Trojan Boat Forum

Hope someone might have some thoughts on this. I dropped the boat in for the new season and took it out for a spin, I had the props tuned over the winter and she ran great. I topped my 1976 F32 with Mercruiser 233's out at 3900 RPM which is close enough to spec for me. I went out fishing for a second day and she ran great for a couple of hours until I started loosing RPM's, by the end of the day I could not get it up past 3000 RPM. I had this problem last year to but was not able to figure it out. I have no problem starting the boat at anytime and it idles fine. I had new Mallory distributors installed last year but that did not remedy the problem. Then I thought about vapor lock but what I understand about that is the boat would not start after awhile and that is not a issue. I also did a complete tune up and adjusted the timing. This is making me crazy, can anyone offer some words of advice, Thanks.

I had a similar thing happen to me check the fuel lines for leaks tighten all the clamps, make sure your fuel vents are unobstructed. My issue was ball valves I installed so that I could turn off one tank and draw from another. The valves were labeled 3/8 but inside they were 1/8 after I switched them out and got rid of the birds nest in the port vent no more problems. Bogging down like that is a fuel problem usually. Replace any dry rotted lines.

I hope this helps.
Wolf

Start with changing the fuel filters

+1 fuel filters

I replaced both fuel filters when the boat went in as I do every year, also both carburetors were rebuilt last year to try to remedy the problem with no success. I will double check my fuel lines which are the original lines. Should I change them to rubber fuel hose? they all seem to be in great shape.

Does it start and run at low speed, 1200rpm then it will stall before you can get it on plane?
If so check your anti siphon valves in the 90 bend on top of tank.... They are likely plugged with crud so reducing fuel flow.

Don't switch to rubber if you don't have to but do re-Teflon (the yellow Teflon not white) all fittings including to the carbs.

+1 on anti-siphon

Hi,The boat starts and idles perfectly. Again, I have no trouble starting the engines at any time. Also, the engines never stall. I also have this issue, the old owner replaced the Rochester carbs with new ones... not Rochester, and in doing so used a shim and / or wedge to make them fit. But I have run the boat for 4 years and only started having problems last year.

A couple of questions----- does this only happen when the engines have got a good heat soak,before everything gets hot do the engines perform as normal----- that is just a spacer under the carbs,probably to keep heat from the carbs ---- if it is heat related look at coils and check compatibility with the ignition system----- are both engines the same???---- Mike

One more --- do you have electric fuel pumps---- is that fitting near the flame arrester not for the mechanical fuel pump vent,not sure on that---

Does the problem reset - ie when you first take it out each time it runs fine, then degrades the longer you run it? Or was it good on first run, degraded on second run, and has run poorly ever since?

If its the first one, it is likely fuel delivery (vapour lock, anti-siphon valve, vents, fuel line too close to heat source), air-fuel mixture (dissimilar metals expanding under heat at different rates causing gaskets to not seal properly, or maybe plugs that are not properly seated (fine when cold, not so fine when hot)) related, or ignition (coil, ignition module, ballast resistor, or aging spark plug wires affected by temperature after a couple of hours).

If it is the second one, I would lean towards bad fuel - check or change the filters again and see if they are still clean. Clean filters only stay clean until enough crap clogs them, and if your tanks have enough gunk in them a few hours of running may be enough to do that.

I have also seen issues with timing being set wrong or distributors that are not properly advancing, but you usually don't see degradation in performance, just bad performance.

Ok, Went out today and she ran good. 3,800RPM was the best she could do. Still not convinced she is running at her best. It was tough to keep the engines in sync. I changed all the spark plugs yesterday and found one that was cracked, other than that they all looked good. I think I'm going to pull the live well / tackle box from under the fly bridge steps and pull the ladder and open up the rear cockpit and inspect the gas tanks, hoses and gas vents. It's a bitch but needs to be done.

A couple of years back, I had this problem after the engines had come up to temp after an hr of cruising. The port side engine would just not get past about 2500 RPM, the other one fine. It ended up being a fuel pump. It was not leaking (pumping anything through the bypass line) but I had tried everything else at that point. New pump, and all was better again.