Motor Problems

[Hammer]

I have an old 40 horse Johnson on my old 15 trihull that is still giving me some problems. I took posession of this old boat and motor 2 yrs ago having to replace the transom and a few other problems. Everything has worked out fine except the motor, which continues to die out at high rpms and the fuel bulb goes slack.I had the whole tank and fuel bulb and exterior fuel lines replaced and it seemed to help but it still has this issue and I have to either pump the bulb or run at low rpms. Anyone got any suggestions?

[FUTCHCAIRO]

TRY RELEASING THE CAP ON YOUR FUEL TANK, I HAD THIS PROBLEM MANY YRS. AGO AND IT TURNED OUT I HAD THE CAP ON THE FUEL TANK TO TIGHT AND IT CREATED A VACUMNE ON THE TANK. RELEASED THE CAP A 1/2 TURN AND NEVER HAD THE PROBLEM AGAIN. YOU CAN NOT WEAR OUT THOSE OLD 35 & 40 ENGINES.
PA
SEMPER FI

[onefishtwofish]

What do you mean by slack? When my boat ran with the vented tank closed, it would collapse the bulb. Looked like someone was squeezing on it. You sound like you are having the opposite problem, there is not enough suction pulling the fuel or you are pulling air. Check your fuel pump gaskets maybe, Maybe a fitting that is pulling a pinhole of air? We just had a nightmare with our 9.9 caused by a bad bulb disintergrating from the inside. Got that fixed and found the fuel pump gasket rotted and shedding rubber to the carb too. Would idle, but would not run under load. Have you cleaned the carb?

[wevans]

There is a screen on the fuel pump also, that can become clogged and not allow enuff fuel to pass. I would get a kit for the fuel pump "usually less than $10" and if that don't fix it, rebuild the carbs "fairly easy on the older motors" seems you've already replaced everything up to the fuel pump already

[DixieReb]

I hate to hear about your problem, I had similar problems with my 2000 model 40 HP Johnson. I replaced all the lines, fittings, bulb, and tank and it helped for a while but came back one day on the water. Ended up having to replace the fuel/oil injector assembly and that got it going again. But it cost me $500.00 to replace, hope that's not what yours needs.

[CSMarine]

Just went thru that with an older 35hp Evinrude. Replace fittings at tank and motor and lines with all new when I redid the engine. Turned out to be a bad fitting on the tank, right out of the box, but still faulty. Replaced it and everything worked fine. The way I found it was that I put pressure on the tank fitting, and hose connection. Just pushed on it sideways while it was running and about to die. When I put pressure on the side of the fitting it would catch back up and run smooth. It does sound like the diaphram in the fuel pump also.

[Hammer]

All these sound like great suggestions. Thinking I will start with the fitting on the tank and then move on to the fuel pump diaphram. Thanks