What does over jetting and under jetting feel like?
08-18-2015, 01:36 AM
#21
Charter Member # 55
Charter Member
I also have been experiencing a pop through my one carb. I have Holley 850s on gen 6 454s primaries are 72s and the secondaries are 84s, 088 heads, Holley strip dominator intakes with thunder bolt ignition. After I push it on plane, if I run around 2800 rpm I get a pop through the carb, I have also heard a tick which could be pre ignition or detonation but it doesn't happen often usually it shoots trough the carb. If I run straight to cruising rpm (3600rpm) It seems fine. Plugs look good, doesn't appear to be lean, timing is 32 degrees. I'm running E-Top headers, smells fat at an idle, fires right up as the chokes are functional, no bung for o2 sensor. Still trying to find the problem.
08-18-2015, 07:43 AM
#22
Gold Member
Gold Member
You may have a valve train problem on the Exhaust side, maybe a lifter not pumping up on an exhaust valve, weak valve spring, if the exhaust valve doesn't open it will pop thru the carb.
08-18-2015, 08:51 AM
#24
Nasty, I had a very similar issue with my warmed over 454 several years ago. Boat would idle fine, could get up on plane under part throttle, and would cruise just fine at around 3500 RPM. But if I leaned on it at all, it would pop through the carb. I thought it was a lean pop at first, and started chasing problems with the fuel system - replaced fuel pump, etc. Then I started looking at ignition issues, and while the plugs were out I ran a compression test. This revealed my problem - one cylinder only had about 80 PSI - the rest were 130+. Pulled the head and I had a 1/8 inch chunk missing from the edge of the intake valve. This would have been an easy fix, except that chunk was taken off by a big piece of the ringland of the piston that must have gotten hung up in the valve before it exited the motor. When I pulled the other head, I had another chunk of piston missing on that bank as well - on one of the pistons that still had good compression. Detonation rears its ugly head again! Funny thing is, if that intake valve did not have the hunk taken out of it, no telling how long I would have driven around with broken ringlands. Boat was running fine, and no signs of any scuffing in the cylinder walls. Bearings were fine as well.
Hopefully you have a minor issue, but I think a compression test and probably a leakdown are in order to properly diagnose this issue.
Hopefully you have a minor issue, but I think a compression test and probably a leakdown are in order to properly diagnose this issue.
08-18-2015, 09:29 AM
#25
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well I had both engines out over the winter. One engine got a complete rebuild because I spun a bearing, this is the other engine. It ran fine last year however when I pulled the intake I noticed the intake and heads where rotten. So I bought new heads and an intake. I've only run about 10-15 hours this season. I had some issues with crap in the fuel tank, I drained it but haven't had a chance to run it since. My plugs look very clean in both engines but there not quite white or light tan. I'm not claiming to be an expert by any means but I am fairly certain its not a valve train problem. When I first started this engine this year it had no spark so I swapped modules and it fired right up, not sure how I smoked an ignition amplifier sitting on my work bench but it did.
Again thanks for the input guys,
Again thanks for the input guys,
