While out cruising yesterday I decided to up the RPM's and shake it out before winter storage and discovered the port gas 454 engine would not exceed 3800 rpm, stbd. engine would go to 4400 which is spec for 454's. I have, in recent past, run both engines up to 4400 with no problem. I welcome any thoughts on what would cause my port engine to top out at 3800. There did not seem to be any noted trouble, engine was running smooth and quiet.
Fuel filter on the slow engine would be a good place to start. How recently did both spin up to 4400? It probably wouldn't be a bad idea to look at the props but if you say it was smooth and quiet they're probably alright. I'm assuming they share fuel or at least were both filled up at the same source? When were they tuned up? Does it rev up to 4400 in neutral? Don't really know but those are some thoughts.
Thanks to all for the advice. I will check all items suggested. I have a sneaking feeling that the cable might be part of the problem as there is a bit of slop in it's movement.
If it has vacuum secondaries (likely) then I would verify that they are opening. Look for linkage problems, sticky butterflies, or other problems with the actuator. Usually it is an easy fix and they just get sticky due to lack of use and "gunk". If the secondaries don't open the engine will usually run smoothly, it just won't make WOT power or RPM. Happens on the `Vette once in a while.
Look down the throat of the carb while advancing the throttle by hand (engine not running). If the secondaries (second set of butterflies) open when you get close to full throttle, then they are mechanical. If they stay closed, then they are actuated by a vacuum device. I would be very, very, very surprised if your engine had mechanical secondaries.... vacuum is the norm.
Scottbee, I checked and no, I do not have vacuum secondaries, pure mechanical linkage. Fuel filters were clean.
I think they are Rochester. A marine mechanic told me boat engines do not have vacuum secondaries because they normally run at a pretty constant rpm verses a car that is constantly changing rpm.
I guess the next thing would be sam356 suggestion to replace fuel pump, checked fuel filter, it is fine.
Probably a Rochester Quadrajet.... a very common carb for the 454 (and smaller engines). In reality, the Rochester does have vacuum operated secondaries. The large butterfly plate above the mechanical secondary butterflies is actuated by airflow and engine vacuum. If it is not operating freely and properly the secondaries won't "work", even if the mechanical butterflies open. Common issue with the Q'jet. Vacuum secondaries on marine engines are quite common. All of my non-fuel-injected engines have had them.
Wow...I'd get me another Mech...I've never seen Q-jets without Vacuum secondaries. But if both filters are clean then I'd check the pump.
I would get a good mechanic that can diagnose the problem and not just a parts changer. Have you checked fuel pressure under load? Have you checked ignition timing and advance? Spark arrestor? etc etc etc......
I don't think the mechanic at my marina has the equipment to test fuel pressure and as is common at marinas they don't allow outside mechanics in. So, to some degree i am forced to do the replace a part routine. I think I will remove the carb and send it off for rebuild and replace the fuel pump. I am also considering having the marina replace the plugs and wires. Even though this is a bit of a shotgun approach it certainly would not be a bad thing for the engine.