Slight miss in my 69 Z28

[sixt9rsx33]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: mockingbird812</div><div class="ubbcode-body">Did you plug the vac source for the distributor when you disconnected it?</div></div>

Yes I plugged the vacuum source.

[sixt9rsx33]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: starrider</div><div class="ubbcode-body">hi, are you 100% sure not a plug. does it sound like a single cylinder miss? i know how simple this sounds but i have found many and i mean many times it being just a bad plug.</div></div>

All the plugs are good. Checked them first.

[Alss]

springs on the vacum advance wieghts..did jerry do your dist? had the same issue with a 67 Z..changed one of the springs and it cured the problem..advance was changing back and forth causing a change in idle speed..nagged me for a couple of weeks!

[earntaz]

You may be able to see that with a timing light ... check timing w/light and see if the TDC mark fluctuates ... should be steady. Check spark scatter by checking in total darkness -- raise hood and see if you have fire to ground from the plug wires. TAZ

[sixt9rsx33]

I rebuilt my carb, and still have the same problem. I am glad I rebuilt the carb because the bowls, and the metering blocks had white fine silt/sludge in the bottom of them. I am surprised the thing even ran. Before I rebuilt the carb and even now the engine does not idle good. When I try and set the idle at 1000 rpm it dances above and below 1,000. And when I plug and unplug the vacuum advance it does not respond as good as it should. So I think Mike's theory about the vacuum canister could bare fruit?? Before I do that I will try and test the canister. Stay tuned....

The thing runs like a scolded dog though once you get beyond 1500 rpm.

[sixt9rsx33]

I thought it may be a vacuum leak..acts like it but changed the brake booster hose and still have the problem. I took the distributor off and moved the springs and they snap back, but that does not mean one of the springs is not bad? No Jerry did not do the distributor. I had another guy do it some time ago. I am going to check the timing and see if the light bounces around. If the plug wires are bad wouldn't the car pop at high rpms? Car runs great at high rpm, the idle sucks.

[William]

When you rebuilt the carb did you test or replace the power valve?

[PxTx]

Can you verify what your initial timing, total timing @ 3000 is? How much vacuum advance?

Any chance you could get it on an O-scope and examine the ignition system. You could also use a wide band O2 probe in the tailpipe and dial in the carb too.

The cylinder pressure at low speed is greater than in the upper R's and increased cylinder pressure = increased resistance in the ignition system. Would seem like it ignition related.

[ssl78]

If you hold your hand over the top of the carb and restrict air flow does it die out or does the idle pick up? If the idle raises you could have a vacumn leak.

[sixt9rsx33]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: William</div><div class="ubbcode-body">When you rebuilt the carb did you test or replace the power valve?</div></div>

Yes replaced the primary, the secondary size in the kit was wrong per Eric Jackson so I reused the secondary power valve.