Slight miss in my 69 Z28

[sixt9rsx33]

At idle my car has a slight miss/stumble. This issue does not occur above idle or at acceleration. The car will idle at 900 and the tach will drop to 700 or so. The drop is almost undetectable by ear or feel. I hooked up another tach to the car to confirm that my tach was not going bad and had the same result. I suspected bad plug wires those checked out ok. I cleaned the distributor cap terminals. (I have not changed the cap yet, it looks ok). Spark plugs are good. I recently replaced a bad condenser. The points have not been replaced. I was thinking that there may be trash in the idle circuit of the carb since the problem is only at idle. Is this a possibility? Any ideas are appreciated.

Thanks

Lawrence

[earntaz]

First off -- has the carb ever sat without fuel? What I mean is, if the carb has fuel in it after rebuild and then the car sits for an extended period of time -- the fuel evaporates and the gaskets (cork) dry out and shrink. This will sometimes cause issues with idle. You have already said there may be contamination in the idle circuit -- could cause idle issues as well. This is just my perspective -- there are many experts here that may chime in. TAZ

[m22mike]

Lawrence
Can your condition be more of a surging idle up and down ? Do not rule out the vacuum advance can. You might even eliminate it for TS. Might have to temporarily adjust your idle up.
Is it a stock can. # on it ?

Mike

[sixt9rsx33]

Mike,

The idle does not act as if the vacuum hose was disconnected and then put back on the can. But that is a good call. I did not think of that. Yes it is a stock can. Can't recall the number off the top of my head, but I remember chasing the can down based on John Hinckley recommendation. I painted, and did a mild resto on this car in 2009 so the diaphragm could be shot. I will check that out thanks.

Lawrence

[JRSully]

Reach out to Eric at Vintage, the master will solve the issue...

[njsteve]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: JRSully</div><div class="ubbcode-body">Reach out to Eric at Vintage, the master will solve the issue... </div></div>

Yes, he is the Yoda, or more precisely, the Obi-wan-Carb-nobi of tuning carbs. [img]<<GRAEMLIN_URL>>/grin.gif[/img]

[sixt9rsx33]

Yea Eric has helped in the past.

[sixt9rsx33]

Mike,
Pulled the vacuum line off the can last night. Cruised around and seemed to be ok. But when the car really warmed up I had the same problem. Maybe a little exagerated with no vacuum advance? Anyway next step is to pull the carb and poke around and look for issues.

Thanks

Lawrence

[mockingbird812]

Did you plug the vac source for the distributor when you disconnected it?

[starrider]

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.