43L sputtering at 3500rpm

"Just installed a new long blo

"Just installed a new long block 4.3L. I was breaking the engine in and everything seemed to be going O.K. After 45mins it started to sputter at 3500rpm it would drop to about 3000. The more gas I gave it the worse it got. Before the new long block installation, this happened and I replaced the old fuel pump and it fixed the problem. The timing is good just checked it today...any ideas."

First thing I would do is chec

First thing I would do is check all your electrical connections and grounds.

I just bought a boat with twin

I just bought a boat with twin 4.3 V6's and I have the same problem on the starboard engine.
Your symptoms sound very similar to mine. I'm in the process of stripping the engine down. I did a compression check and found there is virtually no comperession between # 2 and 4 cylinders. It looks like the cylinder head gasket has blown in between these cylinders. Easy check is to take the spark plugs out if they are wet and smell of gas and assuming the wires are and plugs are good then there is a fair chance you have a head gasket problem. Do a compression check. You can get a compression tester for about $25 from Walmart

"Kevin, look for a plug wire n

"Kevin, look for a plug wire not seated or out of order and verify fuel pressure. Chk Compression after that. If you find you have blown a gasket, consider these common causes: 1) Non-marine head gaskets installed on the block. 2) Use of old headbolts (stretched) and 3) heads never retorqued after warm up."

I have noticed that the engine

I have noticed that the engine runs fine for 20 or so minutes and then it does the sputtering. Its seems like once it warms up is when the problem occurs.