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1974 rough idle


RCPILOT

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hi Guys, I'm new to to club. Just bought a nice 1974 L48. Having a problem with a very rough idle. Once you get going it runs fine. Last owner just had a major tuneup done and put in new plugs. Any suggestions on what could be the problem? Thanks

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Two Fangs

Could be anything from a mis-adjusted carburetor to a burned valve.

If you are mechanically savvy, we can give some places to get started, otherwise there are many shop owners who post on here that could take care of you, I'm certain.

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As everyone on this forum knows, I am not mechanically inclined at all. However, years ago I had a 71 that ran rough, especially at idle. Finally had the carb rebuilt and it came to life. Probably not your problem, but you never know. My best advice, take it to Bromley's. He loves C3s.

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My first thought is a leaky well-plug on teh Rochester Quad. Any black smoke out of teh pipes?

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No smoke, oil pressure is good. My first guess was something in the electrical system, plug wire maybe?

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I'll take a dip in the pool

vacuum advance issue..........and call Doug! :lol

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plug wire maybe?

Possible.....or maybe firing order. 1-8-4-3-6-5-7-2

I've seen ignition modules do this too.

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Generally you may find a vacuum leak .... or a simple as a chock adjustment .........

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Guest badbobs95

Ls swap it..... Or contact broomleys he knows them the best.

I concur! Call Doug at Broomley's. I mean Bromleys. :laughing gut bustin::laughing gut bustin:

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Final Effort

Somebody stuck a 3/4 race cam in it.

If near Chandler, Bromley

If near Peoria, AZmoterhead

both are Ace members.

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When at idle, sounds more like a full race cam !! Intake manifold leak? Hope it's something simple or I got stung on this car.

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I agree with everyone else - take a quick trip by Bromley's and you'll have EXPERIENCE at your fingertips! And I bet you'll be VERY happy with his service and the interest he takes in advising you on your new baby!!

Keep us posted!!

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RCPilot - As has already been mentioned, it does sound like a vacuum leak of some sort. Have you looked around the carb/intake for a loose hose or open vacuum port? Do you have a 'Mity-Vac' where you could double check the diaphragm in the vacuum advance canister?

Mike T.

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Buccaneer

I disagree with having Bromley's work on it...Put a Crossfire on it and call it a day. :bolt:

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Bromley's Corvettes

Like most have said sounds like a vacuum leak:) Thats first place I would look. How do the brakes feel and head lights work. Is brake peddle very hard or headlights open slow? Sings of a vacuum leak. Also sticking float I would take air cleaner off and make shore choke plate if open.

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Had a mechanic friend look at the car today. Pulled off the valve covers to discover some of the valves not opening all the way. FLAT CAM !! Carb ok, vacuum ok, ignition ok. Having new cam and lifters installed, new belts, front end bushings, also found radiator leak to be repaired or replaced. Ouch ! Not a cheap day. At least when all is done I hope to have a reliable car. I was warned classic cars are money pits! Hey joe@cpr.com , still want to swap !

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Bromley's Corvettes

That sucks but good time for some up grades. Depending how bad cam and lifters are may need to do more then just flush engine out. If lots of metal been going through it bearings will look like crap. What cam you planning to run? What are your goals with the car?

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Buddy says installing a aftermarket mild cam about 25 degrees more lift. I'm an old bird. Goal is to drive car to corvette outings, meet some new folks and have fun. Wanted to go to BBQ Saturday but not going to happen this time. Looking forward to the outings with the Corvette group and Classic Car club in Gold Canyon where I live. Probably won't be much til fall. To hot for most people. Not me. I love AZ and even the summers !

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If that cam is indeed flat .... you'll certainly want to check those bearings ..... that metal had to go somewhere .....

as Doug said ... it may (will likely) need more then a flush ......

I went through 2 flat cams in my C3 ... the second after a rebuild .... it was amazing how bad the bearing got tore up .... had to do a bottom up UGH !!! AGAIN!!!

Easiest test is to pull your oil filter ... cut it open and check it out ...... short cuts can be costly ......

Good Luck with your project ............

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Buccaneer

OK, you do know that I was kiddin'...right? :P

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OK, you do know that I was kiddin'...right? :P

Of coarse I do. Thanks again to all who have made suggestions. I have paid attention and will heed the advice. Hope to have the car at one of the Corvette outings for you all to see. Look forward to meeting the members. Will keep you posted on progress.

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RC - Sorry to hear about the flat cam issue, there's a good chance the previous owner knew about this. You've been getting good advice about flushing out the engine before putting in a new cam and lifter set. When the cam lobes go from oval to round, the removed metal goes everywhere. I know this isn't what you were expecting after just having bought the Vette but take your time and figure out the cam specs you want based on your driving, gear ratio, etc and in the end, it'll just be like the old commercials...'New and Improved'. Good luck.

Mike T.

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