Anyone ever port an outboard?

looks totally different than mopeds, multiple round holes on intake n exhaust sides. I wanna change port timings or should i just square off the holes? Its a two cylinder 9.9 with a single carb. Anyone messed with one?

Re: Anyone ever port an outboard?

Probably Fred /

The only difference between a 9.9 and 17HP, 65, 75, 85hp is the size of the carburetors given the bore and stroke are same, Carburetors make a big difference on an outboard’s HP, porting no so much because the piston and combustion chamber are goofy so for max hp on many 2t outboards different pistons and heads are needed

Re: Anyone ever port an outboard?

Yeah allot of outboards were the same just restricted. I had a 9.9 Nissan and it was the same motor as the 15. Just had to buy a different ramp plate for the throttle. They did that because some lakes and ponds had hp limits. Alot of 9.9s were like that back in the day.

Re: Anyone ever port an outboard?

Pushrod Fifty /

They run at low rpm's and the crank bearings are bushings, but you can see in parts lists from if your engine block was made in higher hp ratings and modify to match the higher rating. Sometimes its only a jet size or blocker plate. The best improvement would be to check that you get full max claimed rpm at full throttle on average conditions for your setup and if the rpm is off, adjust the prop pitch to dial it in.

Re: Anyone ever port an outboard?

An outboard is a totally different type cylinder than the moped engine. Maybe the new ones are different but the ones I had and worked on had the loop scavenge designed cylinders. This is where the pistons, which look way different than a moped piston, had a top to push the intake fuel air mixture to the top of the cylinder and the exhaust was pushed out with what is called a loop flow. Opening up the ports will have adverse effects on the engine. I tried this on a junk engine so many years ago. messed a little with the ports and it never ran after that. I did not even do that much but it was enough to kill the engine.

Just my 2 cents worth.

« Go to Topics — end of thread

Want to post in this forum? We'd love to have you join the discussion, but first:

Login or Create Account