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C
I have a 77 that returned to the road today for the first time in 6 years. When she is in park or neutral she revs fine but when she is in gear and is stomped on she does on move very fast and backfires. there is all new plugs and wires just put on last week. any suggestions?
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C
bad auto tranny modulator. It's operated by vacuum from the manifold and if it is not working you may just be drawing air through it and leaning off your intake mixture causing backfires etc.
However, I may be wrong.....
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s
Sure sounds like a clogged catalytic converter to me. Had a Buick do like that and the shop dude cut a hole in the pipe just ahead of the converter and drove the car, the car ran fine, proving the converter needed changed.
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C
I am having trouble finding the vaccum modulator at ecklers do anyone know where to find it?
Thanks
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Former Member
Send PMManteca, CA - USA
Joined: 11/20/2005
Posts: 3623
Vette(s): 1978,two tone,Metalic Rootbeer & gold
1975 L48 4 speed
You can get one at any parts store. No need to order.
Jimmy B.
Just can't wait to get on the road again. 
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Send PMModerator
Duncanville, TX - USA
Joined: 11/8/2003
Posts: 22720
Vette(s): #1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/
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#2-1985 Bright Red/Carmine Cp.L-98/auto
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I don't think the modulator is gonna be the problem. IF the modulator is bad, it will suck tranny fluid up the line into the intake, and you'll see some smoke from the tailpipes. Unless yer trans is completely empty of fluid, it's not adding any excess air into the intake.(unless, of course, the line is un-hooked..) 
I'd be looking into a carb issue...has the carb been cleaned/rebuilt after sitting for 6 years? How about the coil? It could do the same thing, too.
If you drive it easy, does it run ok? A clogged cat. converter will definitely cause it to run sloppy under heavy throttle, usually worse the more throttle you give it.
I'd be looking into a carb issue...has the carb been cleaned/rebuilt after sitting for 6 years? How about the coil? It could do the same thing, too.
If you drive it easy, does it run ok? A clogged cat. converter will definitely cause it to run sloppy under heavy throttle, usually worse the more throttle you give it.
Joel Adams
C3VR Lifetime Member #56 
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"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"
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C
Modulator was just a thought........can't be right all the time. Thanks for the correction Joel.
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B
Had an idling problem once. Idled fine in park, but when I put in drive the car would go dead. Plugged the vacuum line to the EGR valve worked fine. Know it's not exactly the same symptoms. Just might be something you would want to try.
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s
Free Member
Send PMThe Woodlands, TX - USA
Joined: 1/27/2006
Posts: 67
Vette(s): 1969 Coupe, Red, L88 Tribute
Sounds like it could be a firing issue. Sounds like the timing is off or possibly a couple of spark plug wires out of order. I would double check the spark plug wires since they were recently changed. Check the vacuum line to the distributor. Has the timing change ever been changed?
Is there excessive dark smoke out the exhaust when under load? That would point toward a possible fuel issue. Good luck trouble shooting!
Steve
SMSCORVETTE
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C
Thanks for all of the input guys,
With the expection for a new rotor button, wires and plugs everything with the engine is the same as it was 6 years ago. alot of people have been telling me that it is a carb issue. I have put some carb cleaner into the carb and the rest of the can in the tank. I have put 100 miles on her so far and she seems to be getting better. the cat conveters were off before I got her.
will let you guys know of the progress.
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in Forum: C3 Engines, Driveline and Handling
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