75 HP force lost top end

[curtiss]

My motor has suddenly lost around 1000 rpms. it use to run at 5200rpms and now only 3800 to 4000, so far I have gone through the carbs had some varnish build up on the jets, increased acceleration but no help on top end. We chaecked the stator voltage did not have a dav but used a fluke 85 multimeter and converted rms to peak and peak voltage was 84 should be 100. Is this a valid check? Any other suggestions?

 

[Rex]

Re: 75 HP force lost top end

IT SOUNDS LIKE YOU LOST SOME TIMING.<br />JUST A GUESS BUT THAT WHAT I WOULD CHECK<br />FIRST.

 

[curtiss]

Re: 75 HP force lost top end

Sorry I forgot to mention set timing and checked compression(140 -150 on each)

 

[my new fishmaster]

Re: 75 HP force lost top end

Cap I tried my new boat for the first time today on a local lake. Mine is a 96 75hp force with 25hours. My top speed was only 20mph at 3500 top rpm? It did not have that 2cycle growl at all. I just dumped the mistery gas and have taken the fuel pump apart. I have noticed fuel around the carb and alot on the hose that attached on the bottom of the carb. What does that hose do?

 

[curtiss]

Re: 75 HP force lost top end

I believe it supplies the fuel to the carbs

 

[dmessy]

Re: 75 HP force lost top end

Yo Capt., I'd recheck the timing dynamically in a tank with a test wheel. If it is spot on, look to the fuel system(partially clogged main jet?)<br />My new Fishmaster.,Been watching your saga with your Force, better get a manuel and go step by step. Brass screw on bottom of float bowl allows fuel to go to the choke solinoid for cold starts. Replace that gasket (and rubber hose while you'er at it) and the drool will cease. Your telltale water line(pee hole) should pass h20 shortly after startup regardless of engine temp.Good luck on sorting your problems out. This site is awesome for advice!!

 

[curtiss]

Re: 75 HP force lost top end

Checked timing in lake. Talked to local repair shop today and they told me I could just use a multimeter to check the stator voltage and it should read according to the manual. Is this correct?

 

[dmessy]

Re: 75 HP force lost top end

Yes a multi meter will do. How did you check the timing? With a timing light while running WFO across the water or did you tie up to the dock and make some waves? Did this problem come on suddenly or gradually?

 

[curtiss]

Re: 75 HP force lost top end

Checked timing running across water WFO with a timing light. The best I recall the problem started when I had left a plug wire off and could not get the thing to idle. I tried reving a couple of times thinking it was loaded up when my buddy heard it arcing. Put plug wire back on left the dock and couldn't get abve 4000rpms. Have checked the resitances on the coils and they are good. The only thing we didn't check was the trigger voltage. Have been through carbs. Tehy are clean.

 

[Rex]

Re: 75 HP force lost top end

START FORM WORD GO.<br />IF IT IDLE OK THEN CHECK TO SEE IF YOU LOSSED<br />OR GOT A LOSE HOSE.<br />CHECK YOUR FUEL HOSE TO MAKE SURE IT NOT GETTING AIR.<br />THEN GO TO THE LINKAGE TO MAKE SURE <br />EVERYTING IS MOVING RIGHT.<br />IT SHOULD BE JUST FINDING SOMETHING SMALL.

 

[joeripp]

Re: 75 HP force lost top end

Cap,<br /><br />I have a 70 hp Force motor that had the exact same problem. <br />I pulled the plugs and looked at each one of them and found my number three cyl was not firing. I checked the voltage going to the coils (which was fine) so I cleaned the connections to the coils and the rpms came back up. Haven't had a problem since.<br /><br />Maybe this will work for you.<br /><br />-Joe

 

[clanton]

Re: 75 HP force lost top end

If it is a thunderbolt ignition system (Merc) the stator output on low speed side is 200 volts with peak meter and pack output is 150 volts. Someone on other board said you cant convert because stator output is not true rms. ?????

 

[Don Schmidt]

Re: 75 HP force lost top end

I had a 1985 85 Hp. Force that started losing top end rpm,and it turned out to be almost everything in the electrical system (coil,stator,ign.module,etc.)had failed. I was told by the mechanic that repaired it that unfortunately the ignition system was designed so that once one part starts to fail it takes other parts with it. Not a good design if that's true. Also very costly ($550).

 

[dmessy]

Re: 75 HP force lost top end

Yo Capt.,<br />Running the motor with the plug wire off fried something in the CDI. The manuel has a big note of caution about not even turning the motor over without the plug being in and grounded. Hope I'm wrong but...