear problem with the throttle linkage. The specifics -

Ignition Coil. This was a low quality coil that did not last (Spectra Premium # C624, cost $8). It didn't last very long, developed internal shorts in the coil & exhibited a nasty hot start problem. It had to sit & cool for 20 minutes before it would work again & let me start the truck. I replaced it with a Standard Motor Parts coil (Part # UC12, cost $22). The shorted coil got very high in resistance & killed my ignition module, so I also had to replace the GM HEI ignition module that I converted to as the bad coil fried my old module (Standard Motor Parts #LX301, cost $20). I converted to the HEI module because a new replacement Toyota-style "ignitor" was $400! Since putting the new parts in the engine runs very well & starts hot every time.

Throttle Positioner. This is also known as a "Dashpot" on carbs. It's job is to catch & cushion the throttle linkage at a timed rate when you completely remove your foot from the gas pedal, to prevent the carbs throttle plates from slamming closed, which causes a momentary over-rich condition. The momentary over-rich condition was adding to the tailpipe "pops" I was getting on deceleration. Apparently this little item was NOT properly adjusted by my carb rebuilder. It was a little "off" & adding to my difficulty in diagnosing & fixing the running problem. The carb was supposed to be live run tested by the rebuilder so I did not expect this adjustment to be "off" the way it was. A little fiddling with a screwdriver & some drive testing got that one sorted out.

Throttle Linkage Wear. Giver that this is a 40 year old truck there were bound to be wear problem, but this one takes the cake. Even after fixing all of the above I STILL had run/drive quality problems & the occasional tailpipe "popping". Turns out that there are certain places in the throttle linkage that had worn, causing some slop & sometimes binding, which affects the throttle position on a random basis (NOT good & NOT consistent!) I had previously replaced the ball socket joints on the throttle rod & that improved things some; the old joints were worn out & sloppy. Then I looked at the gas pedal linkage, which has a steel rod through holes in a steel plate bracket. The rod had a groove worn on 1 side where the plate had worn it away, to the point that the rod was a bit "floppy" in the bracket. I welded over the groove to add metal then reshaped the rod back to round (grinding, sanding). Re-assembled & lubed. That also helped the issue a bunch but still didn't solve it all. Last piece on this is a hinge assembly on the firewall that connects directly to the carb linkage. Turns out it's worn as well; the hinge barrels are loose due to wear on the hinge pin. More slop & binding. Argh.

I haven't torn into the hinge yet to try to repair it (I assume it's going to take a fix like the gas pedal linkage). I did blast it with brake cleaner & oiled it up good with a few drops of auto trans fluid & that helped, but it still acts up every other drive or so, still binding.

For the record & from research I have done, apparently 1978 was the last year that Toyota used a throttle rod linkage system on the trucks. They switched to the more familiar throttle cable system in '79. If I had known what a headache a worn out throttle rod system could be to repair, I think I would have just converted it to the cable system from a '79 & up & be done with it.

If I was back at the beginning what would be my first move? What have I learned? The first thing would be to realize that when you are trying to fix old vehicles, assume nothing. Get the factory service manual (FSM) so you KNOW what's supposed to be. I'd also assume that just because you find a bad part or assembly & fix it, don't expect to be done with the fix & don't expect it to work perfectly. Everything is connected & there is bound to be other problems within a certain system, ESPECIALLY on older vehicles. Not a lot of people (including me) think about the throttle linkage being a part of the fuel system, but it is. I've learned to look at whole systems; if it's connected to it, it's part of it. Don't expect an easy fix so you can drive it right away; almost nothing I worked on went that way. It was just time (or past due) to fix/redo/rework a lot of things on the truck. Small, often overlooked things tend to get more "prime" on older vehicles. Example: a 40 year old ground cable that was too high in resistance adding to ignition problems (who thinks of that normally?) Check/fix the WHOLE system.

This was also a "Do & Learn" experience for me, which is why it may seem like a lot of drawn-out & painful steps were involved. I also realized that a lot of these small, uncommon things are rarely addressed in any forum or FSM, so that's why I put out as much of the info that I learned here, so someone else can read through it & not go through the "hit or miss" process that I did.

hammersandwheels

thank you

Reelbilly

I started at 9:45 looking for posts on fuel relays and oil pressure switches to figure out what is causing my 78 Hilux to not get gas from fuel tank.
Here I am, two hours later, at the end of your story, having been totally absorbed and impressed by your persistence and learning experience.
Thank you for writing all this up, as I am sure it will help those who can find their way to your post. Was surprised to see there were few responses to
help you along, but you seemed to be covering all the bases pretty well.
Hope your truck lasts a million miles.

13Swords

Thank you for you most kind words. Helping others with similar problems was my main goal in writing all this up, & I am glad you recognized that, it's very gratifying. I am sorry it took you so much searching on YotaTech to find any answers, but with most forum boards like this that's pretty normal. Digging through supposition, guesswork and "bench mechanics" is often frustrating, I know. That's also why I wanted to post what was really going on with my truck & my efforts to fix it, right or wrong. There is no substitute for actual experience & data.

I hoped it helped you out. If I can be of any help to you at all just let me know by posting again. I will get email notifications. Thanks again.