Force Top RPM question & a long story

[hndiman]

I recently bought a 17 ft Starcraft with a 90hp Force, (the boat is rated for 125 hp).<br /><br />The boat sat for about 6 months with no use, the engine starts easy and runs fine (great actually) but tops out at 4200 RPM. Plugs look even, but black and wet (cold and rich).<br /> <br />I have done the following with NO change:<br />19 inch prop to 17 inch<br />set timing and carbs<br />new plugs<br />new fuel lines<br />checked compression 125 #1, #2 & #3 135<br />inspected carb bowels, looked clean no sign of gum.<br /><br />rebuilding the fuel pump &/or re-hosing the gas re-circulation system did seem to add 200 RPM<br /><br />I also installed a new theromstat and a temp gauge and found the engine temp drops below 100 degrees as soon as the engine speed picks up (above 1800 rpm)<br /><br />Anybody have any thoughts?<br /><br />Thanks<br />Ed

 

[Fouled Plug]

Re: Force Top RPM question & a long story

I almost wonder if the fuel tank is venting properly. The 2" pitch change on the prop added zero RPM's? Very interesting.........

 

[hndiman]

Re: Force Top RPM question & a long story

fouled plug<br /><br />I agree about the 2" pitch change, i found a friend with a 15" and I am going to put that on for the hell of it....I wonder about the temp...with the engine running below 100 degrees could it affect perfomance that much? <br /><br />I will look into the tank venting <br /><br />Thanks<br /><br />Ed

 

[rlouns]

Re: Force Top RPM question & a long story

I noticed that you did not mention checking the spark. This is a very important step. I know, I did not check mine because it ran smooth and I could not believe that one cylinder was just along for the ride (but it was). I took a stiff piece of copper wire (approx 12 gauge) and bent a hook on one end so that it would hold on like a spark plug. Then I bent it into a loop so that I could put the other end near the block to see how far the spark would jump. Guess what #1 and #3 were great but #2 was dead. A wire had broken (due to vibration) at the junction block under a plastic cover (90 HP 1991 Force).<br /><br /> Worth a look see.

 

[hndiman]

Re: Force Top RPM question & a long story

Robert,<br /><br /><br />ur right forgot to mention i checked spark and may yet do the force handbook checks, i also changed the coils, (force of habit I have found strange problems with coils over the years). <br /><br />Stay tuned, should have a test with a 15" prop in a day or two...<br /><br />thanks for the input<br /><br />Ed

 

[my new fishmaster]

Re: Force Top RPM question & a long story

I have a 96 17 fishmaster Starcraft boat with a 75hp engine. I started with a 17 pitch and have droped to a 11 pitch now my rpms are around 4900 wot and goes 30mph. I just installed a fuel pump diaphram kit and now can not get the engine to run. I installed like the instructions but did not break off the plastic thingys by wiggling them back and forth. I used a golf tee and drove them home could they be to tight now?

 

[hndiman]

Re: Force Top RPM question & a long story

hi,<br /><br />not sure about the golf tee part, but as long as you had the plactic rivet pushed tight against the housing when you pushed in the expander i would thinks the pump is ok.... but if the engine doesn't run as good as it did before u started the pump rebuild i would think you might have caused it... i have also found that the fuel line need to be tight use tie wraps they are better then clamps

 

[hndiman]

Re: Force Top RPM question & a long story

ho to all that might have followed this...i tried the 15" pitch prop and picked up 1,000 rpm, summary 19" inch to 17" no rpm change, 15" equal a 1,000 rpm gain....go figure