Poor performance and backfires
03-11-2018, 06:15 PM
#1
Poor performance and backfires
I have a 77, HEI distributor, 350/290 new crate engine. When I start the car it seems to run fine, but after about 10 minutes of driving it starts to run rough, if I floor it I don’t get the power response, it will go to about 3000 rpms and run rough until I remove my foot from the gas pedal, which is followed by a backfire. Every now and then it will accelerate nicely, but the majority of the time it won’t. I did have a FiTech EFI on there but I switched back to a carburetor to trouble shoot.
Ive replaced:
Distributor cap/rotor
ignition control module
coil
vacuum advance
mechanical advance
Spark plugs
Any ideas?
Ive replaced:
Distributor cap/rotor
ignition control module
coil
vacuum advance
mechanical advance
Spark plugs
Any ideas?
Last edited by DavidNHarris88; 03-11-2018 at 06:17 PM.
03-11-2018, 06:24 PM
#2
Could be bad cats.
03-11-2018, 07:00 PM
#4
Racer
Check the cats/exhaust for restriction.
if that is not it, and it is doing the same on FI and carb, and if timing is set right, you could have a wiped cam lobe....
Is backfiring through carb or exhaust?
if that is not it, and it is doing the same on FI and carb, and if timing is set right, you could have a wiped cam lobe....
Is backfiring through carb or exhaust?
03-11-2018, 08:20 PM
#5
Le Mans Master
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Tell us about your fuel filter. Where is it at? In carb? In line? How old?
Ever run around without the air cleaner? Then you can see what the choke is doing easily.
Ever run around without the air cleaner? Then you can see what the choke is doing easily.
03-11-2018, 09:24 PM
#7
03-11-2018, 09:26 PM
#8
fuel filter is in the line and brand new. Just put a brand new electric choke on it and set it today. No luck
03-11-2018, 09:28 PM
#9
03-11-2018, 10:17 PM
#10
Racer
if it idles OK, check your timing, and then put a vacuum gauge on it and see if the needle is steady, and in the correct range for the cam.
When checking the timing, make sure the Distributor hold down is tight (make sure the timing is not "walking" under load because the hold down is loose).
you can also take the valve covers off and turn the engine over by hand--note the rockers, and make sure all are opening and closing properly...
what fuel pump are you using? FI requires much higher pressure than a carb (did you also change fuel pumps when you tok the FiTech off the car and added the carb)?
When checking the timing, make sure the Distributor hold down is tight (make sure the timing is not "walking" under load because the hold down is loose).
you can also take the valve covers off and turn the engine over by hand--note the rockers, and make sure all are opening and closing properly...
what fuel pump are you using? FI requires much higher pressure than a carb (did you also change fuel pumps when you tok the FiTech off the car and added the carb)?
Last edited by keithl1967; 03-11-2018 at 10:19 PM.
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rickimvette (03-14-2018)
03-13-2018, 09:57 AM
#12
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03-13-2018, 10:26 AM
#14
Le Mans Master
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When modges start to fail its either completely Off or completely On circuit. Seldom anything in between. The coil is another story.
03-13-2018, 02:58 PM
#15
Drifting
All modules I've had go bad by running rough above idle when they get warm. All still run in what looks like a limp home mode. I've had the pickup coils fail and they just stop the car period.
Dave
Dave
03-16-2018, 11:01 AM
#18
Le Mans Master
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Good!!!
Problem # 1977350290-DH88 issue solved.
That will be $119. How would you like to make your payment?
Problem # 1977350290-DH88 issue solved.
That will be $119. How would you like to make your payment?
Last edited by HeadsU.P.; 03-17-2018 at 11:20 AM.
