Have a 78' engine, Edelbrock Performer intake and 750 cfm carb, factory distributor. Timing set at 17 deg advance. Drove it the other night and got on it a few times, and after that I was pretty conservative. Drove it a couple short little trips the next day with no problem. One more trip to the store I noticed when I let off of the gas the exhaust was making a popping sound instead of it being smooth. When I pulled out into traffic, it backfired in the carb and had major power lose. It barely made it up the hill after I pulled out and had to drive on the side of the road because of the line of cars behind me. Gained speed downhill and limped it home. It seemed to me, the more time I drove it the worse it got. My first thought at the time was the timing, due to the backfire. But, it also seemed lean, like a bad fuel pump because it seemed to get worse. So a few days later I replaced the fuel pump and filter. Started the engine and it was backfiring in the carb when pressing the gas pedal down to around half throdle. Then it lost power and died, and would not start again. Thats were i'm at. I have not check the timing since I have to use a buddies timing light, but I will when I get it. I think I can start it if I advance the timing, it seems really retarded.

Any thoughts of possible causes?

 

I had a problem like that once. It turned out to be the roll pin on the distributor sheared and the gear slipped.

 

that is a great suggestion and is very common...my other suggestion is to make sure the accelerator pump on the carb isnt blown, it will cause similar symptoms....

 

The thought of the roll pin on the distributor did cross my mind. Luckily this is not my daily driver. Just a weekend toy. I'm gettiing my buddies timing light tomorrow and check the timing. Also, if I have to I'll swap out the ignition module with a good spare I have. Hoping it is simple and not somthing crazy like a timing chain.

 

Timing chain check:

Pull distributor cap.

Rotate the engine with a wrench until you see the rotor move.

Reverse rotation, and note how many degrees of crank rotation are required before you see the rotor move.

You may have to pull the plugs to do this without busting a hernia.

A lot of slop will allow the timing set to jump a tooth, resulting in either a no start/run or what you are talking about.

Good luck.

 

How many degrees of rotation is too much?

 

The number of degrees slop is the number of degrees your timing is going wander by. So I suppose 10 degrees or more would warrant a timing set replacement.

 

Alright ! Turns out the roll pin on the distributor did shear. Not enough to spin but just turn a bit. Installed my spare distributor and set the timing. Just got back for a test drive and everything is cool. Thanks for all of the input and suggestions.

 

stupid roll pins, always replace them with steel ones, i dont know what else is used but there are some that are too soft...my bro kept shearing his until he used a stronger one....