79 258 idle issues

[79cj7jeep]

this seems to be a common issue with the AMC 258 i6 / 4.2l . which i did have with my 80' also. but was alot easier fix.. but it just misses and sputters at idle... but i have isolated all my vacuum. such as modulator, QuadraTrac , vacuum advance, pcv.. and nothing changes.. put the timing light on to check and make sure it wasnt my timing chain.. my hash did not deviate at all.. also new cap rotor and wires.. from what i gather the last place to check is intake leakage.. motorcraft ignition module. and mybe replace the pic up.. i even went as fart to think it may be the modulator valve for the sheer fact i have gotten to idle smoothly.. but drive it and it start acting up again.. sometimes it worse than others.. oh ive rebuilt the carb and all the adustements have been put to spec, ie, float, vacum piston, accelerator pump, also made sure the idle tube were cleaned especially... sprayed carb cleaner all over the dang place also... and nothing at all.. this motor is fairly new as far as i can tell. the previous owners went through this from what i know.. but guess thats why i got it.. cuz they just threw there hands up, and said the forget it..lol.. any other ideas would be appreciated.

 

[NorthwestCJer]

What carb are you running?
Have you checked to see that the choke is not hanging up or setting itself?
Have you checked your compression?

Just covering it all to narrow it down.

 

[79cj7jeep]

i have not done a compression test..fairly new engine and this maybe the last thing i try.. for i dont have a guage.. but its a the carter bbd carb.. 8125 i believe. and the idle and sputter is through out cold to normal running temperature.. whether the choke plate is full open at running temp or closed at cold..i played with the choke some and its seems to be set right on.. the miss and sputter has been consistant lately.. but thats not always been the case.. it has been worse... and it has been better..

 

[NorthwestCJer]

I would check that the distributer isn't a notch out. It sounds like it could be firing out enough to make the engine shake.
Have you advanced or retarded the timing to see if it changes?
Without the vac advance hooked up on the dist, does it still do it?

 

[NorthwestCJer]

Have you advanced or retarded the timing to see if it changes?
Have you pulled the dist? may be a notch out of time.
Without the dist vac hooked up. does it still do it?

 

[Fastatv]

Hmmm, could be many things. When it misses and sputters, do you have an excessive fuel spell? Can you remove the filter and look down into the mini venturi and see fuel dripping? Is the venturi really black? Does the carb require a thick or metal plate under it to prevent perculation of the fuel? Just a few ideas for you. Fastatv

 

[79cj7jeep]

timing is spot on.. carb has been recently rebuilt and adjusted to factory specs.. i really feel its vacuum related.. or ignition module.. been to busy this week end to check anything else.. ill narrow it down eventually.. its just frustrating..

 

[79cj7jeep]

it seems the intake is seeled good.. and carb space and base seem to be seeled good too.. fuel filter replaced (again) checked fuel pump, got 4ounces of fuel in a few turns of the motor.. goin with the coil pick up or ignition module.. after that ill have to check for a low compression cylinder.. if not.. guess ill be looking for a chevy 350 w/ a good GM Turbo 400 .. i really dont need much of an excuse to go this route anyways..lol...

 

[alpha6]

Hate to bring this up...but you could have water in your fuel. It will cause it to sputter and act like you are describing, especially since it seems that you have done everything right. Pump some fuel AT THE CARB into a clear glass. Let it sit. Water settles; gas floats. If you see droplets in the bottom different from the gas then you got some water.

Good luck.

 

[79cj7jeep]

i didnt even think about water in the fuel. . i forgot to mention that i had about 13-14 pounds of vacuum.. is this sufficient.. with out looking it up.. i have no idea..

 

[79cj7jeep]

and i know i said pounds on the vacuum reading.. but it was a guage i had laying around my shop from some hvac stuff.. it wasnt in inches like it should be..