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Vette's been driving great all summer, but lately it has developed an intermittent 'miss' where it seems to just lose power for a split second. It often happens on a slight grade uphill and at part throttle but has also done it at full throttle. Usually when I give it more gas also from part throttle. Then this morning driving in to work, after going through first gear at a about half throttle, and letting off to change gears, it backfired! Never done that before. So I don't know if that is a good clue for something to check. I thought maybe it's running rich?
Background on car - engine is crate 350/330 with vortec heads and Comp XE268 cam. MSD dizzy. 4 speed.
I haven't looked at it, I will probably look into it this weekend. Maybe a stuck float? Carb is year and half old Edelbrock 650 which I've had no problems with (so far). Fuel pump I replaced this winter with AC Delco from rockauto.com. What about fuel filter? Should probably check/replace that. I'm thinking the backfire is maybe the best clue of something ?
anyways - thanks in advance for help
Last edited by jim-81; Sep 17, 2015 at 12:48 PM.
Reason: added pictures
Its entirely possible your fuel filter has plugged enough to cause a temporary lean condition which could cause the backfire. If in any doubt about the condition of your fuel filter replace it just to eliminate that as being a possibility.
Its entirely possible your fuel filter has plugged enough to cause a temporary lean condition which could cause the backfire. If in any doubt about the condition of your fuel filter replace it just to eliminate that as being a possibility.
My thought is ignition. Pull the plugs, check for fouling (oil or gas), see if some look worse, replace. Then inspect/ohm out wires, look inside dizzy for obvious problems, rotor, cap etc
My thought is ignition. Pull the plugs, check for fouling (oil or gas), see if some look worse, replace. Then inspect/ohm out wires, look inside dizzy for obvious problems, rotor, cap etc
Me too. Definitely check the above. I don't think fuel would cause your problem.
Great looking engine compartment there Jim. My 81 started doing the exact same thing you described, but I'm still running the stock ECM, actually the ECM on mine just crashed. I have another on order but if it gives me any more trouble I'm disconnecting all of it and going with a Holley carb and a vacuum advance distributor
From: Las Vegas - Just stop perpetuating myths please.
Im thinking things are gettin sticky inside the distributor. A backfire when letting off the throttle is very likely retarded timing. Retarded timing when letting off the throttle would be a lack of vacuum advance (from the vac can).
First i would take a timing light and very u have a timing adv curve from idle to 3000rpm - no need to go higher as thats not good for the motor in neutral/unloaded. BTW with your dist vac line disconnected u should have somewhere like 10 degrees adv at idle to over 30* at 3000rpm. I wound take a look inside the dizzy to verfiy weights are free to move and springs operating. FYI i had all my dist weights freeze up once - no corrosion either, just stuck from lack of use.
Another check u can do if u have a "Mighty Vac" brake tool is verify at what vac reading your vac can starts to move (this is where it drops out) and measure vac where the can is fully extended (full vac = full can adv).
And after all this it could still be the carb. But at least it shouldnt be the dist then. Good luck and nice car.
Im thinking things are gettin sticky inside the distributor. A backfire when letting off the throttle is very likely retarded timing. Retarded timing when letting off the throttle would be a lack of vacuum advance (from the vac can).
First i would take a timing light and very u have a timing adv curve from idle to 3000rpm - no need to go higher as thats not good for the motor in neutral/unloaded. BTW with your dist vac line disconnected u should have somewhere like 10 degrees adv at idle to over 30* at 3000rpm. I wound take a look inside the dizzy to verfiy weights are free to move and springs operating. FYI i had all my dist weights freeze up once - no corrosion either, just stuck from lack of use.
Another check u can do if u have a "Mighty Vac" brake tool is verify at what vac reading your vac can starts to move (this is where it drops out) and measure vac where the can is fully extended (full vac = full can adv).
And after all this it could still be the carb. But at least it shouldnt be the dist then. Good luck and nice car.
Intermittent missing
