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I've got a 1988 22R pickup with just about everything emissions-related that goes to the carb disconnected, including the AAP, CB, CO, MC, FCS, OVCV etc. The only connections to the carb at all are the choke wire, fuel hose, throttle cable, and the two advancer vacuum lines. The EGR valve is still on the truck, but is disconnected.
The truck starts fine on high idle (I have it set for about 1500 RPM) but as soon as I blip the gas, the idle will drop down to like 400 or so and usually waver between 400 and 800, sometimes stalling out. I can crank up the warm idle to about 1000 and it will run fine there, sometimes wavering a bit, but anything lower than that and it wants to waver between maybe 600 and 900.
Normally I drive it with the idle set to 1100, and it performs fine there so I'm tempted to leave it, but I'd really like to get it back to normal.
Another weird thing, as the truck heats up (over 15 minutes or so) the "slow lopey idle" gradually begins to speed up and smooth out, but it never fully recovers.
Any ideas? The truck runs great everywhere except below 1000 RPM. My only guess is that the mixture needs adjusting or somehow the choke is not working right. (but it does get hot and open in a minute or two) I can manually hit the AP and the idle will pick up if that helps. I'm hesitant to adjust the mixture because I have heard horror stories about it but I'm thinking I have either a vacuum leak or the mix is off.
Here's a video. The engine was completely cold. I was wrong about the high idle speeds, but the results are the same. It's like it's coming off high idle instantly when I hit the gas, and the resulting "warm idle" is way too low. (At the end of the video I tap the gas which drops it off high idle and it stalls) What's not in the video is if I let it warm up for 10-15 minutes (thermostat opens etc.) the "warm idle" is fine.
Is there some way to slow the choke down or some other way to keep high idle for a longer period?
You can adjust the choke and fast idle by turning the black choke heater on the back of the carburetor. You might need to drill out the three rivets and put screws in it to make later adjustments easier. A properly adjusted choke will close when cold, then the fast idle will step down as the choke heater warms up. You might have to mess with the adjustment a few times to get it just right. There are marks on the top of the choke heater so you can get an idea of how far you are moving it when fine tuning it.
If the engine is actually cold (I am assuming your factory temperature gauge is not working correctly?) then the fast idle is kicking off way too fast. The choke either needs to be adjusted or something is wrong with the linkage. You are probably going to want to re-hook up the choke breaker and choke opener, also. The AAP is not necessarily a bad thing either, unless it has ruptured. I would not mess with the idle mixture quite yet.
I just had another thought. Did you disconnect the wires to the fuel cut solenoid? That would cause it to not idle properly. You will need to wire it so it gets power when the ignition is in the 'ON' position, and the other wire goes to ground.
Yes, sorry my temperature gauge is messed up. I do think the fast idle is coming off way too fast. When I got the truck (and before I removed all the vacuum lines) the fast idle worked great, that is to say it slowed down over the course of maybe 10 minutes instead of almost instantly. Also my current fast idle is really only engaging about half way. I think this is all indicative of the choke not being adjusted right anymore. Unfortunately mine has the rivets.
The choke opener only activates when hot, so I know it can't be causing my slow-cold-idle issue. The choke breaker from what I can tell opens the choke a little as soon as some vacuum builds. The idea is you need less choke once it's cranked I guess. I can hook that one up if I find a good source of vacuum. The huge vacuum fitting on the manifold has been removed, and I want to keep it off!
The AAP was leaking so I bypassed it. It does hesitate a bit when I stomp it, but that's only when cold (of course)
The fuel cut solenoid has been replaced with a bolt. I had planned on keeping it on there, but the "Deceleration fuel cut system" was causing it to kill my idle jet whenever the engine was above ~2300 RPM. That was a PITA to figure out.
For the fun of it I took what I think is the idle advance vacuum line off the distributor and connected it to the choke opener, of course it came off high idle and stalled. The CB had no effect. Just playing around, I held it up against the tube that goes diagonally over the secondary (circled) and the idle picked up. Does that mean anything? I'm still thinking there might be a vacuum leak or the mixture is off.
