My car has a Merlin 509 BB, with a Holley Carb. I just started driving it. Now... I noticed when I shut the car off, there is a loud backfire, a puff of black smoke out of the cowell induction... obviously out from the K&N air cleaner.
It doesnt happen all the time. I noticed the same noise and puff on a start up... i think cuz it was cold...
I sounds like a backfire. what is the cause for this? Is this a bad sign for things to come?
Sounds like timing might be a little high.If you are running an automatic trans you can try putting in gear holding the brake and shutting engine off just dont forget to put back in park or if manual trans ease out on clutch to put load on engine and shut it off. hope you can find the problem.
Nobody else has said it so I'm gonna, we need pics. How does it run other than that, also check that there isn't any fuel leaking down the carb from high float levels. Sounds like a timing issue though.
You should put a light on it to see what the timing is doing...
BTW, I had the wires wrong on my cap once, wouldn't run or idle, flames out of the carb run on etc... Moved the wires back on the cap, fixed it.
If it's retarded the plugs/cylinders will be hot enough to pre ignite the fuel.
Sounds like a bad Magnetic Pickup to me. I'll bet it has an MSD Distributor...if it does then you should pull the dist cap off and take a look inside at the magnetic pickup assembly...it's probably all corroded.