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Old 08-28-2012, 04:35 PM   #1
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how about you carb experts out there. I NEED HELP

I know im in the CJ forum but ive had no luck in the YJ forum on this issue so here it goes.

I have a 1990 yj 4.2 MC2100 carb engine and offenhauser intake manifold. Fully rebuilt by me and had a machine shop order all the parts and redo the block and it was bored out 0.030 over.

I have the HEI distributor and i have the jeep running and it idles well but it has a very loud backfire when you are coasting down the road after you have just let off from accelerating and im not talking about just some pops im talking about like a f..king gunshot. (Kinda scares the piss outta me when it does it) So any way i timed the jeep to 8degrees without vacum hooked up and with it at idle 800rpms and with the carb fuel/air mixture screws turned out two 360degree turns. from the sound of it idle and reving that seems to be a great setting.

Now my big question is when you adjust the carb and they say two turns out do they mean 2 FULL 360 degree turns or is a turn 180degree? (I hope you guys understand what im talking about)

And when i hooked up the vacum on the distributor the idle got a little jumpy and so i timed the jeep to 8degrees with vacum hooked up and it cleared out again but IS THAT RIGHT? I did not test drive the jeep with the vacum line unhooked so that could be my problem but i don't know. The only reason why i haven't test drove the jeep with it unhooked is because im trying to leave it hooked up cause the jeep ran great before with the old distributor(factory) with vacum hooked up and with the nutter bypass. but i will not use it if it seems to be the problem.

Some serious imput would be much appreciated! thanks alot jeepers!

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Old 08-29-2012, 02:21 AM   #2
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a "turn" is 360, but that's probably not relevant. If it sounds good and doesn't smoke up the joint, the adjustment is probably OK.

Issue is most likely with the HEI (you put a chevy distributor on an AMC engine, it's like dividing by zero...). I'd try different vacuum ports on the carb. The one your old points distro liked may not be the same one the HEI likes. Was the HEI new or junkyard? The vacuum solenoid on the distro might be hinky if it's a junk yard pull...

If it got "jumpy" at idle immediately when you hooked up the vacuum line, it's probably actuating right off the bat. The timing advance amount at idle with the line hooked up should be the same as the advance amount at idle without the line, it shouldn't be adding any amount of advance until it's throttled.

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Old 08-29-2012, 08:36 AM   #3
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Quote:
Originally Posted by aelwero View Post
If it got "jumpy" at idle immediately when you hooked up the vacuum line, it's probably actuating right off the bat. The timing advance amount at idle with the line hooked up should be the same as the advance amount at idle without the line, it shouldn't be adding any amount of advance until it's throttled.
im useing the same port as i did when i had my old distributor and it worked fine. I thought that is wasen't right when i hooked up the new one and the vacum line and it changed. I just wasen't sure if it was normal for an HEI distributor. I think i'll just not use it. And the HEI is new
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1990 YJ Wrangler 4.2 Inline 6 bored 0.30 over MC2100, HEI

2013 JK Wrangler Sport
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