: Engine misfiring/Kickdown cable
Jan 2nd, 00, 08:33 PM
Ok, I've got something here that had baffled myself, a pretty knowledgeable friend, and a few others. I've got a 67 Camaro with 350ci engine and TH-350 trans with shift kit. The engine is a 72 Chevelle model that I believe still has the original 8.5:1 compression, but has an Edelbrock performer intake, Edelbrock Performer 650 cfm carb with electric choke, full length headers, Comp Cams Extreme Energy Cam, Accell 8mm wires, and stock points ignition. Sometimes under full throttle, it seems to start missfiring. The power goes way down and it will spit and sputter until you let off the gas. If you then punch it again, it'll rev up flawlessly. It's strange, since it only does it SOMETIMES. It'll go two weeks without missing, but then it'll miss at three full throttle starts in a row the next day. The rest of the time, the engine runs perfectly. I don't think it is timing, since I've diddled with it to try to fix it. Plus, I think it would miss all the time at full throttle if it was timing. It has a completely new ignition system in it, with AC Delco distributor, AC points, and AC cap and rotor. I installed the cam in it myself, but it did it before the cam swap too. So, I don't think it is valvetrain related. Please help!! It is embarressing to take my Mustang loving friend for a spirited high speed ride and have the engine keel over on itself and run worse than a lawnmower. You can imagine the Chevy cracks and taunts I get from that. I also have another question...where can I get a TH-350 kickdown cable? My original GM unit got toasted on the headers. Thanks.
PS: If you want to see pics of my car, check out my website at www.geocities.com/MotorCity/Street/5440 (http://www.geocities.com/MotorCity/Street/5440)
[This message has been edited by jrt67ss350 (edited 01-02-2000).]
Jan 3rd, 00, 11:38 AM
Did you replace the lifters when changing the Cam? Also is the mechanical advance on the distributer may be sticking.
Jan 3rd, 00, 12:32 PM
Debris in the fuel line or fuel filter can cause wierd misses that come and go. Try changing filters and checking the carb at the point of entry and even inside the float bowl. If you find some crap in there you may have to check the filter screen at the bottom of the tank pickup and/or just put a big filter in at the tank.
I had a car once that used a phenolic flap in the fuel pump to block backflow - a layer actually split off it and passed thru to the carb where it would settle over a main jet periodically. When the car wasn't running it would float away and therefore wasn't obvious! Took me a while to figure that one out.
Jan 3rd, 00, 12:46 PM
Im looking through your pictures, and it looks like to me that you have your vacuum hose for the advance on the wrong port. It should be on the passenger side. The drivers side is vacuum all the time. The passenger side comes on at about 1100 rpm's. I know it seems like this would be a symptom all the time, but I've seen wierder...good luck Ronnie
Jan 3rd, 00, 12:52 PM
By the way. Most any parts store should carry the detent cable. I bought mine from Autozone. When you start getting into aftermarket components, its basically all the same. I have a 78 malibu, yet my engine compartment looks identical to yours. I have a edelbrock carb, and a 350 turbo tranny. The 78 malibu detent cable will work fine, if you have trouble finding a listing for your car, try the one I've used
Jan 4th, 00, 02:51 AM
Ran into the same problem years ago after putting a 4 bbl carb on a 2bbl engine. Found that the fuel pump worked fine 85 % of the time only under certain circumstances (Wide open throttle) then it would bog out, 72 Chevelle with 8.5:1 seems might have been a 2bbl. also just maybe the lobe on the cam could be worn. On the front of the block( passenger side) are two 3/8 bolt holes, is there a bolt in the upper hole?
It may be too long and draging on the push rod for the pump. It could also have been full of dirt which you pushed into the push rod causing it to stick. Clean it out and make sure the push rod operates smooth, check for full travel, by rolloing the engine over ( by hand) Try a new fuel pump.
When installing the fuel pump, use a long 3/8 course bolt in the upper hole, this will hold the push rod up in place while you install
the pump, replace the bolt with a 3/8 X 1/2 bolt. to prevent oil leaks.
Jan 4th, 00, 03:23 AM
i had the same problem after my last 350 rebuild, but it was spark,do you have points? have you changed your cap, and coil lately, i put on accell cap and super coil and my motor came alive instantly. borrow a buddys to try it for a hour and see if it helps.
Jan 4th, 00, 04:30 AM
Like RockyMtnRacer, I would also look into the carb to see if there is any junk floating in there. Check around the needles that allow the fuel bowls to fill. A small piece of junk could easily make this needle stick open and "flood" the engine with gas. It would act just as you described. Then as the gas continues to stream through, it may dislodged the debris holding the needle open and your car will go back to running fine. Or debris could block a jet temporarily or cause other "hit and miss" problems inside the carb.
I hope you will give us a post if you figure this out as these are the sort of mysterious gremlins that drive everyone nuts! Good luck.