[pist0lpete]

I run an HEI in my chevelle on a 350 small block. Whenever I got the car it ran decent but it didn't have an electric choke so i added one and it ran fine for a while. Then it seemed like sort of suddenly one day when we started messing with the timing it started to just go haywire. Me and my dad couldn't figure it out we went out driving just setting it by ear ie listening for the pinging and backing off from there. Well when we got it where it seemed it ought to be i get on it once and it revs up great barely a hint of detonation and good power. Then just driving along i start to go WOT again and it starts pinging all over the place. We try resetting the timing with similar results. Finally we pull off the vacuum line for the vacuum advance and after that we can get the timing set right. I take the car to a friend and we pull the distributor and discover the posts for the weights are looose so we frankenstein together a distributor with all good parts from the various ones he has laying around. Even after that its impossible to get it to run right with the vacuum advance. He even tested the vacuum bell or whatever you call it with his vacuum tester so i know its good. The only thing i think might bother it is the fact that i have the vacuum hook up for the electric choke tied into the vacuum line for the distributor. Would that be able to cause this sort of eratic behavior?

 

[DOUG G]

If the vacuum is erratic, then yes it will. I would also look at the advance weights to make sure they're not sticking or the spring is too light allowing the weights to open at will.

 

[pist0lpete]

It seems to me that it can't be the weights or anything because you can tune it in just fine as long as the vacuum advance is capped off. The problem before was that they were sticking since the posts were loose but now everything is in good working order. Im wondering if the choke somehow is sucking up all the vacuum maybe.

 

[DOUG G]

Unless there is a hole/leak in the diaphram, no.

 

[pist0lpete]

Unless there is a hole/leak in the diaphram, no.

Ya im positive the diaphram is ok because we checked it with a vacuum tester and it didn't leak down at all. I mean my car has a cam but not such a big one that i can't run a vacuum advance. Heck im running power brakes so that should be nothing.

 

[Schurkey]

So...What kind of electric choke uses vacuum? Or are you talking about the choke pull-off?

 

[pist0lpete]

Its a basic holley electric choke for a 750 double pumper. It just has a little like 1/8 inch vacuum line that i think its possibly used to cool the unit more than anything. The part that actually opens and closes the choke is the heat activated spring. Im not really sure what the puprose of the vacuum line is i just installed it per the instructions

 

[Schurkey]

That'd be for the choke pull-off piston. Most carbs use a diaphragm on the outside of the carb body, Holley often uses a piston inside the choke housing. Tougher to adjust, but once properly adjusted it works fine.

I wasn't thinking your car would have an external hose, the usual arrangement is to run an internal vacuum passage drilled through the side of the carb, and sealed with a tiny gasket--That's what they do on the electric choke version of the trusty 3310 750 vacuum secondary. I have seen some using that small external vacuum hose, such as the 850 vacuum secondary on the Crate 502 from Chevy.