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Backfire through carb

jenkx

Well-known member
Joined
Jul 11, 2015
Messages
49
Location
Michigan
My 82 C3 with crossfire injection is popping through the carb. It runs smooth during idle and low acceleration, but under torque or high rpm the engine runs rough and shows a compression backfire with no flames through the carb.
My thought... intake gasket, lifter, head gasket.
Any thoughts please?

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gmjunkie

Well-known member
Joined
Nov 11, 2004
Messages
4,519
Location
Old Fort NC/Vero Beach FL
Corvette
03 Z-51,78 L82 Coupe
Well,First off those are not Carbs,They are Throttle Bodies...……… Big Diff!
My guess is you have some linkage ware and they are out of sink!:thumb
 

jenkx

Well-known member
Joined
Jul 11, 2015
Messages
49
Location
Michigan
Thanks for the reply.... I'm old school with the carb description. :)
I was thinking it would be serious as in gasket.
Do you know a formula for checking.
Visually it looks good.
Thank you so much

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gmjunkie

Well-known member
Joined
Nov 11, 2004
Messages
4,519
Location
Old Fort NC/Vero Beach FL
Corvette
03 Z-51,78 L82 Coupe
Cross fires were never my kick,I know just enough about them to set them on fire!:thumb

[FONT=Verdana,Arial,Tahoma,Calibri,Geneva,sans-serif]https://www.corvetteactioncenter.com/forums/members/wishuwerehere82.html
Send Pete a message,He has one and has managed to keep it going for years. He's purdy knollagable on them!:thumb[SUB][SUP]<strike>
</strike>[/SUP][/SUB]
[/FONT]
 

navy2kcoupe

Well-known member
Joined
Dec 16, 2006
Messages
799
Location
West Central FL and SE Mass.
Corvette
2000 Navy Blue Coupe A4 Z51
Could also be a broken intake valve spring. Had one of those on an L78 396 Chevelle that acted JUST the same way as yours. Easy to check by pulling the valve covers and visually inspect (closely) all the springs.
Andy
 

jenkx

Well-known member
Joined
Jul 11, 2015
Messages
49
Location
Michigan
Could also be a broken intake valve spring. Had one of those on an L78 396 Chevelle that acted JUST the same way as yours. Easy to check by pulling the valve covers and visually inspect (closely) all the springs.
Andy
Thank you for the response.
I just did a compression test and all cylinders were close.
The heads were my first thought. Someone mentioned a piston pin.
I'm probably going to pull the heads and have them resurfaced.

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82ed

New member
Joined
Jan 1, 2020
Messages
3
Location
Herminie Pa
Corvette
1982 silver 2007 white base coupe
In 1988 my 1982 crossfire corvette was having engine issues I had the heads milled and a valve job done on them the compression was 140 pounds per cylinder last year my car started detonation through the throttle bodies it ran good cold but when the car warmed up I had the issues. I checked the compression and it was still 140 pounds per cylinder. I took the car out today and have put on 250 miles with no detonation. You may want to try to run the car in a dark garage to see if you can see any sparks. make sure you have fresh gas in car put a fuel pressure gauge between throttle bodies I had 9 psi check timing disconnect the brown wire I believe it is 6 degrees btdc but that information is on your emission sticker. check or replace sparkplug wires cap and rotor and fuel filter. you can spray carb cleaner around the intake manifold for a leak. In 1982 there was a short wiring harness that went from the starter to the main harness both the male and female connection on my car were bad when this connection came loose the car would not run. I even replaced the module pick up coil and coil.
 

jenkx

Well-known member
Joined
Jul 11, 2015
Messages
49
Location
Michigan
In 1988 my 1982 crossfire corvette was having engine issues I had the heads milled and a valve job done on them the compression was 140 pounds per cylinder last year my car started detonation through the throttle bodies it ran good cold but when the car warmed up I had the issues. I checked the compression and it was still 140 pounds per cylinder. I took the car out today and have put on 250 miles with no detonation. You may want to try to run the car in a dark garage to see if you can see any sparks. make sure you have fresh gas in car put a fuel pressure gauge between throttle bodies I had 9 psi check timing disconnect the brown wire I believe it is 6 degrees btdc but that information is on your emission sticker. check or replace sparkplug wires cap and rotor and fuel filter. you can spray carb cleaner around the intake manifold for a leak. In 1982 there was a short wiring harness that went from the starter to the main harness both the male and female connection on my car were bad when this connection came loose the car would not run. I even replaced the module pick up coil and coil.
Hey thank you for the reply and info.
I appreciate your time.
I did do everything on your list except the fuel pressure.
Visually the throttle bodies look as if the fuel supply is plentiful.
Someone mentioned that the intake gasket might come loose under the center plate on the intake manifold. Of it did it will cause a clapping sound.
Another person said they has a valve spring problem. That will be on the list too.
Thank you again.

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