Engine won’t idle (1 Viewer)

[1978FJ40project]

My 1978 FJ40 will start up when choked, but won’t idle once I let off the gas. I removed the air filter and sprayed Carb Cleaner several times while laying on the gas ... didn’t help the issue. It has a new battery, new battery cables, new alternator , new starter , new ballast resistor .... my mechanic when I first got my rig said it needed a new Carburetor ... that was about 45 miles ago. Is it possible the Carb is just shot ? Right now I can’t even drive it to the mechanic to get the new Carb, so to get it to idle would save me a tow .... any thoughts ?

 

[Skeet]

A vacuum leak or fault in the ICS circuit are two likely places to start

 

[Honger]

Your idle solenoid on the carb is either dead... or the "engine" fuse is blown and your idle solenoid is getting no power... or the idle solenoid has become disconnected.

 

[JayDoc]

I don't know how far your mechanic is but more than once I've driven a truck with the choke open to keep it running.
Just a thought but I'd try what Honger said first.

 

[Honger]

I don't know how far your mechanic is but more than once I've driven a truck with the choke open to keep it running.
Just a thought but I'd try what Honger said first.

Great point @JayDoc, perfectly acceptable to drive it with choke open to your mechanic.

 

[1978FJ40project]

Your idle solenoid on the carb is either dead... or the "engine" fuse is blown and your idle solenoid is getting no power... or the idle solenoid has become disconnected.

Thanks - where would I locate the engine fuse to check it ? Forgive me I am new to this ... but will a new Carb have a new idle solenoid ?

 

[Honger]

Thanks - where would I locate the engine fuse to check it ? Forgive me I am new to this ... but will a new Carb have a new idle solenoid ?

A new OEM carb assembly does come with a new idle solenoid, yes.

Your fuse panel is below the dash in the driver's side footwell. It may or may not have a plastic cover over it. The plastic cover tells you which fuses represent each circuit.

 

[1978FJ40project]

Thanks, I have checked those fuses when I first got the rig... but I will check that fuse today when I get home. Glad to hear the new Carb will have the solenoid. My mechanic did a compression check and it was fine ... does that coincide with a vacuum leak ?

 

[Honger]

Thanks, I have checked those fuses when I first got the rig... but I will check that fuse today when I get home. Glad to hear the new Carb will have the solenoid. My mechanic did a compression check and it was fine ... does that coincide with a vacuum leak ?

Not really... vacuum leak can have multiple causes. Carb may not be true/flush with the intake manifold. A vacuum hose connecting to the manifold may be cracked somewhere. I'm doubting vacuum leak from your description of the problem though.

 

[JohnnyC]

Glass fuses sometimes have an end unsolder but the fuse looks good... fully remove the fuse inspect and put backnif good ... can even check power in and out with a test light if you want or voltohm meter

 

[Honger]

Also... while we are chatting carb/running issues... get yourself some pics and a build thread going man!

 

[1978FJ40project]

See attached fuse box in cab .... all the fuses are good. But I don’t see one labeled engine ... unless it’s the “meter” ...

 

[Honger]

Yeah, that isn't a stock fuse box...

 

[777Gage]

That's not an OEM Fuse Block from a 78, I'll post mine up in a couple minutes

 

[777Gage]

Here's my stock 78 Fuse Block

 

[1978FJ40project]

So would the fuse for the “engine” possibly be located somewhere else ?

 

[bentwigg]

I recently had a similar issue, was sure the idle solenoid was the problem - but it turned out to be debris in the carb bowl that was blocking the idle fuel circuit. I found the following post in this thread really helpful:

With it idling ( I guess you have to choke it, so hard to see I guess), is gas spewing out the venturi on the passenger side? Maybe you can back the choke out enough to see in the top of the carb. You should not see gas there when at idle. The gas should be getting to the intake via the idle circuit, which dumps the gas out below the butterfly at the bottom. If you see gas being dumped out the venturi during idle then the idle circuit is blocked some place.

In troubleshooting mine I traced the path of the idle circuit. Saw where the passages lead to the fuel cut solenoid. I energized the solenoid and then blew carb cleaner through the passage at one end and verified the cleaner spit out the hole that leads to the bottom section of the carb. This will verify that the fuel cut solenoid is opening.

I had an idle problem that sounds like yours and I ended up finding a piece of crud in the bottom section of the carb that was blocking the idle circuit. If you have the carb off, take off the top. Now remove the idle mix screw from the base and blow compressed air into that hole. This should force air out a hole in the bottom section of the carb that leads up to the top section of the carb, leading to the fuel cut solenoid passage. Make sure the idle circuit passage that leads up to the top of the carb is clear. That way you know that the gas coming from the fuel cut solenoid is getting all the way down.

And trace it through the bottom part of the carb where it leaves the bowl in the first place. It leaves the bowl through a passage, then goes through a jet and up into the top of the carb. Make sure that jet is clean. Once mine had the jet clogged and would not idle.

The gas being supplied for idle leaves the bowl through a passage, through a jet in the bottom part of the carb and then up to the top of the carb where it goes through the fuel cut solenoid. Then through another passage and down to the bottom of the carb on the passenger side where it gets metered by the idle mix screw and dumped out and goes to the intake.

 

[1978FJ40project]

Ok .... I’ll check that out.

any thoughts if my fuse bank has the engine fuse on it ?

 

[Steamer]

The idle solenoid is attached to the carb. You can locate it by observing the only wire that goes to the carb. When you turn the key to “on”, (not start) you can here it click if it is operating properly. You can have someone turn the key to "on" while you have your ear close to it listening for it. If you do not have a second person to turn the key, you can also disconnect the wire, turn the key to on and then connect the wire intermittently to listen for the click.

 

[1978FJ40project]

Here are some Carb. Picture to help