BradAFR

It’s a novel...
My father gave me the pickup for free because he couldn’t get it running. It is a 1986 pickup with a 22r and stock carb in it. Over the course of a year he has replaced: fuel lines, fuel filter, fuel tank and sending unit, mechanical fuel pump, as well as modified it back to stock (it’s seen better days).
I started by taking the carb off and rebuilding it with a kit, as well as spare parts from the junkyard and modifying the automatic choke so it can be advanced and rotated. I fixed the linkage, new diaphragms, and adjusted (correctly I think).
Now... the truck will start cold and run just fine. It used to have a REALLY high idle, by ear around 2k rpm. Now it will run fine since I adjusted the carb until it gets hot and once I turn it off, it won’t start until it cools down. I’ve looked at the choke and fuel bowl level and although the choke is wide open, it still won’t start when hot. I’m curious if anyone has had this problem. It sounds as if it’s missing, like a bad plug or rotor? My next follow up is to do a general tune up and see where it leads. This is my first carbureted gas project, I’ve been to diesel school/gradiated and been mechanizing for almost 6 years now but I’m stumped... Any ideas?

snippits

When it goes no crank on hot again, give it a shot of starting fluid.

You said choke is open hot, but that still does not mean the engine is not being flooded. I had an old Oldsmobile that I had to pull the spark plugs, and then take my cigarette lighter to burn off the excess fuel. It would crank right up after that. Only did it when it was cranked hot. I had the choke wired open. Carb had to be rebuilt.

BradAFR

So most likely needs new plugs ya think? I’ve rebuilt the carb top to bottom already...That was my next move with a tune up, to do spark plugs and check wires and the rotor/distributor. It’s also got a vacuum timing advance on it for the emissions system, but I’m not sure how much that could factor into it.

BradAFR

I'm giving all of the info I can in hopes that it will help someone else somewhere... Today I did spark plugs,rotor, and cap on the truck. I started it and it was bogged down to LOW rpm's, and was having a hard time staying alive on its own. After it died, I looked at the fuel bowl sight glass and saw that it was completely full. I tore the top 1/3 of the carb off and adjusted the float again and after, it started right up. I adjusted the rpm's by ear to where I believed high idle should be and it ran absolutely fine. After it was hot, I shut it down and tried starting it again, with no luck...
I opened up the cap and began looking at the points under the rotor, but am familiar with them as I have always worked on and went to school for diesels. I will need to research this further. Talking with a buddy, he advised me earlier this week that as the engine heats up and expands everything around it, if the cap has a crack or hole in it that it will expand and make the rotor unable to contact the cap and you will get a no start when its hot. I've also noticed that when cold, the automatic choke (I have adjusted by taking a dremel and grinding off the tab on the metal housing to rotate it so the choke can keep light and constant pressure while cold on the butterfly valve) will begin heating up and opening it properly, and as it cools down it will return to normal. I know the choke operates itself from that 12v voltage to open it but will also use vacuum pressure to pull it back to closed. I've hit a bump and have to think deeper about what may be causing this. One observation, following the points wires from the distributor back to the "voltage regulator", there is a ground wire that is bare and corroded, but still in tact, from the control module underneath to the housing... I'm not sure what kind of problems that could cause. Has anyone had this problem? More to come as I work on the issues...

greyheadedguy

To run, that engine needs 3 things, spark, air and fuel, does yours get that once it gets hot? I struggled with a "die when hot" problem with my 87 which turned out to be a bad fuel pump. Had another fuel pump fail Saturday... When truck stops running, give it some fuel either a few drops of gas directly i the carburetor or hit it with some ether. If it starts you have a fuel problem... Then put a pressure gauge on your fuel pump and see if that's the problem... After market fuel pumps have only been lasting me 18 months, I will be replacing the one I put on Saturday with a factory part...

grey

BradAFR

Update:

Today I checked timing and adjusted it, which made a big difference in itself. It adjusts at 0 degrees at idle with the vacuum advance lines plugged off and 8 degrees advance with vacuum advanced hooked on. That's for the "gee whiz" file if it wasn't already known to some. When I adjusted the timing, it should be noted that the RPM's slowed WAY down, after which I went to the trusty screw driver and adjusted the carburetor back to where it sounded right. The timing light I borrowed did not have an RPM indicator on it like some did, or I would have adjusted to that approx. 950 RPM spec it calls for at cold idle.
Now... Having an assistant makes for a much more productive troubleshooting session, as I had my assistant hold the choke while I was trying to start it while it was hot. They first started by leaving it while I cranked and closed it until the truck fired and ran. It didn't start until it hit almost completely closed and then ran at about the same angle as the other barrel's butterfly valve sat. Anything after that angle, it would run like dog doodee...
So, I hooked up a long vacuum line, as an experiment and ran it so I could put vacuum on the choke rod and noticed this - The vacuum for the rod doesn't supply vacuum to hold it closed, it supplies vacuum to open it instead.
Having noticed that, I took the choke and made the adjustment for it to hold choke until it mimicked the other butterfly valve's angle. I know none of this is out of a technical manual, however, through trial and error, This information came like an epiphany to me and I finally understood exactly WHY it would not start with how I had everything set up. Hope this helps someone, more information to come as it becomes available.

