I am running out of ideas. I have a 66 coupe, 289 auto. Once the car warms up I get a backfire out of the exhaust, it is not real loud, but is like pop, pop pop, pop. It usually only happens when I lift off the gas, but sometimes during cruising.

In the last few months I have bought and replaced the plugs, put on brand new Edelbrock 600 carb, new MSD distributor, MSD wires, new exhaust from headers back, and changed the fuel and air filter.

I have adjusted and set the timing on everything between 6-14degrees ( currently it is at 10) and the backfire was the same reguardless. The idle is set at 600 and the carb is adjusted almost perfect as far as I can tell. Any ideas on what to check for next?? Thanks much.

 

You have an exhaust leak - check to make sure everything is bolted down good, and your gaskets are in good shape

 

I think you are right. Since I asked the question, I went and bought a vacuum meter, tested the vacuum and it is good (18 inches), changed the idle to 700, and re-adjusted the carb using the vacuum meter.

When I got under the car, the shop that replaced the exhaust just cut the old pipe off behind the joint where the pipes and headers hook up. So the connection is still the old (rusted) header/pipe. Shouldnt they have changed it at the header and changed the gasket when they installed the new exhaust??

 

sounds like an exhaust leak to me too. You might be able to see where the leak is if you look at all the connections for black soot.

 

they might not have wanted to mess with the gasket cause if it didnt reseal they would be responsible.

 

agree...exhaust leak

 

Any way to tell if it is from the block to headers, or the headers to the pipe??

 

Open the hood and look for carbon stains from escaping exhaust from the surface of the heads to the headers; listen while you rev the engine (don't you wish you had quiet mufflers now); put your hand or a finger and 'feel' hot gasses or even a slight pressure (very dangerous - but effective).
Jim

 

Thanks much to all. I will give that a shot, either way, I guess I am headed back to the exhaust shop. On a different note, the tranny was just rebuilt and it is leaking, so it will be going back to that shop also. Looks like awhile without my car. [&o]

 

I emailed edelbrock, and the tech said to check the float level in the carb. Is it common for the floats to be off?? Adjusting them is not a problem, I am just curious.