Tohatsu 3.5 4 stroke runs poorly

Hello,

I just can't seem to get my Tohatsu 3.5 hp 4-stroke (about 6 months out of warrany) to run reliably for any length of time.

I've had the carb apart several times in the last few weeks. Last time I replaced a questionable gasket between the carb and the intake - replacing that made a big difference. It's a lot better, but I'm still seeing the following symptoms:

After running near wide open for anywhere from 5-30 minutes the engine RPMs drop dramatically. If I leave the throttle open, it'll usually stall. If I drop back to just above idle, it seems to work itself out. Then I can open it back up again and it's fine for a minute or two - or an hour - never can tell. If I run at just above half throttle, it seems to do it less than if I run wide open - this indicates a fuel delivery problem to me, but I'm at a loss. It won't idle reliably once it's started doiing this, either.

I've checked the fuel delivery to the carb - great flow, clean inline filter. The float level seems to be good, the ignition module was just replaced 6 months ago, a new spark plug was installed last week. When I replaced the ignition module I also tilted the engine a bit more than it was, reducing stalling in rough water. I haven't tried tilting it even more, yet.

Any suggestions welcome.

Thanks,

Mark Kaynor

It's probably the angle of the engine on the back of the boat. Move your tilt pin to compensate for the tank angle. About one out of 100 people have an application where the engine angle prevents the carburetor from pulling the fuel from the tank at one tilt setting. Or you could actually have a problem with the engine itself which would require a dealer to run the troubleshoot procedures on it.

TG,

Thanks for the reply. I moved the tilt pin out one more hole, but it didn't seem to make any difference this time.

I'm convinced the big problem is fuel quality. I pull the carb, clean everything, put it back together, and it runs fine. A day or two later, it runs poorly. Unfortunately, the drain plug is frozen in the float bowl, so I have to pull the carb to drain it.

Is it possible to retrofit the MFS3.5A to use an external fuel tank? If I could do that, I could put in an inline water seperating fuel filter on the transom and I bet most of my problems would go away. And I wouldn't have to worry about the internal fuel tank cracking from fatigue due to the heating/cooling cycle here in the tropics like it has.

Mark

Unfortunately that engine does not have a fuel pump so there is no USCG approved or safe way to add a separate fuel tank. You can always throw a new carb at it, but I think that might be a waste of money. There is just enough room between the cock and the tank or the cock and the carb to put an inline fuel filter in place. That would be your best option...The screen built into the cock is only designed to catch large pieces of debris rather than water or smaller junk.

TG,

Thanks again for your feedback. I already considered installing an inline fuel filter, but was hesitant to do so until I'd checked out the possibility of an external tank. I'll go ahead and pick up a couple small ones next time I'm somewhere that has them.

Mark