Top end loss of power on 1 engine

[Seif911]

Morn' All,

Since I bought the boat last year, 1 engine has always been lagging and it seems to be getting worse. At ~20 MPH, the starboard engine will be at 4000 RPM's and the port engine will be at ~3000-3200 RPM's. I can give the port throttle a little extra, but it does not speed up hardly any more.

I have rebuilt the carbs, replaced the points and spark plugs, set the idle and set the timing. I just can't seem to gain much here. The centrifugal advance seems loose and flexible. I just found the exhaust cooling system was plugged I. The manifolds and the risers. I also replaced the propellers in the pump.

Any thoughts about what else to look at?

Thanks,
Steve

[waybomb]

Find the specs for the timing at full advance. Then check the timing at whatever the stated rpms for all-in advance. Probably around 24-28 BTDC at 3200 rpm, or some such thing.

If you do not have an advancing timing light or the timing cover indicator does not go all the way to the full advance amount, you will have to buy a tape that sticks to the harmonic balancer that has 360 degrees of markings. Measure the balancer diameter and buy one from someplace like Jegs. Maybe even autozone can get them for you. Check both engines.

I think you alsready replaced the antisiphon valves and blew out the gas tank vents, right? You may also want to replace any fuel hoses after the fuel pump with new marine fuel hoses. Hose gets soft and can collapse under suction. You might not see the collapse because sometimes the hose on the inside fails.

When you rebuild the carbs, you did check the float height, correct?

[Lyndon670]

Steve, what's the temperature on the lagging engine compared to the opposing one?

[Rablackhawk]

Steve - did you inspect your primary fuel filter for clogging?

[Seif911]

Ok, let's see if I can remember all of your thoughts in this reply.
Temperature - oddly enough, the bad engine gets to 160 where the one that works is getting to maybe 100-120
Fuel filter - I replaced the one on the carb and the main one is now a replaceable filter. That one had over a inch of water in it. I dumped that out and put it back on. That was over a year time frame. Apparently the fuel pick up for this engine is lower than the other engine. Last year I pulled a gallon or 2 of water out if the tank. The boat sat for at least 5 years before I got it.
Fuel lines after the pump - are steel.
The float level - well it kind of confused me so I out it back in as it was. I also did not adjust the carbs at all. I just out them back in exactly the same as I pulled it out.
Timing - I just did my other boat from 1968 and did what you just said, I checked it at idle and then at 1500 RPM the advance kicks in and I checked that. I have not done this to the Carver, I will.

[Seif911]

The gas vent - I fixed that last year when I figured out I could not fill the tank properly and as I drove out to Lake Michigan at full speed...both engines died as I just left the harbor, vacuum because of the lack of vent.