That tube is just a vent for the bowl. You were probably sucking up some gas fumes. Make sure the bolt you replaced the fuel cut solenoid with is sealed well, but does not block off the idle circuit. There is a choke breaker, which works exactly how you described it. It pulls off the choke slightly after it gets vacuum. There is also a choke opener that helps pull the choke open by vacuum after the engine warms up. It is easy enough to drill out the rivets and replace them with self tapping screws. It will be easier with the carburetor off the truck. You can also turn up the fast idle screw and see if that does anything.
You can also get a manual choke conversion kit if you wanted to try that. It basically just replaces the black heater with a cable.
Does idling up when sucking gas fumes indicate anything? I thought I read somewhere that meant the mix was off.
The bolt is a good bit shorter than the original FCS, and I think it's pretty snug, although I didn't put any sort of gasket on it.
I actually picked up a manual choke kit for the fun of it (It was $7) so I might try to take the automatic choke off mine anyway. I'm going for as much of a stripped-down, less-stuff-to-break setup as possible. This cold idle issue is my only stumbling block.
The mixture could be off, but it could also be a vacuum leak causing a lean mixture. If you have a small leak at the bolt, that would probably lean the mixture out quite a bit because it would take pressure off the idle circuit that goes to the venturi. I even wonder if the air gap created by a bolt would cause the mixture to change some. You want to get all of those problems fixed before adjusting the mixture. I would try putting the fuel cut solenoid back in, but wire it directly to switched power. Then check for vacuum leaks with a can of carb cleaner. A common source for a vacuum leak is the big nut that attaches to the EGR valve. If you disabled the EGR, you might just want to make a block off plate for the tube that connects to the manifold. Once all those things are checked, then adjust the mixture when the engine is warm and running well.
I still have the FCS so I can put it back in. There was nothing wrong with it, but I had the deceleration fuel cut system acting up (due to removing the vacuum switch.)
Another thing, the engine is actually missing at idle. When it's idling rough the muffler sucks on my hand and the engine wiggles back and forth. Could be FCS, could be vacuum leak.
If it's a vacuum leak, I need to find that sucker (pun intended) but I'm not sure what it could be. EGR block needs to be a priority.
Today I installed a manual choke (if for no other reason because I think it's cool and was $7) and sealed off all the unused vacuum ports. When I took the choke off I removed the CB and CO, as well as the secondary "lockout" linkage and metering needle flap (the thing that looks like a choke on the secondary, whatever that is). The entire secondary is fused shut so there's no point in having the linkages in the way.
Fed up with the normal vacuum caps, I soldered the fittings closed and sealed off the AAP with solder then JB weld. It was already disconnected, but the diaphragm was torn. Less stuff to break!
If it cranks tomorrow, I think I will have the most stripped-down stock carb in existence!
A couple things I spotted while looking at the still picture of the video, it appears like your missing a rubber vacuum plug (even though now your saying you've dealt with them). And it looks like your missing a screw to hold the top half of the carburetor to the middle half. It's right next to the block-off plate to OVCV.
Originally Posted by mct75
I removed the...secondary "lockout" linkage and metering needle flap (the thing that looks like a choke on the secondary, whatever that is). The entire secondary is fused shut so there's no point in having the linkages in the way.
The secondary valve serves a variable venturi for the secondary barrel. With it forced closed, I expect the power will be reduced. But let us know, I'm curious.
The secondary barrel has no venturi. Therefore the top plate initiates the vacuum to draw out fuel in the secondary circuit.
Plus in the video, I don't see the mechanical main accelerator pump move when you blip the throttle. Or it could be your not moving the throttle valve enough for the linkage to engage.
Thanks for the pointers! Good catch on the screw. Off the top of my head, I think I removed it when I took the wiring harness (choke heater, OVCV, FCS) off. I will look for it!
