Big Red is running rough
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Joined: Jun 2010
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Big Red is running rough
What does it mean when you plug the vacuum hose going into the vacuum advance module on the distributor with a golf tee and it runs fine...BUT...when you hook it back up it runs fine at idle but really rough when you excelerate?
Timing and points are set perfect.
I'm lost on this one.
NormF250
Timing and points are set perfect.
I'm lost on this one.
NormF250
Fleet Mechanic
Joined: May 2001
Posts: 1,396
Likes: 4
From: Cupertino
Norm, it sounds like the distributor is bad. The vacuum pulls on a diaphram which pulls the plate against springs to alter the timing. Something is going wrong in the geometry in your distributor. Possibly the little plastic bearings are shot.
I would get a rebuilt distributor and a new diaphram.
Semper Fi
I would get a rebuilt distributor and a new diaphram.
Semper Fi
Senior User
Joined: Sep 2009
Posts: 198
Likes: 3
From: Burbank, CA
Yeah, that sounds like a blown diaphragm in the vacuum advance. As soon as you get above idle, and the carb port tries to apply vacuum to the advance unit, it just sucks in air through the hole in the diaphragm. It's not just a vacuum leak, which will make it run lean overall, but the incoming air will be coming in through that port right in the throttle bore, which is going to mess with the air flow around the throttle plate area, disrupting the carb's ability to atomize the fuel. And, I believe the vacuum advance port is only in one of the two primary barrels, so one barrel would be working okay, while the other would be burping and coughing.
You probably only need a new vacuum advance unit, not a whole distributor. But while you're working on it, it wouldn't hurt to check out the mechanical advance mechanism to make sure it's lubed and free moving. Check out the shaft bushings too. If it's all worn out, then a whole rebuilt distributor may be the simplest and cheapest repair.
You probably only need a new vacuum advance unit, not a whole distributor. But while you're working on it, it wouldn't hurt to check out the mechanical advance mechanism to make sure it's lubed and free moving. Check out the shaft bushings too. If it's all worn out, then a whole rebuilt distributor may be the simplest and cheapest repair.
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