BF9 stutters once warm and stops

New poster here. Did a search and a few hits came up but really none with a resolution. I have a used BF 9 on a 12 foot zodiak. Had it a couple of years and in the beginning, ran great. Last fall with 2 people in the boat I was running down the river for about 30 minutes at 3/4 thottle as WOT causes the bow to dig in and actually slows the boat. I tried adjusting the engine angle by putting the pin in different holes but no change. If you get the person up front to lean way back sometimes it gets up on plane, but whatever, thats besides the point. We stopped and had a shore lunch, and on the way back the engine started to stutter, again at 3/4 throttle. It did it once, then like 60 seconds latter, again and then 45 seconds again and the frequency got shorter and shorter till it just finally died. You could start it, it would idle for like 20 sec then die. Thats all it would do. Rowed to shore and pulled it out of the water. End of the season.

Background. That season (spring) I cleaned the carb and noticed what I thought was a clog in some of the little holes in the Main nozzle. So I ordered a new one. Also changed the fuel filter. Dumped out the fuel tank and changed the oil and filter. The reason I did all of this was there was water in the gas from winter storage and so I dug into it a little deeper.

This spring i took the cowls off and wiggled ever wire I could touch or see. The only thing suspicious was the wire on the oil pressure switch felt a little loose. Pulled back the rubber cover and crimped the female connector so it was nice and tight. Placed the engine on a stand in the garage with a water muff on it and ran it like 20 minutes throttled up quite a bit. All seemed fined. Felt like I may have solved the "problem".

First outing this year, engine starts second pull, idles perfect, shifts nice, but once out on the water, same thing. After about 10 minutes that intermittent stutter returns. Then eventually it stops. Fuel system if fine. No water in the gas, lots of water coming out the hole like its supposed to, the green oil pressure view glass is green, squeezing the primer bulb does nothing, more importantly does not help it run. Engine oil level is at the full mark.

So, seems I am not alone with this intermittent very annoying problem.

Anyone out there have suggestions? Or solved this kind of issue?

Any help most appreciated.

Sitting on the dock wondering what to do!

Know nothing about the BF 9, but the vent on your fuel tank may not be allowing air to get into the tank. Take it out and run it with the cap on the fuel can very loosened up. See if that cleans it up.

If that doesn't work, try pumping the primer bulb when it starts to stutter. If that clears it up there is a restriction in your fuel line between the primer bulb and the fuel filter, or your fuel pump may be failing.

how old is engine? How old are the fuel lines,primer bulb, Does bulb pump up firm? When running is bulb staying semi firm? Are fuel lines and or bulb collapsing? Pull fuel line to carb. Squeeze bulb,What kind of flow do you have?

Thanks for your reply.

I have inspected the fuel cap, and as you suggested, loosened the cap but to no avail.

Pumping the primer bulb does change the way engine starts to run, I call it studdering.

The engine is 10 years old. Yes the primer bulb pumps up firm, and its stays semi firm while running. The fuel line is good shape, and are not collapsing. Removing the fuel line at the carb and pumping the bulb results in a nice spirt of fuel.

It just does seem, at least my guess, to be fuel related. Rather, when the engine starts to warm up the whole stuttering thing begins till it final stops. Let it get completely cold, like say 3 or 4 hours and it will start and run like a champ for 10 minutes and then start stuttering and finally stop running.

Weird

Opps to my last reply. Did not see away to edit my last post. I meant to say, it does not seem to be fuel related.

Just for grins, have you tried to run the engine with the cover off? Had a friend with a similar problem. Problem was that exhaust was getting into the engine compartment and starved the engine for oxygen. Just a long shot.

It is also possible that it is overheating and shutting itself down. Pull the thermostat and start the motor (in water or on a hose, of course). Water should shoot out of the thermostat housing.

Thermostat housing could be partially plugged with debris; thermostat might not be opening; or impeller may be damaged.

Mike