Rough idle
Thread Starter
Racer
Joined: Dec 2007
Posts: 445
Likes: 2
From: Thomastown Mississippi
Rough idle
1977 Vette/stock 350. Since I bought my Vette last year, I've installed new plugs, plug wires, new carb, set the timing, and replaced most of the vacuum lines. The engine runs great, smooth as silk on the road. It does however idle a little rough, at around 550 rpms. I accidently flooded the engine the other day, and when I opened the hood I noticed that gas had seaped out around the base of the carb and was seaping down the intake. Not a lot, but enough to see it. I'm going to spray some carb cleaner around the base with the engine running and see if it changes my idle. After seeing the gas, I'm guessing that I have a vacuum leak at the base of the carb. If this turns out to be correct, what is the easiest fix. The gasket is only a few months old. I installed it with the new carb. Can you use some type of sealant with these carb base gaskets, that gas won't destroy?? Thanks in advance.
Kenny
Kenny
Team Owner
Joined: Aug 2006
Posts: 24,125
Likes: 15
From: Columbia Missouri
That's a very low idle...seems any engine would run rough at under 600 RPMs. The vacuum leak is very possible. Pull the carb and inspect the carb mating surface and the gasket for any breaks or leaks. The fuel seeping out shouldn't be a problem if the carb is mated securely.
What kind of carb is it and what is your fuel pump...a mechanical or electric?
What kind of carb is it and what is your fuel pump...a mechanical or electric?
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From: Downtown Annapolis, MD. The Future is where we all have to live. Let's not screw it up.
St. Jude Donor '08-'09-'10-'11
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From: Downtown Annapolis, MD. The Future is where we all have to live. Let's not screw it up.
St. Jude Donor '08-'09-'10-'11
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Thread Starter
Racer
Joined: Dec 2007
Posts: 445
Likes: 2
From: Thomastown Mississippi
Yep, same thing. It idles at around 700 in park, and 550-600 in gear. Never stalls, just a little rough. I know it's tuned and timed right, so I'll try idling it up a little. I have to be careful how high I idle it though. On my car anyway, if I idle it too high, it shifts into reverse kinda hard.
Team Owner
Joined: Aug 2006
Posts: 24,125
Likes: 15
From: Columbia Missouri
Yep, same thing. It idles at around 700 in park, and 550-600 in gear. Never stalls, just a little rough. I know it's tuned and timed right, so I'll try idling it up a little. I have to be careful how high I idle it though. On my car anyway, if I idle it too high, it shifts into reverse kinda hard.
That's not the engine's fault though, that's an indication that you have some other drive train wear, and the idle isn't fixing it...just prolonging it.
Check the transmission mount under the car, and have a look at the U-joints. There are six of them.
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Instructor
Joined: Mar 2008
Posts: 235
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From: Waynesburg PA
Mine really just started doing it yesterday. It was alittle over 600 and smooth before. I filled the tank yesterday and drove about 100 miles. Thought maybe bad gas (it was super 93). I was going to try gas filter change (needs it anyhow) and check for vac leak. LMK how if turning idle up alittle helped.
Anybody else have and ideas. DB how can idle be a sign if transmission wear, or did you mean shifting in reverse hard. I shift ok at that low idle.
Anybody else have and ideas. DB how can idle be a sign if transmission wear, or did you mean shifting in reverse hard. I shift ok at that low idle.
Team Owner
Joined: Aug 2006
Posts: 24,125
Likes: 15
From: Columbia Missouri
The idle isn't the sign of wear...the low idle is what the OP did because it eased the hard shift. The loud thunk he hears when shifting into reverse when the idle is over 600 is caused by problems behind the engine. Those problems won't go away because of the lowered idle, and in fact he's maybe experiencing other problems now because he doesn't have a normal idle.