1998 75 hp Force performance question

[18 Angler]

I have a 1998 75 hp force. I want to know what is the difference between the 75 and 90 horse models. They have the same bore and stroke. The 90 has .1 cubic inch more displacement. I had my carb off cleaning it last year and noticed what looked to be some type of restricter plate. Does anyone know if that is a restricter plate and can I remove it. The 90 horse uses a different spark plug which I believe is just a hotter plug. Does anyone know if this will increase performance and what adjustments may I also have to do. The timing and rpms for both motors are also the same. Any input would be appreciated. Thanks Bob

 

[roscoe]

Re: 1998 75 hp Force performance question

The 90 hp has 3 carbs, and sucks more gas.
It has a different gearcase and spins a bigger prop too.

That "restrictor plate" in the intake is designed to swirl the air/fuel mixture and distribute the fuel to all three cylinders.

Cylinder exhaust porting is likely different too.

 

[18 Angler]

Re: 1998 75 hp Force performance question

Thanks for that info , that answers my questio. Now I have another one. I am looking to get a little more top end. Can I gain some more speed by changing my prop. Currently my prop is a 10-3/8, 13 pitch. At wot I am running about 5000 rpm. at about 26 mph. My boat is an 18' center console.

 

[roscoe]

Re: 1998 75 hp Force performance question

You will probably be able to pick up 2-3 mph with a 11p prop. Better results if you go to a more efficient stainless steel prop.

 

[18 Angler]

Re: 1998 75 hp Force performance question

Can I use a bigger prop also and what will that do for me? I have about an inch and a half bfore it will hit the housing. How about a prop like A Hustler prop? I was on a few web sites looking at props and read a few testimonials from supposed people who bought a Hustler prop and increased top end by 7-10 mph. Do you think gains like this are possible? Thanks Bob