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Unread 10-18-2006, 11:32 PM   #1
jothorpe
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Join Date: Oct 2006
Location: Texas
Posts: 1
86 Laredo rekindled interest

Hi All,
Iíve just completed installing a new Weber carb and a HEI distributor on my 258 inline six. My question is what does the vacuum advance do? Do I need to have it hooked up to the distributor, or even the vacuum line that goes between my PCV valve and carb since the ignition control module is out of the equation due to the new carb and distributor?
Also my engine tends to sputter when I apply full throttle from a complete stop. This didnít happen when I had the stock distributor on with the new carb. Iíve played around with the timing between 7 & 10 degrees and it seems to perform the best at about 8 BTDC. Being curious I decided to look at the timing after I unplug and hook up the vacuum line back to the distributorÖto my surprise it jumps way up to 20 degrees before TDC, whatís happening?
BTW I would like to thank all of you who post and reply in this forum. Reading your comments has allowed me to ditch my mechanic and enjoy my CJ once again!
My Jeep was neglected for three years before I rekindled my love for the old CJ7 three months ago all because of the enthusiasm of you guys. Thanks again for the fun I'm having once again!!!

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Unread 10-19-2006, 07:19 AM   #2
gosupes
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1986 CJ7 
 
Join Date: Jun 2004
Location: Monroe, WA
Posts: 1,541
Quote:
Originally Posted by jothorpe
Hi All,
Iíve just completed installing a new Weber carb and a HEI distributor on my 258 inline six. My question is what does the vacuum advance do? Do I need to have it hooked up to the distributor, or even the vacuum line that goes between my PCV valve and carb since the ignition control module is out of the equation due to the new carb and distributor?
The PCV valve should be hooked up unless you want the excess pressure venting somewhere else like one of your pan seals. The vacuum advance line should be hooked up to a ported source, don't know if the Weber has one.

Quote:
Originally Posted by jothorpe
Also my engine tends to sputter when I apply full throttle from a complete stop. This didnít happen when I had the stock distributor on with the new carb. Iíve played around with the timing between 7 & 10 degrees and it seems to perform the best at about 8 BTDC. Being curious I decided to look at the timing after I unplug and hook up the vacuum line back to the distributorÖto my surprise it jumps way up to 20 degrees before TDC, whatís happening?
That's a manifold vacuum source you have it hooked to. Does it sputter with the vacuum hooked up or disconnected? Normally, you have the advance hooked into a ported source and you won't see any vacuum at idle. Once you hit the throttle, the vacuum kicks in and remains until you get near WOT when it will drop off. The manifold vacuum source starts off strongest at idle and will taper off as the throttle increases.
__________________
1986 CJ7, 4.2 w/4.0 head, TFI-HEI hybrid ignition, Clifford manifold w/Holley 390 w/cold air intake, OBA, 4.5" lift, Woody CV shaft and Tattons in front, 4.10 gears - lunchbox in front, Truetrac in the back, twin-sticked, blower upgrade for running topless, trying to keep it simple.

It's just a Jeep, and if you don't wheel it once in a while, it's not even that.
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