:? Hey folks! I put in an HEI when I replaced the motor and I can't figure out why it won't run with the vac. advance hooked up. I've played with the weights and springs, put in an adj. advance unit ,but hooked up it don't run worth a crap. Finally set total timing at 34 degrees and called it quits. Runs good there but would like to get everything hooked up. Any advice out there would be great. And I don't know if its the distributer, it did the same thing with the old points one , thats why the HEI was put in.

Is this a recent rebuild?

It was a rebuild bought from a engine shop about 16 months ago. I've been driving it without the advance hooked up since day 1. Supposed to have an R.V cam with 202 heads. Put on roller rockers,Edelbrock intake and carb. Not being much of an "internal" motorhead It's just got me baffled. One of them things that just keeps knawing away at a person. Checked the obvious things, timing marks lining up,etc.,etc. Has had me stumped along time. Runs ok without so was just gonna run it till it pukes and go to a different shop next time. Got about 25,000 on it so if it comes close to 100,000 I'll count my blessings and put in another. Still would like some input though if anyone has any. Live and learn.

My 79 Elky has a corvette distributor w/advance curve parts and a new vacuum advance, which was on my 350cu when I purchased the car recently. Now, I dont know what any of this really means... but when I asked the previos owner, he said it was a HEI distributer, and would never need points.

I still have access to the previous owner as a resource, and perhaps I can find out more from him, to add to this post later.

Any feedback from members would be most appreciated..

What does it do when you hook up the vacuum advance? _ Just die?

Have you gone through the process of timing it? If it didn't run from the rebuilder's place then they still have work to do with it. I've got an "RV" Cam in mine. The Comp XE 268. There is no reason that that advance shouldn't work and work properly. Without it the engine can go through too lean a condition and too rich. Even EFI advances and retards timing to suit the engines needs.

You're probably getting poor mileage bad performance. I'd say it sounds like the Cam was advanced too far when they installed it but I could be wrong. It is weird that they shop left the advance disconnected. :mad:

Stevus79,

The HEI uses an electronic module in place of points. That module can go bad just like points. And Just like points your truck will die, or run ragged, sometimes at varying RPMs or just quit running.

The Module over came the weaknesses of the points. But it is still capable and likely to go bad. They will last a lot longer and generally do not require any of the Dwell meters or gapping that the points did. So they are better and most produce more electricity for the spark.

This may be a long shot but where is the vacuum source coming from? In other words, is the vacuum line hooked up to manifold vacuum or is it coming from a ported vacuum source? Straight manifold vacuum is sometimes too much, over-advancing the timing at idle. Ported vacuum comes from a port, usually on the carburetor, that is somewhat regulated, reducing the vacuum signal to the canister. Disconnecting the advance canister should make the rpms drop a little if it is hooked up correctly and not cause the engine to stall when reconnected. In the past, disconnecting the vacuum advance was standard procedure when setting initial timing, regardless of wether it was points or electronic ignition. If you have access to a vacuum gauge, try measuring the amount in the line as it is hooked up now and then check your carb for unused ports that have been blocked and see if any have less vacuum at idle. Chances are that one of them is the right one for your advance canister and was blocked by mistake. Also note that vacuum goes down as you open the throttle (then the weights take over to advance the timing) . Hope this helps somewhat, let me know what you find out.

Thanks ElkyPete!!

Thanks for some input guys. Here's the rundown. Was a boughten shortblock put in at home. All the problems have been fixed but this one and it has many friends scratching there head and shrugging shoulders. Hooked up it hesitates terrible starting out and you can feel a shake in the motor while driving 55 or 70mph (depending on the speed limit 8) ). It's hooked up to the right port on the carb and it does the same thing no matter where the timing was set. Went all through the timing process from 4 to 12 degrees, with different springs and weights and still the same.It flat won't run worth a crap with the advance hooked up. Was wondering about the cam. Found out afterwords that they put in reground. Asked the owner of the business what lift and duration was in it and the reply was " I don't know,we just have them classified as stock or R.V when we get them back" Thats about the time the lightbulb really started to glow. PEOPLE!!!!!, do alot of shopping around and asking questions when motor hunting and don't go for what always sounds like the best deal. Figured I flushed about 600.00 on this. I could go on and on. Only took a week or so to find out a warrenty is only as good as the owners word. In this case ,PFFFFT. 70,000 or 7 yrs. prorated warrenty? Yea right! Right now its running like a mechanical dist. Performance is pretty crisp but I know the milage is suffering a little. Thinking about redoing the top-end, has good vaccum and compression.Bought a BIG jar at a garage sale and putting change in everday, my next motor fund. Thnx for the input guys,appreciate it. Anymore suggestions are more than welcome.

