New Distributor Vacuum Advance Issue--any ideas??

matts70 · Feb 5, 2010

OK, so my distributor woes continue. I bought a new remanufactured distributor from Advanced Auto. It's supplied by Cardone, which also supplies Autozone and Rock Auto and lots of other parts companies. Installed and idles fine. Timing is good. Run it up to 3500 RPMs without trouble.

Then, I plugged in the distributor vacuum advance canister to PORTED vacuum on the motor. Idles fine. Hit 1500 RPMs (and above) and it runs awful like it's not hitting all 8 cylinders. Took it back--they replaced it and I got another one. Same problem--runs and idles fine without the vacuum connected, but you plug in the vacuum advance and it runs like crap at 1500 RPM.

Anybody have this happen to them? Is the advance curve so royally screwed up on these remanned models, or is there something else going on? I expect better out of the box.

My only real modification is a 500 CFM 4 barrel and corresponding Performer 289 intake. The old stock distributor's advance worked fine with this carb (bushings were worn out). It's a 1970 with a 302 engine.

Viperwolf1 · Feb 5, 2010

What's the inital timing set at? You should also be able to determine the centrifugal and the vac advance with a timing light. At idle there shouldn't be any centrifugal advance. At 1500 rpm there should be about 3-6 degrees of centrifugal advance. At 5000 rpm there should be somewhere around 11-15 of centrifugal advance. Vac advance should be about 11-15 with over 12" of vac.

302fix · Feb 5, 2010

What is your initial timing setting? If it's > 12*btdc then back it down and try again.
Also check total advance. I'd bet with the vacuum you're just getting too far advanced.

Matt w/70 x2

matts70 · Feb 5, 2010

Initial timing numbers have been off on this thing--I think it's a timing chain/timing gear issue since finding TDC on #1, lining up the 0* timing mark with the indicator, and pointing the rotor to #1 didn't help with the timing mark.

But, using the old vacuum gauge method to set timing and then putting a light on it--it idles at 36*. At 3600 RPM, it jumps to 70*.

Again, the old distributor was running OK with this as far as the vacuum advance was concerned.

302fix · Feb 5, 2010

Also:
The vacuum advance unit must be connected to a port on the the carburetor above the throttle plate which does not have constant (while idling) until after the throttle plates are parcially open (when stepping on gas pedal).

matts70 · Feb 5, 2010

302fix said:
Also:
The vacuum advance unit must be connected to a port on the the carburetor above the throttle plate which does not have constant (while idling) until after the throttle plates are parcially open (when stepping on gas pedal).

I'm definitely running ported vacuum. If I connect it to full vacuum it runs poorly right away and wants to die at idle.

Viperwolf1 · Feb 5, 2010

matts70 said:
Initial timing numbers have been off on this thing--I think it's a timing chain/timing gear issue since finding TDC on #1, lining up the 0* timing mark with the indicator, and pointing the rotor to #1 didn't help with the timing mark.

But, using the old vacuum gauge method to set timing and then putting a light on it--it idles at 36*. At 3600 RPM, it jumps to 70*.

Again, the old distributor was running OK with this as far as the vacuum advance was concerned.

I don't really understand what you're saying about the timing marks but 36 is about 30 too much at idle. The additional 34 degrees at 3600 rpm sounds about right if that counts both centrifugal and vac advance (vac connected).

302fix · Feb 5, 2010

Then you're probably right about the timing chain.

You could be off a tooth on the distributor but a worn out timing chain sound more like your problem. The more it stretches the more you have to advance the dist to catch it up.

The vacuum advance it still a little puzzling though.

matts70 · Feb 5, 2010

Viperwolf1 said:
I don't really understand what you're saying about the timing marks but 36 is about 30 too much at idle. The additional 34 degrees at 3600 rpm sounds about right if that counts both centrifugal and vac advance (vac connected).

I was trying to describe how I set the distributor and rotor in relation to cylinder #1. I may have chosen the wrong words describing the process I used--sorry for the confusion. My main point should have been it idles perfectly fine at 36* reading.

At 3600 RPM, it reads about 72*.

I hope that makes better sense

matts70 · Feb 5, 2010

302fix said:
Then you're probably right about the timing chain.

You could be off a tooth on the distributor but a worn out timing chain sound more like your problem. The more it stretches the more you have to advance the dist to catch it up.

The vacuum advance it still a little puzzling though.

I'm confident the dizzy is where it belongs. I'll look into that timing chain issue--I was unaware of that. Thanks!

