Engine losing power

[Xtreme Air]

I have 540 twin engines and the port engine will not go above 3500 rpms. Engine is down 300-400 rpms at idle compared to starboard side. these are the steps that have been taken so far to try to resolve this problem:
1) Compression test. All cylinders are at same compression. No variation.
2) MSD box changed- Same results
3) Plugs and Plug wires changed- Same results
4) Inginition module changed- same results
5) Fuel pump changed-Same results
6) Carb checked and rebuilt-Same result
7) Fuel lines checked to make sure a full line of gas was getting through-same results.
Engine starts and sounds great, but will not make it past 3500 rpm's. Also at 2000rpm's the port engine begins to loose power and throttles must be seperated to keep engine rpm's equal to the starboard engine. HELP! any advise would be greatly appreciated.

[MacGyver]

Distributor slipped? Maybe check the timing.

[fixxxer22]

Inlet restriction in the fuel tank?

[MacGyver]

Two tanks? Bad fuel in one tank?

[MiamiOffshore]

I know you tried a different MSD box but if it's 6al did you use the same rev. limiter chip? I had a chip go bad once and drove me crazy.

[old377guy]

undue friction in port drive?; check fluid in trans and drive, spin prop in neutral. flame arrestor?, accessory drive friction -alternator, circ. pump, raw water pump, Gen. V fuel/water pump combo, serpentine idler,???. switch some parts from starboard side.... good luck.

[MacGyver]

Dead squirrels in exhaust, LOL!

Sorry

[MOBILEMERCMAN]

Inlet restriction in the fuel tank?

That would be the first thing I would check.. Pull pick up tube and inspect... Or run off a remote test tank.

[old377guy]

Dead squirrels in exhaust, LOL!

Sorry

or live ones....smart a....zzz

[Xtreme Air]

Both engines are running off one tank. All lines are filling with fuel. I have not checked the rev limiter yet. Engine does not seem to kick back or run like it is missing. Just have no power after 3500 rpm's. All fluid levels have been checked and drive turns free in nuetral. no difference in port or starboard drive when I turn props.

[MOBILEMERCMAN]

Both engines are running off one tank. All lines are filling with fuel.

It sounds like a fuel restriction. Inspect pick up tubes for obstructions. Most have screens and anti siphon valves. The load the engine sees coming on plane is nearly as great as running wide open.

[imco offshore]

did it happen all at once,,or slowly,,,,,i went back and read your post again,,my vote is you have a set of valve springs laying down,,

[Bradz]

Try disconnecting the rev limter. I have had two do the same thing.

[Chris]

did it happen all at once,,or slowly,,,,,i went back and read your post again,,my vote is you have a set of valve springs laying down,,

It only takes a couple.

[Xtreme Air]

did it happen all at once,,or slowly,,,,,i went back and read your post again,,my vote is you have a set of valve springs laying down,,

boat ran fine going up to Atlantic City. had lunch, came back to boat and both engines started and sounded fine. Went to get on plane, starboard engine ran up to 3000rpm and port engine was lagging behind at 2300rpm. Adjusted port throttle stick to get port engine to 3,000 rpm and had a 4 inch seperation between both port and starboard throttle. Ran compresion check and followed all above procedures at start of post.

[DAREDEVIL]

boat ran fine going up to Atlantic City. had lunch, came back to boat and both engines started and sounded fine. Went to get on plane, starboard engine ran up to 3000rpm and port engine was lagging behind at 2300rpm. Adjusted port throttle stick to get port engine to 3,000 rpm and had a 4 inch seperation between both port and starboard throttle. Ran compresion check and followed all above procedures at start of post.

Maybe u do have a drive /tranny problem, do u run tranny's ???
But i tend to check fuel supply first !

[ATECO ENGINES]

DID YOU CHECK YOUR FUEL PRESSURE. LEAKING EXH WASHING OUT CYLINDERS

[Xtreme Air]

Looks like an exhaust valve due to a bad fuel pump. Fuel pump at idle was pushing 7lbs but with a load was down to 1lbs. Now the real fun starts. Hopefully the piston is still in good shape. Thanks everyone for your help.

[stevesxm]

Looks like an exhaust valve due to a bad fuel pump. Fuel pump at idle was pushing 7lbs but with a load was down to 1lbs. Now the real fun starts. Hopefully the piston is still in good shape. Thanks everyone for your help.

but in your initial post you said the compression was good. if it was lean enough to damage anything you would see that on that test. fix the pump and have a fp gage on it when you run it and it ought to stay at your 7 all the way thru the rev range. as soon as the press drops off that means the moor is running out of fuel either because the pump is bad or the filter is restrcted or the fp regulator if you have one has a broken spring or about 10 other small things... but until you get the fp stable , then its gonna do exactly what you say.

[Xtreme Air]

but in your initial post you said the compression was good. if it was lean enough to damage anything you would see that on that test. fix the pump and have a fp gage on it when you run it and it ought to stay at your 7 all the way thru the rev range. as soon as the press drops off that means the moor is running out of fuel either because the pump is bad or the filter is restrcted or the fp regulator if you have one has a broken spring or about 10 other small things... but until you get the fp stable , then its gonna do exactly what you say.

Yes compression was good in all cylinders. A leak down test revealed a 40% lost in #6. Don't know why it didn't show up on compression test. Valve stem was slightly bent. I will take your advice on fp regulator and continue search. I am only relaying what my engine builder is saying. Thanks for your feedback. It is greatly appreciated due to the fact that there is no better place to be then in open water on a boat you enjoy. Thank-You again.