Jacob Burges

Hello everyone, this is my first post! I am at a complete loss.

I have an '87 pickup with the 22r and standard Aisan carb with electronic choke, mass of vacuum lines etc etc. Truck used to idle perfectly smooth, but recently has developed what sounds like a misfire or spluttering at idle. Clearing it all out with a stab of the throttle pumps a bunch of black smoke out too. The carb sounds like its making a gargling/sucking sound at idle, and when its off and I hold the throttle linkage wide open gas just pours down into the intake manifold.

I've set the air/fuel screw and idle screw to factory recomendation, gone through the vacuum lines, im confident that they all go to the right places and have good seals and vacuum. I made sure the ignition is set to 0 deg, cleaned the points, and replaced with brand new spark plugs, gapped properly. I replaced the fuel pump too.

Possibly unrelated since its had this issue for a long time: when I'm driving at freeway speeds the truck will buck as soon as it begins to coast and I let off the gas, e.g. going down a hill.

Any ideas? Let me know if theres anything I should do to collect more information to help diagnose the issue.

Jacob

13Swords

Just my guess but partially or totally clogged idle circuit. The idle jet and internal idle passages are very small, so it doesn't take a lot of junk in the fuel to clog them up. The main jet is bigger so it's harder to clog up. When this happens, you are idling on the main circuit, which is feeding a too-rich mixture to the engine, and at idle it can't burn all the gas it's getting. That would account for the sputtering & misfiring at idle. Stabbing the throttle and getting a bunch of black smoke is an indicator of a rich condition.

When you said "... when I'm driving at freeway speeds the truck will buck as soon as it begins to coast and I let off the gas, e.g. going down a hill." that rang a bell for me. My 20R used to do that when it had a clogged idle circuit. I'd even get "backfires" at the tailpipe, when the hot metal of the exhaust would :light off" the extra unburned fuel vapors, when they got close enough to the end of the exhaust pipes to catch some extra oxygen from the air.

In my case, it was the modern ethanol/gas mix attacking the insides of my old fuel hoses, breaking loose small particles of rubber, and some of them got past the fuel filter & clogged up my idle passages. If your rubber fuel lines are 10 years old or more you should replace them anyway. Replaced all the rubber fuel lines with new, ethanol compliant hoses, new fuel filter, and cleaned out the idle circuit in the carb.

I made note of how many turns "out" from lightly seated the idle mixture screw was, then totally removed the screw. Removed the idle cutoff solenoid. Those two items give you access to the internal idle circuit in the carb. Also removed the bolt at the bottom passenger side of the fuel bowl. That gives you access to the Idle Jet. Used a can of carb cleaner with the "extension straw" that comes with it. To shoot cleaner into the idle mixture screw port, the idle cutoff solenoid port, and the idle jet. Let soak, then repeated several time, then applied a bit of compressed air to each port. Felt over the other "open" port for air flow while doing this. Once I felt a steady stream of air, I put everything back the way it was. Solved my problem.

It's easy & cheap & just takes a bit of time to do. It may or may not solve your problem but it worked for me.

Tims86Toy

There could be any number of things causing this. Your AAP could have a hole leaking fuel by, your needle seat could be stuck open flooding the bowl, trash in the idle circuit like 13Swords said. Pull your fuel-cut solenoid and verify it's functioning correctly. Just apply 12v to the PIN connector and see if it actuates. The FC solenoid is supposed to cut fuel (close) when you let off the gas on deceleration, much like you describe.

But it really sounds like you should just pull the carburetor and rebuild it. Running that rich can cause serious problems. Do you smell fuel in the oil?

Jacob Burges

Thanks guys, Ill check it out today as soon as it stops raining and let you know what happens. Seems very likely that junk got in the fuel as it was sitting for ~20 years before I got it (free!).

Jacob Burges

That was the issue! I sprayed carb cleaner in the spots you said and it runs like a champ now. Thanks for your help!