Ok, i was looking for some ways to improve economy and response in my 66 beater so were not talking thirdgen, but its still a gm hei.

I noticed the vacuum advance can was not connected, so i ran a manifold vacuum source to it figuring it would raise the idle rpm, as it did when i did the same thing in my 72. So here I am ready to calm down the idle and take it for a spin. I try to fire it up, and it wont go even though its warm. I give it a hit of gas and it fires, runs EXTREMELY lumpy (with a little foot feed i might add), and tries to die.

When i give it more throttle and the vacuum signal weakens, it runs better, then as i let off the gasm it sputters, bucks, and even gave me a backfire.

I know very little about distributor tuning, i do ecu tuning, so i have little knowledge.

Here are the symptoms of the problem I am trying to fix. At low speeds, the thing seems like it takes an awful lot of gas to get it moving. It constantly feels like its dragging an anchor. EVERY other muscle car ive driven has had more low speed response than mine, hell even my chicks volvo has better low end throttle response.

Am i barking up the wrong tree thinking that with no vacuum advance my problem may be timing related?

I mean running solely on initial and mechanical advance is for racecars, not daily drivers, right?

Thanks for the help guys,

I wouldnt be coming to you here for non thirgen related issues if i didnt think you guys were the most trustworthy source of info on the net. I cant wait to see what you guys have to say.

 

Assuming the ignition timing is set correctly check the little thin wires that connect the megnetic pick up coil reluctor to the HEI module.
When the vacuum advance moves the pickup coil to advance the timing in the distributor if the little wires are broken, the motor will missfire. This is a common problem with the HEI pick up coil.
Also if the rotor to cap terminal alignment is too far off center when the plug fires, vaccuum advance will make it worse. Rotor/cap phasing must be with in limits for adding vacuum advance will cause cross fireing and missfire.
How do you check and adjust rotor to cap phasing alignment? You get a old HEI cap and cut a hole in it below the #1 spark plug terminal on the side of the cap so that you can see the rotor spin around inside the cap. Mark the rotor on its side aligned with the rotor tip with white paint. Start the motor up and using a timing light connected to #1 cylinder aimed at the "window ya made in the distributor cap watch your paint mark on the rotor. With no vacuum advance it should be fairly steady as you rev the motor. Add vacuum advance and rev the motor and the paint mark on the rotor will move in the window. If the rotor alignment moves too far off the center of the terminal with rpm and advance, the motor will misfire. You adjust the rotor to cap alignment by either moving the cap on the distributor body or move the mounting position of the pickup coil on its plate in the distributor, or adjust the pick up coil mounting plate's position at rest in the distrbiutor body. "breaker point plate")
Usually its the little thin wires that connects the pick up coil to the module that cause the problem. Replace the pick up coil being sure to align it properly on the mounting plate. I believe the points on the pick up coil and star wheel must not be closer than .015" to each other.

 

would the broken wires explain why once the vacuum advance started tapering off the motot would run fine? It didnt misfire when i revved it a little bit, just down super low.

 

Yes This is a common fault with the HEI distributor.

 

It could explain that. The vacuum advance rotates the OUTSIDE (mag pickup) to advance the timing. The centrifugal rotates the INSIDE (spike wheel) to advance the timing. Lots of weird stuff can happen and flaky wires to the pickup can be one of them.

The other problem with stock HEIs is that the vacuum advance canister kicks in way WAY too much vacuum advance for a performance motor. Most of them kick in as much as an extra 20-26* of vacuum advance! A motor that's got the initial timing and centrifugal advance dialed in for maximum WOT scoot needs literally HALF that much vacuum advance (10-12*).

There's an article on this board's tech articles section about dialing in the HEI for maximum performance by yours truly. A good place to start. But it WON'T address issues related to actual failures/problems of the basic functioning of the HEI.

Replacement HEI distributors can be had for not much money (under $100), if you suspect yours is just too beat to fix. For example:

http://store.summitracing.com/partde...5&autoview=sku