Slight miss in my 69 Z28

[sixt9rsx33]

Did a few tests today. And I found this to be odd. Had the idle at 900, vacuum line plugged, dial back timing light hooked up, I was only able to get 4* BTDC with the dial on the timing light set at zero. So I was unable to match up the line on the balancer with the 0 on the timing tab. I don't ever recall having this issue with the car. I went ahead and advanced the timing so I could get 4* on the timing light dial with the balancer zeroed out on the timing tab. Took the car for a drive and it spark knocked so obviously too far advanced. I set it back to where it was.
I had 33* total advance at 3000 rpm with no misses or anything weird. The engine purred at 3000 rpm. I also checked the total advance at 2800 and it again was 33*. I did not walk it down to see when the total advance came in.
When I had the gun on the tab at 900 rpm the engine would miss and the timing light would go dark instantly and then come back on. When the light came back on you could barely see that the timing mark was at like 6* or 7* and then come back up to 4* once it stabilized a little. After the 3000 rpm total timing test I set the curb idle back to 900 and the car idled terribly. The tack needle was bouncing all over the place. The other odd observation that I am noticing that very seldom happened in the past is that the car is dieseling when I turn the car off. I never had this issue before. Now about every third time or so when I turn the car off it diesels. This has got to be ignition issue but I am at a loss. I have not changed the points condenser, plug wires yet. I tested the plug wires and they seemed to be ok. I had a condenser go bad a few years ago but the symptoms where different. I guess I better change the points just to cross that off the list? Any suggestions are appreciated.

Lawrence

[PxTx]

How many degrees is the vacuum advance, and is hooked to manifold vacuum?

You are running high test pump gas, right?

[SuperNovaSS]

What is the dwell currently?


Jason

[Plowman]

Did you put a vacuum gauge on it and what did the vacuum gauge say or do{a vacuum gauge would show a broken valve spring}. Also a compression test would help you fine a low cylinder that would only show up as a miss at idle. I hope's this helps.

[sixt9rsx33]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: pxtx</div><div class="ubbcode-body">How many degrees is the vacuum advance, and is hooked to manifold vacuum?

You are running high test pump gas, right?</div></div>

The vacuum canister starts moving the breaker plate at 5.5&quot; and stops at 9&quot;.

Yes premium fuel.

[sixt9rsx33]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Plowman</div><div class="ubbcode-body">Did you put a vacuum gauge on it and what did the vacuum gauge say or do{a vacuum gauge would show a broken valve spring}. Also a compression test would help you fine a low cylinder that would only show up as a miss at idle. I hope's this helps.</div></div>
Tonight I am going to put a vacuum gauge on it and see what it does. I agree that could tell me alot. Should had already done that.

Lawrence

[PxTx]

Good info. When you say starts, is that because you are hooked to ported vacuum?

How many degrees of advance does the vac ad give you?

[Steve Shauger]

I would check vacuum level at idle and compare that to power valve #. I've had to change a power valve because it was too low numerically and it was leaking and opening too soon. It idled poorly and loaded up, and stumbled during initial acceleration. Now the car runs perfect. I was convinced it was a distributor vacuum /timing issue and it wasn't.

[x77-69z28]

This ethanol crap doesn't help with our fuel systems. I started up the Z yesterday, planning on taking it down of the jack stands, and taking it out for a blast on such a beautiful day! Fuel leak at the accelerator pump, and the fuel pump. Shut it off, and put the cover back on.
Buddy

[earntaz]

Don't know if this has been mentioned. With the motor idling, take a can of spray carb cleaner and spray aound the base of carb and in the area of the intake gaskets. If the idle changes -- chances are there is a vacuum leak in that area. TAZ