Odd missfire @ 1500 RPM
03-17-2005, 11:34 AM
#1
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Car: Still a 3rd Gen
Engine: 450HP 355
Transmission: TH350
Axle/Gears: 9" with 4.11's
Odd missfire @ 1500 RPM
Hey guys, turning to you all for help again...
I've got an odd missfire at about 1500-2K rpm, only happens under load. anywhere above it and below it and the car runs great. I know i need to re-curve the distributor again but it's only been doing this since feb when i brought it out of storage to get the new tranny installed.
Sometimes it will cut out pretty bad at 1500, drop out for a sec, then backfire out the carb.. then run fine. so my thoughts are that it's gotta be a timing issue...
plugs are brand new, wires are brand new, cap and rotor are a year old, coil is about 2 yrs old. Timing should be somewhere around 14 degrees if i remember right.
Thanks for any advice,
Dave
I've got an odd missfire at about 1500-2K rpm, only happens under load. anywhere above it and below it and the car runs great. I know i need to re-curve the distributor again but it's only been doing this since feb when i brought it out of storage to get the new tranny installed.
Sometimes it will cut out pretty bad at 1500, drop out for a sec, then backfire out the carb.. then run fine. so my thoughts are that it's gotta be a timing issue...
plugs are brand new, wires are brand new, cap and rotor are a year old, coil is about 2 yrs old. Timing should be somewhere around 14 degrees if i remember right.
Thanks for any advice,
Dave
03-17-2005, 11:42 AM
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Car: 4
Engine: 6
Transmission: 5
Not a timing issue.
The timing doesn't just up and jump off somewhere from sitting around.
Leave the dist alone. At least, don't start twiddling on the ignition timing. All you'll do is create yourself some extra unnecesary work, for when you fix the actual problem, so you'll have something else you have to go back and undo.
You have a lean condition at that RPM. Probably some kind of gunk washed up into the carb somewhere.
Which, incidentally, is VERY COMMON after a car has been sitting around for a while.
You could try running the car almost out of gas, and then put a gallon of lacquer thinner in the tank when the tank is as dry as possible, then running the motor for a while, and let it sit for a couple of days. Then drive to the gas station and fill it up. If that doesn't do it, you'll probably need to rebuild the carb.
The timing doesn't just up and jump off somewhere from sitting around.
Leave the dist alone. At least, don't start twiddling on the ignition timing. All you'll do is create yourself some extra unnecesary work, for when you fix the actual problem, so you'll have something else you have to go back and undo.
You have a lean condition at that RPM. Probably some kind of gunk washed up into the carb somewhere.
Which, incidentally, is VERY COMMON after a car has been sitting around for a while.
You could try running the car almost out of gas, and then put a gallon of lacquer thinner in the tank when the tank is as dry as possible, then running the motor for a while, and let it sit for a couple of days. Then drive to the gas station and fill it up. If that doesn't do it, you'll probably need to rebuild the carb.
03-17-2005, 12:03 PM
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Car: Still a 3rd Gen
Engine: 450HP 355
Transmission: TH350
Axle/Gears: 9" with 4.11's
well.. i actually built the engine back in '99-00.. and have since put about 4K miles on it. 
a carb rebuild does sound logical
a carb rebuild does sound logical
03-18-2005, 06:27 PM
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Car: Still a 3rd Gen
Engine: 450HP 355
Transmission: TH350
Axle/Gears: 9" with 4.11's
Well, i cleaned the heck out of the carb and tossed in my new curve kit, i used the soft gold springs this time..
i set the timing by ear and she ran pretty good, brought out the light and it was way advanced.. so i set it back to 14 degrees and it runs like an old dog...
at idle under load it sounds like an old beat up chevy truck
anyone care to explain the physics of the timing curve.. that's something i haven't 100% figured out yet. I had the tight springs in there before and it ran pretty good, but now with the gold ones it's all messed up...under load it's got no guts.
I used the kit you can get at AutoZone for $10..
Thanks,
Dave
i set the timing by ear and she ran pretty good, brought out the light and it was way advanced.. so i set it back to 14 degrees and it runs like an old dog...
at idle under load it sounds like an old beat up chevy truck
anyone care to explain the physics of the timing curve.. that's something i haven't 100% figured out yet. I had the tight springs in there before and it ran pretty good, but now with the gold ones it's all messed up...under load it's got no guts.
I used the kit you can get at AutoZone for $10..
Thanks,
Dave
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