302fix · Feb 5, 2010

IS it possible you clipped the timing light to the #5 cylinder instead of #1?
Passenger side front. I've been there.

Viperwolf1 · Feb 5, 2010

Back the initial timing down to about 8 BTC. If it doesn't run there you need to fix something else. After resetting the timing turn the engine over until the timing mark is exactly where you set it (8 degrees). Pop the cap and see which wire the distributor rotor is pointed at. It should be right on #1 or #6, not halfway between the terminals.

matts70 · Feb 5, 2010

OK. Well, there was an allen screw inside the vacuum port--I didn't think about whether there was one earlier. I turned it that little screw IN (clockwise) about 3/4 turn where it stopped tight. That made it worse. I then turned the allen screw ALL the way OUT (counter-clockwise, 6 or 7 turns) until it was tight and now it runs MUCH better.

This is the good news, but isn't this odd? I'm still trying to figure everything out.

Viperwolf1 · Feb 5, 2010

matts70 said:
OK. Well, there was an allen screw inside the vacuum port--I didn't think about whether there was one earlier. I turned it that little screw IN (clockwise) about 3/4 turn where it stopped tight. That made it worse. I then turned the allen screw ALL the way OUT (counter-clockwise, 6 or 7 turns) until it was tight and now it runs MUCH better.

This is the good news, but isn't this odd? I'm still trying to figure everything out.

Stop messing with stuff that isn't broke. You're creating future problems for yourself down the road. You have too much initial timing. You need to adjust the distributor to correct it, period.

matts70 · Feb 5, 2010

Viperwolf1 said:
Back the initial timing down to about 8 BTC. If it doesn't run there you need to fix something else. After resetting the timing turn the engine over until the timing mark is exactly where you set it (8 degrees). Pop the cap and see which wire the distributor rotor is pointed at. It should be right on #1 or #6, not halfway between the terminals.

When I take it down to 8 BTC, it's on the verge of dying. I did change the timing and backed it off a bit--it runs best at 30* at idle. It's running good now. . . but why the 30*?

302fix · Feb 5, 2010

matts70 said:
My only real modification is a 500 CFM 4 barrel and corresponding Performer 289 intake...

Check for vacuum leak at the carb.

Is the vacuum advance unit pointing roughly at 7 oclock.

matts70 · Feb 5, 2010

Viperwolf1 said:
Back the initial timing down to about 8 BTC. If it doesn't run there you need to fix something else. After resetting the timing turn the engine over until the timing mark is exactly where you set it (8 degrees). Pop the cap and see which wire the distributor rotor is pointed at. It should be right on #1 or #6, not halfway between the terminals.

When I take it down to 8 BTC, it's on the verge of dying. I did change the timing and backed it off a bit--it runs best at 30* at idle. It's running good now. . . but why the 30*?

matts70 · Feb 5, 2010

302fix said:
Check for vacuum leak at the carb.

Is the vacuum advance unit pointing roughly at 7 oclock.

No vacuum leaks. Vacuum canister is pointing between 6 and 7.

Everything seems to be running well now, but my curiosity would love to find out why it's so far advanced. . . then again, as Viperwolf pointed out, perhaps just forgetting it and leaving well-enough alone isn't a bad idea either. This can be frustrating.

Thanks!

Viperwolf1 · Feb 5, 2010

matts70 said:
No vacuum leaks. Vacuum canister is pointing between 6 and 7.

Everything seems to be running well now, but my curiosity would love to find out why it's so far advanced. . . then again, as Viperwolf pointed out, perhaps just forgetting it and leaving well-enough alone isn't a bad idea either. This can be frustrating.

Thanks!

I'm not suggesting you forget it and leave it alone. I suggest you set the timing correctly and then find the real problem. That's why you should check the position of the rotor. You should also check the slop in the timing chain. Something is very wrong and it isn't the distributor.

matts70 · Feb 5, 2010

Viperwolf1 said:
I'm not suggesting you forget it and leave it alone. I suggest you set the timing correctly and then find the real problem. That's why you should check the position of the rotor. You should also check the slop in the timing chain. Something is very wrong and it isn't the distributor.

Timing is set where it runs good now. Onto the other issue. I'll check on the rotor position first and post my finding either in this thread, or a new one, depending on how soon I get to it.

I try to post as much info as I can when I encounter a problem and ask for help in case there are a lot of other people like me who use the search function to try to fix their problem in the future.

New Distributor Vacuum Advance Issue--any ideas??

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