yj rough running HELP!!!!!

[Rcwarrior]

I just bought an 89yj with the 4.2L carbed. I am haveing trouble getting it to run properly.

It starts and warms up just fine, but when you get to normal op temp the problems start.
it seems to have an intermitant miss after it gets warm and then when braking it will even sometimes stall.
As you slowly give it gas while in park (and when driving) you can hear it studering.

I am at a complete loss.

i did check the basics, tune up, carb and intake air leaks (now fixed) ignition system is all but replaced. reset the timing numerous times but no success.

If there is any info you can help me with i would appreciate it.

Thanks,

 

[88Wrangles]

How's your fuel filter look? Spark plugs?

After that...is the choke sticking on the carb?

 

[Rcwarrior]

filter and plugs are new, choke was sticking but is fine now

 

[redrooster]

Vacuum advance hose? (hose from carb to distributor)

 

[yjdave]

Start looking for vacuum leaks. The 4.2 in the early yj's is shiiiit. There is so much crap hooked to that motor (that shouldn't be there) i am amazed it even runs more than 6 months from the factory.

 

[TWDJ]

A couple of thoughts ...

1 - Can you get a comparison on fuel mileage before and after the issue began? A fuel float may be out of adjustment or heavy and you are actually running rich. While running, look for black smoke and check the tailpipe for that characteristic black, chalky fuel residue.

2 - The way I look for leaks, which is not always "best practice" is to use WD-40. Spray in short bursts (don't drench) around vacuum hoses where they enter the engine and other devices and listen for the engine speed to change. When spraying at a vacuum leak, engine speed will increase for a moment then drop back. Remember you have hoses at the axle disconnect and transfer case.

If you do not find a vacuum leak, it may be time to rebuild your carb ... or replace from what I've heard and read.

Hope this helps.

 

[88Wrangles]

If you can get ahold of a smoke machine...that will be the best way to find a vaccuum leak.

Just leave the engine off, inject the smoke into one of the vaccuum lines and let it fill up the engine and all the lines. Then just watch for smoke coming out of any of the lines. That's really the only way to track down all the vaccuum leaks...

 

[tint_rookie]

could the nutter bypass help in such a situation?

 

[jaymz77]

Have you done a compression test on each cylinder? If your compression test reads that the cylinders are not compressing get a bottle of "Seafoam" or B-12 chemtool from a parts store. When the engine is running pour about 1/3 of the fluid in the bottle in your carb slowly until the engine almost dies. If your engine is ready for an oil change pour the rest of the fluid in your oil and run you engine at around 2000 rpm with the vehicle sitting still for 20 minutes. Do not put the engine under any kind of load when doing this. THEN CHANGE YOUR OIL! I did this on my fuel injected 88 YJ 4cyl. and my compression tests rised about 10 psi on each cylinder. Good luck.

 

[Rcwarrior]

Thanks guys, i cant remember all the suggestions but here it goes,

vac leaks checked out and fixed. i am replacing a bunch of them anyway just because they are looking pretty bad.
seafoam done (i love this stuff, i have used it in all my old engines)

the distributer is pretty worn so i just ordered a new HEI from CRT performance. i will be doing that and the compression checks tomorrow.

then as TWDJ says, it may be time to bite the bullet and go the new carb route.

ill let you know what happens in a day ot two.

thanks again everyone,

 

[TwistedCU]

Your local emmissions testing laws will dictate if you can get away with a Nutter bypass. If you can do it, do it.

You should modify your carb to idle smoother via this procedure:
http://www.jeeptech.com/engine/carter.html

That should be done no matter what, the idle tubes were too small (engineering brain cramp). I'm not positive if this is your problem, but I'd be willing to wager that it will help.

keep us posted of your progress on it. I'll hopefully be doing it myself soon.

 

[Rcwarrior]

ok guys, time for some more help.

i got the new hei distributer in today and have spent the last 4 hours trying to get this darn thing running again.

i followed crt instructions to the "t" actually did it twice to make sure i didnt make a mistake the first time.

when i crank it over, she sounds real good but like there is no spark so i checked with the old screwdriver trick and it puts out a great looking spark.
thought maybe i was 180 out so i swaped the wires around and the same thing.

one thing i am wondering is about "disconnecting the old ignition box" after i did this i found that the yellow 10 guage wire is the one that had power on it when i went to the aux position with the key. this is the wire i tied into for my hei setup.

Has anyone else had this problem? what did i do wrong?????

thanks,

 

[Rcwarrior]

Just a quick update,

It is running much better, hei and weber 38 have really woke up this engine. i think i need a little more fine tuning on the carb. is there any tech pages on tuning the weber.

thanks,