Recently, my '67 327/300 has developed a rough idle. It can best be described as a "lopey, racing cam idle", not a dead skip. The engine is, of course, bone stock. What could be the problem?
Don
Don
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Re: C2 Rough Idle
Hi Don! We could make a list as long as your arm with the possibilities. A lot of guys around here are trying to get their car to make that sound. Maybe you could help them out!
Seriously, I would start with a good old fashioned tune-up, the usual plugs / points / condensor / distributor cap / rotor. If that doesn't cut it, then we can start to get creative. If you've already been there, done that, make sure your timing is on, try checking your air and gas filters, and maybe start to look around for a vacuum leak.
Have fun!
Pete -
Re: C2 Rough Idle
1. Check point resistance, dwell angle, and secondary ignition components
2, Check vacuum advance for proper operation. (Total idle timing s/b about 25 degrees)
3. Check for vacuum leaks
4. Go through idle speed and mixture adjustent procedure.
5. If above does not cure the problem conduct a cylinder balance test then compression and/or leakdown test
DukeComment
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Re: C2 Rough Idle
Don:
What RPM? The 300 HP engine normally idles about 650 neutral. Could it be that your vac advance hose is cracked or disconnected? Or the diaphrgm is ruptured?
JoeComment
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Re: C2 Rough Idle
Don,
Could be that your Holley carburetor base plate and metering block surfaces are warped slightly and gas is leaking into the engine. I had this problem with my 3810 Holley after the car sat for some time. Check the archives for alot of discussion on this topic.Comment
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Re: C2 Rough Idle
Recommended 300 HP idle speed is 500 in neutral for manuals; 450-475 for PG in Drive.
DukeComment
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Re: C2 Rough Idle
The power valve in your Holley may have ruptured. Put a finger over the front verticle vent, if your car dies right away, the power valve has failed. At idle the power valve is held closed by engine vacuum, if the valve is not able to hold vacuum it will be open providing to much fuel.Comment
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Re: C2 Rough Idle
A vacuum leak can cause a rough idle, such as a leak in the PCV valve hose.Comment
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Re: C2 Rough Idle
Duke;
I should have checked the Manual before shooting from the hip. My first thought, before I read your first post above, was that the vac advance somehow went away, causing the lumpy idle. As you indicate, that engine will turn quite slow without stalling, because of the mild cam. So I am thinking that it is turning maybe 400 RPM with disabled vac advance.
Start with the easy stuff first.
JoeComment
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Re: C2 Rough Idle
and don't forget as part of a complete tuneup to start the car at midnite in a dark garage to rule out ignition wire sparks. i was shocked to find three of them [true, even if it is a bad pun].Comment
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