BradAFR

Today, I decided since it was running pretty good I would do a valve cover gasket and change the coolant. I did both of those and put everything back together, new issue. It starts, but is really bogged down and I can smell gas. It also blows smoke out the pipe when it's trying to start. I did notice that if I put the accelerator to the floorboard that it will start and stay alive on its own, but not very well (very bogged down/low RPM's). I traced my footsteps back and made sure I didn't lose anything with my tools and rags, even taking the valve cover off again and....well... nothing. I'm stumped now. The fuel level in the bowl is completely normal and the choke is still operating fine. The only difference is that today it has been raining on and off and that I did the two maintenance actions to it. I will keep updating as I go on, but while I do.... Any thoughts?

superex87

With the these trucks at or beyond 30 years old the stock carb is worn out. You need to get yourself a factory service manual for that year truck and go through it. Each year the carb had changes made to it. The stock carb does not set up like common aftermarket carbs. Unless this needs to pass emissions I would ditch the stock carb and put a weber 32/36 on it and call it a day. I have been running the weber 32/36 for about 8 years now with little to no problems from it.

BradAFR

I thought about it, but this truck was free and I’m a nerd when it comes to diagnosing... Plus I want to do this and hopefully help someone out there who has the same problem someday. I’m wondering if the new aap diaphragm could be busted? Where it smells really rich but the fuel bowl level is good, it’s somewhere to start?

old87yota

If this Truck is not a daily driver, I would say just keep tinkering with it. The truck will be something that you can play around with, and not have to worry about getting it running to get to work in a few hours. I find diagnosing a problem is a lot more fun when you don't rely on that vehicle as your only mode of transportation.

Go ahead and check the Auxiliary Acceleration Pump diaphragm. When you take the vacuum line off of the AAP vacuum port, check to see of gasoline is in the line. If it is nice and dry, then the diaphragm is likely good and not leaking (but feel free to take the cover off and check anyway). If you see / smell gasoline in that vacuum line, the AAP Diaphragm is bad. There are three screws that hold the diaphragm cover on.

Do you have a Factory Repair Manual? It is pretty handy to help with diagnosis. Most of the "On-Vehicle" checks on the vacuum systems is in the Emissions Control section, rather than the Fuel section.
Yesterday I had a pretty severe misfire problem that just randomly came and cleared up, so I will be doing similar checks on my carburetor soon, just to see how everything is (or isn't) working.

Just as a side note:
These carburetors use Japanese Industrial Standard (JIS) type screws. The JIS screws look just like Phillips type screws but have a slightly different profile. If you have access to screwdrivers that are Japanese Industrial Standard (JIS) type, it will be easier to not strip out the screws. You can use a regular Phillips screwdriver (I did on mine), but you have to be more careful to not strip out the screws.

BradAFR

Today I took the carb off and decided to check everything twice.

There was fuel in the intake when I took it off, so it was flooding somewhere, even though the fuel bowl was within spec. I have a donor carb from the junk yard and put a better float set in and adjusted it, it looked in better shape than the one I had in this carb. I also did take the AAP covers off and check the diaphragms on the AAP, both of which were fine. I went further and adjusted everything while it was on the bench before putting it on (like I said "discount double check"). I did notice the spring wasn't set in its little hole or tight for the needle on the main jet either... After putting the new float in and adjusting it and getting the spring on the needle set, it was absolutely fine, I even drove it down the road and back no problems! The idle is a little high, but I can live with it for now. It starts both cold and hot with everything hooked up and going. I'm convinced that I may need to get the idle adjusted and take the poor old girl for a good drive to get everything loosened up and cleaned through the lines.

Unfortunately, I do not have a repair manual, but I do have friends that let me sit in the auto parts store yesterday and look over the manual for a couple of hours. I couldn't find a troubleshooting tree or anything, or even any new information that could help me further. Hopefully, this new gas through the system will clean it out. I've been wondering what additive I could add to the fuel that would help clean the system, any suggestions? I am between SeaFoam and some Star Tron. Between the donor carb and just tinkering with it, since it is just a freebie non-daily driver, I am confident that today could be the last time I need to tear the carb off for a while. It was, however raining when I drove it down the road and found: 1. The wipers do not work 2. none of the lights work 3. The front windshield leaks water. Hope this info helps someone, somewhere!

BradAFR

Today I have excellent news. The truck starts and continues to start, whether hot or cold. However, I would like to add some important information to this. When it is cold, the choke will work and start it in a spot and when it gets hot, the choke will do the same. My advice for any of this for anyone having the same problem: take a dremel tool and take off the metal tab that holds the choke in place. Had I have kept it where it was originally, the truck would never have started. I can prove this (to myself) by only having to rotate the choke, hot or cold, less than 1/4 of an inch total to get the choke to a sweet spot and it will fire right up! So...

My advice is to dremel that off, it gives you the opportunity to rotate it for that old choke bimetal spring to keep doing its job. I will post pictures of the progress of the truck. I'm excited and am glad to ask any questions someone has and I can answer.

Gee-whiz file: The junk carb and my original carb have differing carb #'s on the tag, but floats, jets, guides, etc. are the same inside. The only difference I can notice would be the gaskets used when tearing the old junker apart. The gaskets are slightly different, and researching, this is for different years of trucks with/without certain emissions and whether it is USA/Japanese/Canadian built vehicles.

Hope this helps someone!