Aisin Carb issues (1 Viewer)

[petermac]

Aisan Carb issues

My 78 FJ40 (newly rebuilt 2F engine, Aisan Carb, Downey Header and Cam) won't hold an idle unless the choke is halfway closed. Problem started after I sent the carb (and engine) out for a rebuild (won't name the place where I sent it, yet). Initially, after the rebuild, the engine wouldn't hold a steady idle under aprox 1000rpm but it ran ok at speed. Problem got worse over the next two months, started having to close the choke a little until the engine warmed up. Now, as was mentioned, it won't idle at all unless the choke is partially closed. Two mechanics later, no vacum leaks detected, the diagnosis is blockage in the slow idle circuit. Does this make sense? Anyone encountered this problem. Might be looking to have the carb rebuilt by someone else or attempt the rebuild myself. I'm up in Canada so any ref's for a good carb rebuilder up here would be great, otherwise, I'll try to contact Jim C for a rebuild.

Peter Mac

 

[Pin_Head]

Two mechanics later, no vacum leaks detected, the diagnosis is blockage in the slow idle circuit. Does this make sense?

It is possible. It is more commonly a problem with the idle fuel solenoid cut off valve and its circuit. You would want to rule this out before you go spending a lot of money on the more complicated stuff.

 

[SpaceGhost]

Pinhead's on it, but another question:

Did you install a new fuel filter and clean out the gas tank? Years of crap in the tank will make short order of the freshly rebuilt goodies.

 

[petermac]

It is possible. It is more commonly a problem with the idle fuel solenoid cut off valve and its circuit. You would want to rule this out before you go spending a lot of money on the more complicated stuff.

Pin_Head: Thanks for the insight. How do you go about checking the idle fuel solenoid cut off valve and its circuit?

SpaceGhost: I did have a new fuel filter installed and the gas tank on my truck is only about three years old. I even changed fuel filters, again and cut open the old one to see if there was evidence any of crap in there, but it was clean.

Would be great if I could avoid dishing out for a costly rebuild, again!

 

[Pin_Head]

Generally, people check them by having someone turn the key on and listening with a stethoscope for a click (the VSV and other things also make a click). This indicates that the solenoid works but doesn't guarantee that valve is good.

If that doesn't clarify the problem, you can remove the solenoid valve and the idle mix screw, spray the holes liberally with carb cleaner and then blow them out with compressed air at about 90 PSI. You might get lucky.

What you describe is also typical for a major vacuum leak and I'm taking your word that you checked, but did you check the intake manifold at the exhaust manifold junction for a big nasty crack? This is pretty common too.

 

[jcj_78FJ40]

Yes, defiantly check your intake manifold. My 78 was having the same problem. I pulled the carb off to rebuild it and discovered a big crack in the throat of the intake. Since rebuilding the carb and having the manifold welded, my rig is running great!

Also check your PVC hose. A worn one can slide off easily and you will get similar symptoms.

 

[65swb45]

Ah, the infamous cracked 2F intake! One more reason I like my F engines!

You should DEFINITELY check for this.

As far as the idle goes, you should disconnect your choke and turn up your idle to see if it really is a choke-based diagnosis. The choke raises rpm AND vacuum by closing the aperature in the top of the carb, increasing demand. If you can get the carb to run with the choke open, then measure vacuum at the lowest rpm the engine will stay running at.

Also note whether you have gas coming out of the primary emulsifier. Chances are you do. If you cannot adjust a warmed engine to where it will idle without gas coming out of the emulsifier, then SOMETHING is wrong with your idle circuit.

HTH

 

[petescoffee]

may sound stupid and simple but, make sure the wires to the idle solenoid are hooked up. WHen I first started mine 2 years ago that was the problem with mine.

 

[Scalp]

I had that problem with my '78 FJ40. It turned out to be a small piece of stuff that was blocking the entrance to the slow idle tube in the carb. If you remove the top airhorn and lift it out, you will see a brass tube pointing down. The entrance hole is very small and can be cleaned out with a piece of small wire or one of those welding tip cleaners. To avoid this problem happening again, you must keep the fuel totally clean. I added a second fuel filter by Bosch that was made for Volkswagons and it worked great. So the Bosch filter was before the fuel pump, and the inline smaller filter was just before the carb.
The other thing is that the fuel level in the float bowl is very critical on those models. It has to be right on the dot on the float bowl window otherwise fuel will be dumped into the carb and run rich.

 

[hi50phd]

These guys must be pretty far from you (http://www.daytonaparts.com/), but they were the only folks who I could find that would consider rebuilding my '64 1/2 Mustang carb. Went to a TBI conversion, so I can't speak to the quality of their work.