blue thunder

If you do nothing else, do a spark plug reading after hearing the pop. I had a fuel pump volume problem earlier this year and it showed as surging at WOT. Would drop about 200 rpm and come back up, then drop again.

BT

Dennis Moore

Any time you have a problem you need to check the condition of the engine with a simple compression test. They all need to be the same and a warm engine should have at least 155 lbs in each cylinder. The valve springs should also be checked for tension or maybe one is broken.
Narrow it down to a cylinder by inspecting the plugs, it could be a vacuum leak between the intake manifold and heads or underneath the carburetor.
The solid lifter camshaft may have a valve (intake) adjusted a little too tight (when it is hot the valve is hanging open). There is no good reason to run solid lifters on a low rpm marine engine.
Fuel pressure needs to be at least 3 PSI at full throttle
(really, if there is any pressure at full throttle then you have more than the carb can use, right?).
Sincerely
Dennis Moore

alcor

Thanks Dennis & BT, good stuff. I'l be checking those plugs and the compression this weekend. Not sure why the engines had solid lifters but decided to replace them when the engines were rebuilt as they had two different cams (both solid lift ) in these engines. They (the engines) were a real mess once we got into them, crack heads, cracked crane, cracked rod, cracked intake manifold, a piston pin that had drifted into the cylinder wall etc., not sure how they were running as good as they did!

Anyway, I just can't get away from the fact that this exact pop existed prior to replacing everything inside this engine during the rebuild. Makes me keep thinking it's got to be something external. Well regardless, I'm trying everyone's suggestions at this point as none of my thoughts have worked yet. Thanks for the help and I'll let you guys know what I find. Other that this occasional pop, they run great!

Al

alcor

Ok, update on that poping 454. Swapped Distributors, that wasn't it, still pops ocasionally above 3500 rpm. Pulled the plugs (after pop and no idle) and this is what they look like. All of them pretty white except #8 which appears black with a little brown. Any thoughts based on this? Getting gauge to check fuel pressure to see whats happening there, will let you guys know.

Al

Jersey Tom

The plugs are lean. Fuel pressure check alone will not eliminate the fuel pump as the problem. You need a large volume of fuel at 3500 rpm and above. A pump can have pressure but lack volume. Buy a new one or swap with the other one to be sure.

alcor

Thanks for the resposne JT. Local dealer was closed before I could get to them so, swapped the fuel pumps and will try them in the morning. What do you think about that #8 being so dark? Valve adjustment?

Al

alcor

Thanks again Bill. Swapped fuel pumps last night, will try them this morning. Also cleaned plug and put it in another hole, will see what that shows. Changed plug wires last night as well, will check old ones as suggested to see what I find. Thanks again, this ones wearing me out. Being able to swap stuff is at least taking it easy on my wallet.

Al

alcor

FOUND IT! Well them! First, cracked #8 spark plug, second bad wire and third fuel pump, was pumping but apparently not enough volume. Anyway as each one of these were found and fixed, it got better till it was gone.

Thanks a bounce BT, Dennis Bill, Jersey Tom and everyone else that took the time to help out on this one. If you guys ever get to New Orleans look me up. Office 504-887-2800

Al

blue thunder

That's great Al. Now get out there and have some fun!

BT