Start over again! Pull the distributor and take it to a speed shop and have them check it out. Bring engine to TDC and then re-install distributor at #1 cylinder. Something sounds like it was installed wrong. :huh:

Did that more than once. New caps,rotors, the whole works. Had it put on a machine and they couldn't think of why. Everything looked good on the printout. It's about tune-up time so probably dink around some more when I get a nice day to spend on it outside. Did anybody else see that thing on Horsepower TV about lining up the spark in the distributer? Might do that check when I do the tune-up. The way they talked it was a good Idea to do all HEI's this way. I'll let ya know how it turns out when done. Thanks guys. The input is great. Finally a site where a person gets others idea's. Keep up the good work. And sorry to say the only speed shop around here is the one where I bought the engine. :-(

Try this first pull your valve cove ,bring #1 up on top dead center by the timing marks look at both valves . Both should be close if not is retarded
or advance. If they are look and see where the dist is pointed. The dist
might be off by couple teeth or blancer is the wrong one. With port vacum
to the dist you advance will curiseing, with man. vacum more low troque
and power up a point. When check the valves also check and see if piston is tdc.

Found out afterwords that they put in reground. Asked the owner of the business what lift and duration was in it and the reply was " I don't know,we just have them classified as stock or R.V when we get them back" Thats about the time the lightbulb really started to glow. PEOPLE!!!!!, do alot of shopping around and asking questions when motor hunting and don't go for what always sounds like the best deal. Figured I flushed about 600.00 on this. I could go on and on. Only took a week or so to find out a warrenty is only as good as the owners word. In this case ,PFFFFT. 70,000 or 7 yrs. prorated warrenty? Yea right! Right now its running like a mechanical dist. Performance is pretty crisp but I know the milage is suffering a little. Thinking about redoing the top-end, has good vaccum and compression.Bought a BIG jar at a garage sale and putting change in everday, my next motor fund. Thnx for the input guys,appreciate it. Anymore suggestions are more than welcome.

The first engine for my 76 was a "Remanufactured Long Block" from a local engine place. I spent 6 bills on the assembly. It turned out to be a POS. When we took it out last November, the rings in #8 & #6 had never seated and were frozen. The Heads were different castings and different years. Some of the valves had been ground down so far you wouldn't even believe it! The head gasket was leaking between #4 & #6. The only thing that ended up being useful to me was the block. Crank, Cam, pistons, rods etc.. all needed to be replaced nothing matched. I mean a POS. It is now a very nice 383. I'll never do that again no more cheap rebuilt engines from "Johnny on the Spot!" sellers.

When doing the 383, I had a terribly time with a piticular performance shop in Dallas. It ended up working out but I am not going back to those people again.

SO do be careful with who you use and what your getting. If it is a performance shop then make sure you know the place well.

it is impossible for the distributor to be off by a couple teeth. It is either in there right or its 180 degrees out. This problem sounds like the distributor is 180 degrees out. take the distributor out, give it half a turn, toss it back in, and then go after trying to tune it. BTW, dont use the ported vacuum initially, see if you can get the vacuum adcance to run off of the manifold vacuum.

This might be a long shot. Do you know what direction the distributor rotor turns looking at it from the top? Where the vacuum advance enters the into the distributor housing should go into the direction of rotation. I don't know if any GM HEI turns counterclockwise or not.... I doubt it. If the vacuum advance mechanism works the same direction as rotation it will be retarding the timing instead of advancing it. All the SB Chevy's I've worked on turn clockwise, as far as the distributor is concerned.

I rebuilt a HEI once and Had similar problems. Does it start with a backfire when the vac is hooked up?

I got a friends hei that i knew worked and found that it was the electronics that you plug in the module to.

Good job 80elcamino, I didn't think of that one! If you bend a wire back and forth enough times, it will break. Same thing that happens with the wiring inside a distributor with the vacuum advance moving the guts around like it does.

I spent a month tearing down the engine to replace the timing chain to find out it was the dist. Which was a 20 min job.
8O