I've actually got all those vacuum ports soldered shut. I had horrible luck with parts store vacuum caps cracking and leaking on me. The solder should be permanent, but removable with some effort.
That diagram explains perfectly what the "metering needle flap" does. I guess when you're flowing that much air you don't really need a venturi. Except my secondary throttle plate is jammed shut. It looks like carbon/black goo has encrusted the shaft so thoroughly that vise grips just start to round it off. No idea what really happened but it will never open again. I'm happy with the lack of top end (a 350k mile motor should not redline anyway) so the one-barrel nature of it is fine with me. Opening the metering needle does seem to affect the idle (which is of course 100% primary) so there's an interaction there I am not understanding.
The accelerator pump does work, it just takes a bit more action before the cam starts to move. I have some pics and videos of me playing with it all.
Another thing, the idle seems to "creep up" as the truck gets up to temp (over a course of 15-20 minutes). What is a rough 650 RPM after 5 minutes will eventually become 1100 RPM after I drive for several minutes. It seems like if I correct this "fully hot idle" down to 700 RPM, the next time I crank it, it'll stall unless I leave it on high idle for 5 minutes. It's like something is changing as the truck gets hot. The automatic choke was kicking off in like 3 minutes, which was entirely too short. I've got the manual choke on there now, but haven't done a lot of testing.
Well, if anyone is still following along, installing the manual choke has helped a little. Being able to start it with the choke fully off has taught me that the choke isn't needed at all when the temperature is at least 60 out. I think some of my previous issues were from the choke being closed and not being opened at all by the choke opener.
That said, I still have the goofy issue where the idle creeps up based on temperature. The first 5-10 minutes it idles around 600 to 800, but after driving around some it will climb up to around 1100. I was really beating on it on the highway and when I stopped, idle was up to around 1400. If I correct this "fully-hot-idle" down to 700 or so, it wants to waver around, and stalls out when cold or slightly warm.
About 2 weeks ago I turned out the idle screw two turns, and the idle fell from 1100 right down to 700 and stayed locked in. When starting (with no choke), it would run at maybe 450 to 550 for a minute or two then come up to 700 and hold there perfectly. No missing or dieseling either. It was working perfectly. Key off and it stops right away, turn the key to crank and it fires off instantly and idles with no hunting or missing.
Last Friday, I came up to a stop sign and it stalled. I had to crank it for probably 20 seconds to get it to fire and it ran horribly. I had to hold down the gas to get it home. It's like it only wanted to run at 1500 RPM or nothing. Anything lower and it would cut out, miss and the idle will waver from 300 to 500 again, stalling most of the time. Futzing around with the choke, I went full choke while it was running (bad idea), and a bunch of gray smoke came out of the hood. I guess it backfired or something, but kept running the whole time.
I got it to finally idle again, by (you guessed it) turning the idle screw back in two turns. The idle jumps around, it misses, and diesels like mad when I turn the key off. It's back to the way it was.
Long story short, what the heck happened? It was totally perfect for like two weeks, then all of a sudden went right back to the exact same problem. Is there a jet or something that's clogged/stuck? Obviously the mix is off if it's missing, right? I can blip the AP and the idle will jump up, so I loosely guess that means the idle is too lean. I just don't understand what has changed in a way to make it go from crappy to perfect to crappy again when I haven't adjusted anything.
Not sure anyone is reading this any more, but I found a problem. My block-off of the AAP ports has come loose, and some gas was dripping from it. JB-Weld is supposedly "completely resistant to water, gasoline, and about every other petroleum product or automotive chemical" but maybe submerged in gas is going a bit far. The metal there is completely wetted with gas so I have been having a heck of a time getting anything to stick to it, and a new AAP diaphragm is way too expensive for a trashed carb.
I am hoping that the AAP outlet port was exposed, causing a vacuum leak, and fixing it will make it magically idle great again.
03-06-2016, 04:49 AM
