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Jeep-Short Wheelbase All discussion of short wheelbase Jeeps: CJ, TJ, YJ

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  #11  
Old 11-04-2007, 01:19 PM
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OK, now that you have it running after all the troubles so far - time "dial it in."

HEI, MC2100 carb - you are close, but have the typical mid range stumble that combination creates. But once it's "dialed in" it's a sweet combination. You'll love it. I've done several conversions and
they always come out terrific.

First, make sure you have PORTED vacuum to the distributor. There should be very little vacuum at idle, and as you rev it up the vacuum increases slowly and evenly. Your fingers should be able to tell. Using the right vacuum is very important.

Since the stumble is at mid range (not just off idle like manifold vac would cause), I suspect you have the right vacuum now already.

So - next step - disconnect the vacuum, line and plug it, the see if the stumble goes away.
If it does stop stumbling, that proves the carb mixture is not at fault. And it proves the HEI distributor and the carb are not totally compatible. Easily solved.

The trouble is - the MC2100 has a very strong ported vacuum signal, and the HEI was originally used with carbs with a relatively weak vacuum signal. Mixing the 2 causes the advance to come in way too fast and too much - usually felt around cruise speed and feels like a lean carb.

The cure - an adjustable advance diaphragm for the HEI - then carefully adjusting it properly with TLC. Once that's done, you'll love the way it works. Cost is about $25 for the adjustable. But first don't just run out and get one - and for sure don't try to install it until we help you - else it'll really cause troubles.

Disconnect that vacuum line and try it - then let us know.
Obviously if it doesn't stop the stumble we need to look elsewhere for the stumble.

While you are at it make sure you do not have any vacuum line connected to the EGR valve, if so equipped.

Last edited by RRich; 11-04-2007 at 02:07 PM.
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  #12  
Old 11-04-2007, 03:41 PM
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ill give it a try and let yall know.......Thanks
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88 yj 9" lift 35" tsl/sx 258 strait 6

99.5 f250 ext cab 7.3 4wd AFE stage II intake 4" turbo back 5" miter cut stacks TS 6 pos chip wicked wheel boost regulator
33" tires
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  #13  
Old 11-05-2007, 08:32 PM
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Okay I made sure I had the proper vac. going to the distributor and I do.....I went to disconnect the vac line to see if it would make any difference and it didnt but I figured I would check to make sure it was connected to the distributor and guess what it wasnt...OOOOOPPPPPSSSSS, dont yell at me lol.....Anyway I hooked it up and hooked it back to the carb and presto it runs great at idle and I can rev it up where I want and hold it and no stumble but ( there is always a but with me) when I am driving, it wants to stumble as it changes gears and when I am going up a hill it doesnt want to downshift when I have it floored. I have been adjusting the kick down and it seems to get better the more and more I mess with it but I just want to make sure it is the kickdown not the carb mixture.........Like I said I made sure I have the right vac. to the distributor......So do I need the adjustable advance? Or just keep tinkering with the kickdown? Actually now that I read my notes over that from yall, I didnt try and drive it with the advance plugged. Should I do this?, the reason I skipped this step is because my dumb butt didnt have the vac hooked up from the start so I just figured that was the problem......I REALLY APPRECIATE YALLS HELP AND I AM VERY APPRECIATIVE THAT YALL HAVE THE PATIENCE WITH ME, I KNOW I AM A PAIN........
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88 yj 9" lift 35" tsl/sx 258 strait 6

99.5 f250 ext cab 7.3 4wd AFE stage II intake 4" turbo back 5" miter cut stacks TS 6 pos chip wicked wheel boost regulator
33" tires
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  #14  
Old 11-05-2007, 09:47 PM
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I'm a little lost now -
Did you set the initial advance to 8 with a timing light?

The kickdown is done with that lever - keep adjusting it slowly till you like it.
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  #15  
Old 11-05-2007, 09:51 PM
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yes I have it set at 8 degrees btdc
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88 yj 9" lift 35" tsl/sx 258 strait 6

99.5 f250 ext cab 7.3 4wd AFE stage II intake 4" turbo back 5" miter cut stacks TS 6 pos chip wicked wheel boost regulator
33" tires
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