neobobstahl
New Member
I'm looking for a small engine mechanic—ideally someone familiar with Mikuni carburetors, especially the BN40i style used on personal watercraft (PWC). This is a dual-carb setup on a brand-new Rotax 787 motor. It ran fine for an hour or two after the motor replacement, but then developed carburetor issues.
This was a new boat for me. Per the seller it had just undergone a motor replacement and some break-in running, and everything seemed fine. I used it for about half an hour with no problems. On the next outing, I stopped for fuel (it's a 1997 model year with a brand-new motor) and planned a longer trip. About an hour into what had been a great ride up the river, the engine suddenly refused to keep running.
So I took it home.
I don’t know much about the injector oil or the fuel that was in it when I got it—only that I was told it was the correct stuff. When I drained about half a gallon of oil, it looked excellent and spotless. I replaced the oil filter and added a fresh gallon of some very expensive specialty oil I was told was required.
As for fuel—well, it’s a 1997—I may have acted on less-than-perfect advice. I was told it could run modern fuel, so I filled the tank with recommended regular gasoline. For all my small engines, I typically use Rec90, and have for some time.
I pulled the carb set off, identified it, and ordered parts. The internals had some rust, sand, and grit—not exactly pristine. No one had mentioned the carbs, but I expected to rebuild them eventually. I cleaned and rebuilt everything, following several YouTube guides. All parts came in the kits except the accelerator pump diaphragm.
After reinstalling the carbs and adding new fuel lines, everything seemed fine. It fired right up. I figured out the cooling hose hookup and got water squirting out the little hole. Ran it for a minute or two, then shut it down. Repeated the start-up/shut-down sequence a few times. I was thrilled.
Rebuilt the carb diaphragms again. Everything looked perfect. Reinstalled them. Drained the fuel system and added fresh Rec90.
Still no start. Spark plugs are soaked—fuel seems to be pouring through. I’ve checked everything I could think of. Maybe I got something wrong—possibly the restrictor is in the wrong spot. I’m hoping it’s something simple. Maybe I misrouted the plumbing, though it seemed to work before.
Wanting to get some use out of this thing before the snow flies, I decided to take it to a shop (and maybe learn something). I called a lot of shops within 150 miles of Youngstown, Ohio. No one was willing to look at it.
Anyone got ideas? I’m currently waiting to hear back from Bear Cycle in Illinois for pro rebuild service, but they seem more focused on motorcycles.
Thanks, bob
This was a new boat for me. Per the seller it had just undergone a motor replacement and some break-in running, and everything seemed fine. I used it for about half an hour with no problems. On the next outing, I stopped for fuel (it's a 1997 model year with a brand-new motor) and planned a longer trip. About an hour into what had been a great ride up the river, the engine suddenly refused to keep running.
So I took it home.
I don’t know much about the injector oil or the fuel that was in it when I got it—only that I was told it was the correct stuff. When I drained about half a gallon of oil, it looked excellent and spotless. I replaced the oil filter and added a fresh gallon of some very expensive specialty oil I was told was required.
As for fuel—well, it’s a 1997—I may have acted on less-than-perfect advice. I was told it could run modern fuel, so I filled the tank with recommended regular gasoline. For all my small engines, I typically use Rec90, and have for some time.
I pulled the carb set off, identified it, and ordered parts. The internals had some rust, sand, and grit—not exactly pristine. No one had mentioned the carbs, but I expected to rebuild them eventually. I cleaned and rebuilt everything, following several YouTube guides. All parts came in the kits except the accelerator pump diaphragm.
After reinstalling the carbs and adding new fuel lines, everything seemed fine. It fired right up. I figured out the cooling hose hookup and got water squirting out the little hole. Ran it for a minute or two, then shut it down. Repeated the start-up/shut-down sequence a few times. I was thrilled.
- Day 2: Starts right up
- Day 3: Starts right up
- Day 4: Cloudy, cold, rainy—stayed indoors
- Day 5: Won’t start. Pulled spark plugs—has spark, has fuel, too much fuel. Plugs are soaked and dripping.
Rebuilt the carb diaphragms again. Everything looked perfect. Reinstalled them. Drained the fuel system and added fresh Rec90.
Still no start. Spark plugs are soaked—fuel seems to be pouring through. I’ve checked everything I could think of. Maybe I got something wrong—possibly the restrictor is in the wrong spot. I’m hoping it’s something simple. Maybe I misrouted the plumbing, though it seemed to work before.
Wanting to get some use out of this thing before the snow flies, I decided to take it to a shop (and maybe learn something). I called a lot of shops within 150 miles of Youngstown, Ohio. No one was willing to look at it.
Anyone got ideas? I’m currently waiting to hear back from Bear Cycle in Illinois for pro rebuild service, but they seem more focused on motorcycles.
Thanks, bob
