9.9

[whaledog]

with a 15 hp carburator the 15 motor turns 6,000 rpm rated.
the 9.9 hp motor is restricted by the carburator size turns only 5,000 rpm.
this is a factory stock rated rpm for horsepower.If you raise compression and rpm you will make more horsepower .

[VINTAGEVECTOR225]

thanks,how much can you cut head and still run pump gas?and how far can you advance the timing?

[Skoontz]

Before you just take any random number, find out exactly what the engines clearances are. Remove the head, and take some modeling clay and place it on in the top of the head. Torque the head with the gasket, then remove it. Measure the thickness of the clay using a micrometer. Some heads we have only been able to cut .040, others we cut .100. Depends on what you have.

[one eight-w]

Sounds like we have an unlimited budget. So while we're at it, why not bore it over, port it, ceramic coat, cut the head, balance the rotating assembly, lighten the flywheel, etc. And since it is going back on an inflatable, I assume we need a stock gearcase. Have you tried any different props? There are lots of things you could do, but realistically, the carb change is the only thing you will notice, the rest is, in my opinion, wasting time and money.

[VINTAGEVECTOR225]

thanks,i think i will leave the timing and head alone,the parts break down i looked at had the same part#between the 9.9 and the 15 unless i was looking at wrong,this is not an unlimited budget the guy i am rebuilding was wondering if there was a few things i could do to it to make it run better than stock.he has a 10pitch prop on it and it ran 22mph before the thermostat broke and pluged off the water inlet to the motor and overheated.if this was a v6 merc i know exactley what to do to make it run.the prop book i looked at did not have a prop bigger than a 10pitch.

[Skoontz]

Solas has an 11" pitch stainless prop for a /
'74 and newer (thru hub) OMC for $295.00.

[VINTAGEVECTOR225]

any one have a 15hp carb?

[Skoontz]

make 15HP, why not find a good guy with a flow bench and bore the 7/8" carb to 1", add a butterfly and you got it.... New 15HP carbs are $175 a piece.....

[VINTAGEVECTOR225]

make 15HP, why not find a good guy with a flow bench and bore the 7/8" carb to 1", add a butterfly and you got it.... New 15HP carbs are $175 a piece.....

where do find a 15 butterfly?

[Skoontz]

Get a piece of brass shim stock the thickness you need, and have it machined. Probably about 50-$100.00....Or, start looking at lawn mower carbs, I would say 18-25 HP Kohlers, or Briggs motors. They will have the size butterfly you are looking for, or at least be a good spot to start looking.