'74 FJ40 won't idle. Need Colletive MUD brain!

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How about cupping your hand over the carb horn? Can you steady out the idle by covering the carb with your hand and metering the air (with zero choke) until it evens out and runs steady? If you then close your hand over the carb and cut off all airflow to the carb, does the idle rise sharply before the engine dies?
 
Cupping a hand over the carb will also improve idle. The engine is starving for idle fuel.
It's either a restricted idle circuit or an unmetered air leak (vacuum leak)..

It is possible that both carbs could have idle issues. The idle jet is the smallest fuel passage in the carb, so if there is any FOD, it appears in the idle jet first.

Do you have access to another engine? Put the carb on an engine that is a known good runner, see if it idles.

Disconnect every vacuum/brake/pcv hose from the manifold & cap off. Re-test idle.

Is the floor of the intake cracked?
 
Mine is a 77. I dealt with idle problems that about drove me crazy. Normal operation, if you look down into the carb while it is idling, you will not see gas coming out the venturi. The idle gas is coming in down lower where you can't see it. When mine was wrong, I would see gas coming out the venturi. That is because to get it to idle I had to screw the fast idle up so much it was forcing gas out the venturi. That is the only place it could go because the idle circuit was clogged. My whole issue was the idle circuit.
First time I fixed it, I totally disassembled the carb and methodically went through the idle circuit. For my carb, it leaves the fuel bowl, follows a passage up through the fuel cut solenoid, then down another passage to the idle mixture screw. My fix was when I removed the idle mixture screw and blew compressed air in the hole. A small piece of crud blew out of the carb passage and that fixed my problem.

Second time I fixed a no idle issue was when the fuse blew that supplies 12 volts to the fuel cut solenoid. That was a nice easy 10 minute repair. Mainly because I was sure the carb was clean and freshly rebuilt (and I had blown that crud out). I saw gas flowing out the venturi and immediately said "FUEL CUT SOLENOID!".
 
This morning, I checked and rechecked for Vacuum leaks using carb spray, propane and smoke, and just can not find any.

I think I may just have had the bad luck to get a second carb with FOD (had to google that, Jim :redface:). I will probably try and run the carb on the 60 to see if it will idle before doing anything else. And I may just replace the int/exh gasket cuz the one that's on there looks cheap (PO install w/headers) and I have a new Graflex Toyota gasket.

Checked again the FCS just cuz I'm paranoid and working fine, lots of loud clicking.

Thanks for all the help. :cheers:
 
Did you try an Okie Carb Rebuild? It could free up any FOD and temporarily clear your idle jet/circuit?

That might, at least, show you that it's the idle circuit and not a vacuum leak.
 
It sure sounds like some crud in the idle circuit. Also, did you remove the fuel cut solenoid? there could be some crud caught there clogging the passage through that. Don't assume anything. Some small thing could be causing you this big problem. I took the top section of my carb off, energized the full cut solenoid and then blew carb cleaner into the idle circuit passage that led through that solenoid and verified that stuff was getting through. That is what led me to the bottom section of the carb where the crud ended up being lodged somewhere down in the idle mixture screw area.
 
Hand over the air horn kills engine.

Can't really get any idle without the choke fully on - around 1000-1200 RPM.

Tried the :hillbilly: rebuild a couple of times with varying results I really don't understand: one time it seemed to run better for about 5 seconds, then died. Another time smoothed out then suddenly coughed and died. Kinda indicates FOD, yes ?

I think it's time to take carb apart and clean. I'm just kinda paranoid from my other experience with dissembling one of these :bang:

Shoes off and into the icy waters... :worms:
 
Spike Strip said:
choke fully on - around 1000-1200 RPM.

Tried the :hillbilly: rebuild a couple of times with varying results I really don't understand: one time it seemed to run better for about 5 seconds, then died. Another time smoothed out then suddenly coughed and died. Kinda indicates FOD, yes ?
Click to expand...

So, to clarify, you should cup your hand over the air horn loosely, with your fingers spread to reduce the amount of air going in, not cut it off completely. You should be able to get to a point where you can make it run without choke this way.

When you totally covered the air horn and killed the engine, did the RPMs increase momentarily before it died? If so, that indicates a probable vacuum leak. I know you are 99% sure there is no vacuum leak and are tired of being asked, but we just need to be SURE. Did you disconnect and plug the vac advance hose while doing this?

Stepping back and not necessarily related to the idle issue, are you confident you installed the jets correctly? If you cannot turn the fast idle screw far enough to get the truck to run smoothly around 1000 RPM (and no longer relying on the idle circuit) without choke, then you are running extremely lean and there is more going on than just the idle circuit.

Did you replace every part and every o-ring during the carb rebuild? I forgot one of the o-rings for one of the slo jets (I think that was it) during one of my recent rebuilds and it ran like poop. Also, make sure you reinstalled the venturi o-rings as well.
 
This carb was not rebuilt, or has ever been taken apart, FAIK. It is NOS unmolested Aisan. However, anything is possible.

RPMs did not increase with hand over air horn.

I did not plug the vac advance hose, but will check that now.
 
With idle adj screw turned all the way in, idles with choke off, around 1100 rpm - But fuel is dumping into primary ...

 
Fixed.
 
Ok, getting somewhere now. That is a lot of fuel. I thought you were running the rebuilt carb not the NOS one, not that it really matters. Did you correct what @FJ40Jim pointed out with the throttle return spring? How is your throttle linkage, is it fairly neutral when hooked up to the pedal? Did you check the idle mixture screw tip to make sure the the tip is in good condition and isn't deformed or mushroomed?
 
Spike Strip said:
With idle adj screw turned all the way in, idles with choke off, around 1100 rpm - But fuel is dumping into primary ...
Click to expand...

This is very normal behavior for a carb that has a plugged idle circuit or an engine with a vacuum leak. It is hard to believe that a new carb would have a plugged idle system, but it is possible. Why not try removing the idle mixture screw and idle cut off solenoid and aternately spraying inside with carb cleaner and comprssed air to see if you can blow the junk out.

If this doesn't work, you next move is removing the carb and doing a thorough cleaning or removing the manifold and resealing it.
 
Removed the carb for examination and cleaning and will probably reseal the manifolds while I'm at it, just to rule leaks out. Don't know what else to do, as said earlier, gasket looks cheap, but can not find any vac leaks, even using propane with a long tube to get under the bottom of the header flange...

Thanks again for the help, folks.
 
Good news Spike! The carb was test run (as shipped) on the dyno engine and it would not idle. Therefore, your engine is probably fine, and the carb definitely needs rebuilt.

Bad news is it will be a couple weeks yet to get rebuilt.
 
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