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-   -   distributer vaccuum advance question (https://forums.off-road.com/jeep-short-wheelbase/188229-distributer-vaccuum-advance-question.html)

USMCYJ 03-03-2004 07:16 PM

distributer vaccuum advance question
 
I have my distributor advance line hooked up to the top port on my weber carb. I don't feel any suction when I cover that port with my finger but with a vaccuum gauge it tells me it pulls in some air. I can't remember the reading on the gauge. When it's hooked up to that port, the advance on the distributor moves. Should it do this or am I hooked up to the wrong port or what? I'm not too familiar with how the advance works so any and everything would help my limited knowledge on this. Also, when I take off the vaccuum line and plug it (and the port to the carb) it runs rough. I read a post on this and they said that it shouldn't move at idle. Correct? Incorrect? I don't know...
Tim

USMCYJ 03-03-2004 08:28 PM

Re: distributer vaccuum advance question
 
Well I'm gonna look into this a little more. I just checked out a few posts and found something that may help. I really am not good at searches. It seems so easy but I have a hard time with computers sometimes.
Tim

highfill 03-03-2004 09:58 PM

Re: distributer vaccuum advance question
 
You are running into the issue of ported vs manifold vacuum. Off the side of the carb is ported. Do some searches for "ported", "manifold", and "advance". Neither one is always right or wrong. Some engines use one, some another, some a combination of both.

You can also search on my username and will find a bunch of info on this topic. I used this forum extensively in researching how to tune both my distributor and my carburetor.

If I remember right, manifold vac is moderately high at idle, drops off immediately off-idle, then builds with RPM. Ported is closer to nothing at idle and builds with RPM. This would be why your engine changes behaviour... you are changing the amount of advance recieved due to vacuum.

1977CJ7 03-04-2004 08:33 AM

Re: distributer vaccuum advance question
 
I found this web page

Advance Curve Basics

Full of a lot of good information on advance curves and timing.

pnut 03-04-2004 10:15 AM

Re: distributer vaccuum advance question
 
I used to have a weber carburator on my CJ7 4.2L. I tried both ported and manifold vacuum.

I used manifold vacuum because it gave me better overall performance and proper advance when I needed it. I used the port just below the carburator baseplate on the drivers side.

I would suggest you try both, and see which gives you better idling, power, driveability, etc. Then leave it on whatever one is better.

USMCYJ 03-05-2004 06:37 PM

Re: distributer vaccuum advance question
 
I looked for ported vaccum on my weber and couldn't find one above the throttle plates. The one at the base of the carb draws in some vacuum; about enough to make the advance mechanism move about 3/4 of the way but once the gas is barely touched, it moves all the way. My idle is about 750, which is low for an automatic trans. But I'm sure there is a ported vacc. port on the weber, just where? I'm almost positive that it isn't the <nobr>engine</nobr> since it's 1 month old on a professional rebuild. So any thoughts, ideas, comments, constructive criticism? All are greatly accepted. thanks
Tim

WILL 03-07-2004 09:22 PM

Re: distributer vaccuum advance question
 
</font><blockquote><font class="small">In reply to:</font><hr />
I looked for ported vaccum on my weber and couldn't find one above the throttle plates.

[/ QUOTE ]

The port on the outside might not be above the throttle plates. The vacuum is drawn above the trottle plates on the inside though. Sounds like you might have found the one you need.


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