1998 Force 75

[ShaWinters]

I have a problem that I believe is a multitude of problems.<br /><br />I have a 1998 JC 20' Suntoon Pontoon boat with a 75HP Force. When I purchased the boat and had it rigged, I immediately had a few problems that my dealer had no idea how to solve.<br /><br />First I had cavatation problems where I would be going at full speed, approximately 18-19mph (about 5200 rpm) and it would just about stop, but the motor would surge to about 6500 rpms. I had to shift to neutral and start back up. The second problem was the plugs would foul after about 5-8 tanks of fuel.<br /><br />I did as much research as my limited knowledge would allow and was told a couple of things. To solve the cavatation problem, I first changed to a bigger prop and also put a cavatation plate on the motor that was made by Sylvain. To fix the fouling problem, I was told to switch to a quality outboard motor oil such as Honda or Johnson. Since I put the bigger prop on, I now max out at about 4300-4500 rpms and from what I understand, the range is about 5300-5500. My top end speed is about 13mph and it fouls as bad or worse than ever.<br /><br />The bigger prop and plate took care of the cavatation problem but the fouling problem continues. I have since been told to do a couple of different things, including buy a new motor. I would like to continue to use this motor if possible. The general consensus has been to go back to the original prop, which would allow the motor to breath better. Since its not breathing, its loading up, hence fouling the plugs. Additionally, I have been told to check the fuel pump.<br /><br />Any insight would be greatly appreciated, and sorry for the long winded message.

 

[rickdb1boat]

Re: 1998 Force 75

ShaWinters <br /><br />First thing is to go back with the orignal prop, or even better, lower the pitch of the original prop by 2 or 3 inches and have some extra cupping added to make it bite the water better. That should cut down on the cavitation. Also, where is the cavitation plate in relation to the bottom of the toons?(Higher or Lower) I would run it at 5300-5500 RPM's, which would reduce fouling due to the motor lugging at below optimum RPM's. Doubt it has anything to do with the fuel pump, as it seems to run right up to high RPM's with the original prop.<br /><br />Also, have you decarboned the motor lately? If not, you should try that along with the other ideas. force motors are notorious for carbon build up in the cylinders.<br /><br /> Decarb

 

[steelespike]

Re: 1998 Force 75

I sure wouldnt put too much money into that motor<br />I have an 18 ft toon with a 50 evinrude and it<br /> easily does 20 mph and possibly more.<br /> The fuel pump diaphram may be bad leaking fuel into the engine.The motor trim could be causing <br />cavitation as well.When set right my boat almost never cavitates but if I trim out only 1 notch<br /> it becomes comepletely un usable.<br /> Go back to the original prop and try again.

 

[9675hpforce]

Re: 1998 Force 75

That engine will push your boat 25mph I found that Autolight plugs work better guess there is more electrode. You have a fine engine dont let people tell you other wise I think yours is a mercury in 98 with 3 carbs. Try proping down or up depending on the rpms you are running. Husler props work for mine and cheap.