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Discussion Starter · #1 ·
I have a 1983 CJ7 with a inline6 4.2L Need lots of work. Idled fine and run okay when I bought it this summer. Know it will not idle. I think it started after I replaced the timing chain (not sure). Have been massing with it for a long time.I can set the timing with no problem. Check top dead center right on. Has new plugs, wires, cap and rotor. I have a different carburator on it and it still will not idle. Know that it is cold. When the choke is on it idles on fast idle. When it goes off it will not idle. The fuel pump has 6psi at idle.I installed a clear line and has no air. I even ran it out of a gas can still will not idle.I drive it everyday to work and it runs good going down the road. But when I shift gears the rpm's hange up alittle. I have replaced the head gasket for a different problem. Plus I have sprayed ether around the carburator the intake and there are no leaks. When I get it to idle. It has about 18 ins of vaccum. But the gauge says that the timing is off. I'm all out of ideas.
Thanks Quack

· Registered
10,738 Posts
Great article.

Sometimes - not always, you can do it with a Mexican Tune-Up.

Rev to 2500 or so - put your hand - or a CLEAN rag - over the carb top, completely choking off the air. Let it die.
It'll be hard to restart, it's now flooded.

Now do it again.

What it does is you create a high vacuum in the carb, sucking all the junk out of the small tubes. Kinda like blowing your nose in reverse (yuk!)

Doesn't always work, but it's worth the try.
Good trail fix too.

Discussion Starter · #4 ·
also another way to do that is to use some pliers and clamp off the fuel line at the befor the pump, and rev the crap out of it until it dies, remove the pliers and crank the motor until she starts up. repeat
are u sure you got the timing marks right on the chain? did u reset your ignition timing??
low vaccum can be one of the following 1. a carb not set up right, 2. a vaccum leak,3. valve timing
here is something else to do
crimp ALL vaccum lines coming out of the carb and now start it and see how it idles
if it still wont idle then u know its not a vaccum leak in any of the hoses and most likely a valve timing issue
or your carb is not set up right

set up carb
plug all vaccum lines
put your vaccum gauge on a manifold inlet
turn the mixture screw all the way in
now turn it out about 2 turns
start car
slowly turn the mixture screw out until u get the highest amount of vaccum at the lowest rpm
hope that helps
good luck


· Registered
13,180 Posts
1. Go back to basics.
2. Statically time the engine.
3. Then recheck the timing under load.
4. Make sure you're timing chain was installed correctly,
5. By viewing the valves of #1 cylinder in the oil fill hole,
6. In the valve cover at TDC of the compression stroke.
7. They should both be closed.
8. If you've obtained a vacuum measurement,
9. Then you've got a gauge...
10. Is there ANY needle movement at a high idle,
11. Or is it steady.
12. If RPM's are decreased, what happnes to the needle movement?

· Registered
10,738 Posts
"also another way to do that is to use some pliers and clamp off the fuel line at the befor the pump, and rev the crap out of it until it dies, remove the pliers and crank the motor until she starts up. repeat"

Not to argue, but that could make even more problems. All that does is run the bowl out of fuel. At the bottom is where water and dirt hide. Just as it runs out it can suck it up. Then when you let new fuel in, the inrush can stir up the junk and get it in the idle or mixture passages.
And - when the bowl empties, the float might drag and catch on the bottom of the bowl, sticking. Then when it fills it runs over. That's a big risk if the last guy didn't set the float drop correctly.

The Mexican Tune-up sucks all the water and crud from the idle passages, jets, wells, emulsion tubes, dump tubes etc because of the high vacuum - hopefully cleaning them out - if that's what was wrong. It doesn't really disturb the crud on the bottom of the bowl - hopefully.

Either method has it's risks, just like blowing your nose, it can shove stuff the wrong way into your sinus - or worse.
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