C2 Engine backfire

[Mark F.]

Recently acquired a '65 with a CE 402 engine equipped with a Q-Jet carb. The car had been sitting for five years. When it initially started, it ran fine to 3000 rpm, which is as far as I was willing to take it.

On the second day of my ownership, I noted a backfire through the carburetor whenever I would depress the throttle above a crusing speed. In other words, at 60 mph it ran fine, but when I accelerated it would backfire throught the carb.

I changed the plugs, points, and condensor; no help. Friends opine that the cam has gone flat, or there are intake valve/spring problems.

Any opinions as to the problem are, as always, greatly appreciated.

[Roy Braatz]

Re: C2 Engine backfire

As you add power a miss is usley a spark plug or plug wires.

[Duke W.]

Re: C2 Engine backfire

If I assume correctly that the backfire occurs just as your depress the throttle part way and then the engine picks up and accelerates, it's probably a transient lean condition. A larger pump shot might be the answer.

Try to find out what engine the carb was originally calibrated for. If it was a smaller engine, the pump shot might be inadequate. Also, the manifold could be a factor. A large high rise or single plane will need a bigger pump shot than a more conservative production type manifold.

Also check the ignition. With a dwell meter installed, rev the engine up high and check for dwell variation. If it's more than 2 degrees the distributor needs a good overhaul and blueprint.

Duke

[Clem Z.]

Re: C2 Engine backfire

sounds like a cam lobe gone to me if it backfires at full throttle thru the carb. run a compression test or take off the rocker covers and spin the engine to check the valve movement

[Wayne C.]

Re: C2 Engine backfire

May simply be that the accelerator pump has failed... worked OK at first, but broke after some use.

Also check that the distributor centrifugal advance mechanism is moving smoothly... a little lube might help.

And check to make sure the timing is set correctly... that the base clamp hasn't loosened.

[John R.]

Re: C2 Engine backfire

Wayne may be right as I had the same problem with my 67 L36 last month. Turns out the accelerator pump was inoperative. I can't believe how well the car runs after replacing the pump and cleaning the carb.

[Rich G.]

Re: C2 Engine backfire

It could be a lot of things as others have said, but for what it's worth I had a similar issue with a 66 L79 I got in september. It had been sitting for over a year. After a few days and a hundred miles, the backfiring thru the carb went away. It has run great since. I would check the easy things and drive it a little more.

Rich Giannotti

[Mark F.]

Thanks, guys, for your quick responses. *NM*