[Brian454]

I have a Performance ZZ454 crate motor with about 3k miles on it that i went to start up the other day as the Florida weather has cooled and the perfect time to fire it up. As i was cranking it, the carb shot a deluge of fuel up through the carb and down through intake and backfired. I let it sit and inspected the carb, fuel was leaking around carb. found the diaphragm had a split and caused the issue.
Repaired carb reinstalled and as soon as it started i heard the engine knocking. Thinking this may be unburnt fuel i let it idle for a minute...didn't subside. I shut it down drained oil and checked for metal...none...opened filter and inspected no traces at all. I did engine compression test on all cylinders..all at 165. I changed plugs, changed oil as it smelled of fuel. Started it back up and knocking is still there, when i was cranking engine without plugs in it to visually observe valvetrain movement i did not hear knocking.
Suggestions before i pull the heads ??

 

[Brian454]

My thought process on pulling the heads was to see if perhaps carbon buildup was the issue in a cylinder... a bit of history with this is i had issues with the carb dumping fuel multiple times, fuel actually bubbling in site glasses and dumping after a ride, i changed carbs and then found it was heat related. So this ran very rich.

 

[Brian454]

Thanks for all of the suggestions gentlemen, i will do that this weekend and share results...frustrating as this ran like a scalded dog last time out with no issues. Oil did have fuel in it, as i could definitely smell it when drained.

 

[Brian454]

Great news for me, I got a jump start on your suggestions as it was driving me nuts, I started engine and it was knocking, increased engine speed noise increased. as i was pulling one plug at a time the knocking stopped... It stopped when all plug wires were on the plugs, I went to other side and knocking resumed but intermittent. I continued pulling plugs until through....none made a difference.

I let car idle for a few minutes and noise completely gone... i was baffled, pleased but still baffled, after about 5-10 minutes of idling and working throttle up and down...took it for a ride and its back to its old self. I'm guessing a stuck lifter or hydro-lock or a combination of things.

I wanted to attach the video of noise for others to hear to give others hope that all is not lost when it was knocking like it was.... unfortunately my company laptop wont allow.

Thanks all for your suggestions... i'm still going to borescope cylinders to get an idea what cylinders and valves look like as far as buildup.

 

[Brian454]

You are correct, I know i had flooding, cyl wash prior as i had a bad diaphragm in the carb...found that recently. Luckily my compression did not suffer as i still have 165 in each cylinder. Now that its running and no knock, it is idling a bit rough...did the dollar bill test on exhaust and its sucking in and out on both sides which i know is a sign of a valve issue. Going to get a bore scope and look at valves and pistons.