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Discussion Starter #1
OK, just to make sure:

Where do you hook up your vacuum advance from distributor to on a holley carb?
 

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Discussion Starter #2
WOW...nobody knows this?
 

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To the port in the front at the bottom near the base plate.
 

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Holy Sheit!!! Man am I a dumbazz!!!!!!! I hooked it up to the oneon the side above the idle mix screw.......


Would that explain why I am getting a big dead spot then backfire through the carb?!?
 

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67mike said:
Would that explain why I am getting a big dead spot then backfire through the carb?!?
That sounds more like a lean spot. Does this happen off idle? You might have to put some bigger shooters in it. Go up .003" at a time. If you are very careful, you can drill them with a precision drill bit set.

Exactly which carb do you have? What jetting? What about the rest of your combo (trans/gearing/cam/heads)? Maybe I can help get you in the ball park.
 

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Discussion Starter #7
StangLX302 said:
That sounds more like a lean spot. Does this happen off idle? You might have to put some bigger shooters in it. Go up .003" at a time. If you are very careful, you can drill them with a precision drill bit set.

Exactly which carb do you have? What jetting? What about the rest of your combo (trans/gearing/cam/heads)? Maybe I can help get you in the ball park.
Long story:

My car is at the body shop getting restoration completed......installed my Brand New Quick Fuel Technology Pro Vac 750 on to my 351W (replaced my 750 edelbrock). Anyway, it fires up, but it has a hesitation and then backfires through carb when you give it gas off idle and even when it is at about 1700rpm and you give it gas.

I called their tech and said wtf??? He said it sounds like accelerator pump circuit....so I will check that the accel plunger has no slack, that it is centered, and that the fuel shoots out of both squirters.......if not, I will remove squirter and free up the check valve in there. Sound about right????

BUT, I did hook my vac advance to the sprout above the idle mix screw, therefore I am getting full advance too early.

It seems to be a lean problem, and I will check those areas first.

Thanks
:cool:
 

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To be honest with you, I wouldn't run a vacuum advance at all. The centrifugal advance in the distrib will be plenty. When you hooked the line to that upper port, that actually causes it to come in later, it's a timed vacuum port. The lower one is a full vacuum port. I would set it up so that you have about 14-16 degrees of timing at an idle and in the mid 30's at 3000 rpm and above.

Here is a great article on how to do that. They also talk about ditching the vacuum advance as well:

http://216.127.80.97/archives/2000/03/timing/index.shtml

By the sounds of it, I still think you need a bigger squirter.
 

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Discussion Starter #9
StangLX302 said:
To be honest with you, I wouldn't run a vacuum advance at all. The centrifugal advance in the distrib will be plenty. When you hooked the line to that upper port, that actually causes it to come in later, it's a timed vacuum port. The lower one is a full vacuum port. I would set it up so that you have about 14-16 degrees of timing at an idle and in the mid 30's at 3000 rpm and above.

Here is a great article on how to do that. They also talk about ditching the vacuum advance as well:

http://216.127.80.97/archives/2000/03/timing/index.shtml

By the sounds of it, I still think you need a bigger squirter.
Thanks!

It has 31 squirter.
 

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I'd try a .035". If that doesn't do it, drill it out to .038".
 

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67mike said:
Holy Sheit!!! Man am I a dumbazz!!!!!!! I hooked it up to the oneon the side above the idle mix screw.......


Would that explain why I am getting a big dead spot then backfire through the carb?!?

The ported or timing vacuum port is the correct port for your vacuum advance. You had it hooked to the correct port.

You don't want full vacuum at an idle to the vacuum advance. If the RPM drops any then the vacuum drops, causing the idle to drop even more, causing the idle to drop. You see where I'm going here.

Vacuum advance is there to improve light load/light throttle opening fuel mileage. That's why you use ported vacuum, it's highest under the those conditions.
 

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If the distributor is fitted with a vacuum advance unit, connect it directly to manifold vacuum.

I cut and pasted this from Edelbrocks web site. Holley's web site didn't say anything about it. Anyways, I would just eliminate it all together. Off the top of my head, I can think of 10 guy's with carbed 'Stangs I know (including myself) that do not run one. All of our cars run perfectly.
 

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That may be what the Edelbrock site says but all the car makers, Ford, GM and Chrylser use ported vacuum on their old carbed cars. I'd be more inclined to used them as an example than Edelbrocks website.

I just picked up an 1985 Mustang GT, the last of the carbed cars and a Holley to boot and once you trace the maze of vacuum hoses, the advance is hooked to ported vacuum.

I agree, you really don't need a vacuum advance. It's strictly a fuel mileage increase and only a slight one at that.
 

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Discussion Starter #14
Thanks guys.

Once I get her outta the paint shop, I am going to tinker!
 
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