The FORCE has left me and i need help.

[muglydog]

I bought a 1990 Spectrum with a 120 h.p. Force,(same age) The gentleman I bought if from had a heart attack and the boat had not seen the water for over a year. It had not been registered so I did not get a in the water demo. It did start easily using the hose and ear muffs and idled fairly smoothly. <br />Just for grins when I got it home, I bought a repair manual, replaced the lower unit oil, waterpump impeller, Thermostat, all fuel hoses, fuel filter and installed a new fuel pump diaphragm, and spark plugs, boiled out the carburators with new gaskets. I took the boat to the water and it runs smooth but will not go over 3000 revs. I checked timeing WOT and it is IAW the book and the timeing mark is rock solid. Looking down the barrel of the timing light connected to one cylinder at a time the light is of equal brilliance on all four. I have two props, Went to the prop shop and the man said I should be getting at least 4000 revs on one and 400 more with the other, I get the same on either prop. I am getting a lot of experience with the Force but not a lot of satisfaction.<br />My question is WHAT DO I DO NEXT

 

[Trent]

Re: The FORCE has left me and i need help.

Just off the top of my head..<br /><br />Are the carb butterflys opening all the way?<br /><br />And did you just replace the fuel pump diaphram or did you replace the check valves too? And is the fuel bulb staying hard when its acting up?

 

[12Footer]

Re: The FORCE has left me and i need help.

It sounds like you did all the right things so far. If the engine isn't surging, I would suspect the tach is inacurate (multi-pole,with one pole missing pulse) or throttle plate WOT posistion as Trent sugested.<br />But beetz me. Strange.<br />Had to edit, just thot of something. Do a comression test. Then a good spray- type decarb treatment,then check compression again. On a stored engine, the rings can sometimes stick as if they were welded to the piston.

 

[sony2001]

Re: The FORCE has left me and i need help.

Most likely a FORCE running at 3000 rpm's is a FORCE on 3 of the 4 cylinders. Can you run your timing light when on the water? I bet a bad CD unit.

 

[trevorcday]

Re: The FORCE has left me and i need help.

Most Forces running at 3000 RPM are 4 cylinders running on 2.5 cylinders because two cylinders have broken rings. Do the compression test or just cover the plug hole with your thumb and turn over the motor (with your other hand). If any cylinders have low compression take off the head. The CD box would be a more favourable condition but i am afraid less likely.

 

[muglydog]

Re: The FORCE has left me and i need help.

Thanks for the advice. It has helped but not yet solved the problem. If I wasn't such a tightwad or afraid of getting ripped off by the local wrench's, the motor would probably be running by now, and I would not get the training and skills I am acquiring. Glad I'm taking the long route. It will pay off in the end, I'm sure. <br /><br />To answer Trent: yes all butterflys are open. I did a carb/timing syncronizing according to the book. I did not change the check valves in the fuel pump and I do not know if the bulb is staying hard. Is it supposed to? <br /><br />12footer: by the way I have read many of your posts and have learned to respect your advice. I bought a new tachometer and it is the one that reads 3K at WOT. Compression is 130 to 140 between high and low. I did a spray de-carb and left the motor set for several days to soak. compression did come up. I am now running an additive in the gas which is supposed to de-carb. <br /><br />MrMerc: I can run a timing light on the water. I did and changed the lead from cyl 1 thru 4 while watching the light for changes in brilliance between cyls. There was none. <br /><br />Sony2001: is ther any way to bench test a CD to isolate a malfunctioning one? They cost a lot of buckz just for troubleshooting. <br /><br />If the high speed jets are for high altitude, could they cause this problem? I operate at 1200ft?

 

[trevorcday]

Re: The FORCE has left me and i need help.

Is the compression ok on all cylinders?

 

[rogerwa]

Re: The FORCE has left me and i need help.

Just for curiosity.. What tach did you put in? I understand that the Force motor requires a 20 pole tach. Is it possible that you are just getting errant readings?<br /><br />Can you check your speed on a GPS? <br /><br />Just a thought..

 

[muglydog]

Re: The FORCE has left me and i need help.

for Mrmerc: the compression is a little low, the book spec is 140-160. I get 130, 138, 130 and 140 dry and 140, 150, 140 and 150 wet<br /><br />Wit a GPS my speed is 19.2 knots. My boat is a 24 ft Spectrum which is a called a tunnel hull aluminum boat which is a like a pontoon/deck boat .

 

[muglydog]

Re: The FORCE has left me and i need help.

Oops, didn't answer rogerwa. <br />The tachometer I installed is a teleflex and according to the sheet it is for "force outboards with 20 pole alternator". I have had friends come onboard and they do not feel that "judging from the sound", the motor is not running at full rpm. I wish i had access to a master tachometer to check it out though.

 

[sony2001]

Re: The FORCE has left me and i need help.

At 3000rpm the 4 cylinders are firing. Then change the carb jets to sea level size. Probably .092 inches. Use the prop that should give 400 rpm's more than the other. Drain the carb bowls there could be water trapped there. Look for a used CD they are good to have around.

 

[trevorcday]

Re: The FORCE has left me and i need help.

Sorry for being such a sceptic about the compression but blown up powerheads seem to be the most common cause of the type of problem you describe with Forces.<br /><br />Here's a thought. Try making index marks on the flywheel so that you have a TDC mark for all four cylinders then check the ignition timing on each cylinder individually. With the merc CD ignition each spark is triggered separately and a bad trigger assembly can cause the ignition timing to go out of wack on one cylinder independant of the rest. It's rare but it can happen. We had a 3 cylinder that first blew up the #2 piston and then (after replacing the powerhead) ran backwards for this very reason. Just a thought.<br /><br />I am not aware of a bench test for the CD unit but by following the diagnostic procedure in the manual you can quickly determine which ignition component is faulty. Usually bad CD unit (power pack) = no spark on one cylinder.

 

[Trent]

Re: The FORCE has left me and i need help.

Maybe this site will help some?? <br /> http://www.homestead.com/dolphinmarineservice/ign2.html

 

[rloper]

Re: The FORCE has left me and i need help.

Muglydog, If that boat is a 24 foot type pontoon boat it might be that you are over proped. The 120 Force is not rated at the foot, it is rated at the head. That is a lot of water to push. What is the pitch of the prop?

 

[muglydog]

Re: The FORCE has left me and i need help.

The first prop is a 13.75" X 15 pitch, 4 blade. <br />The second is 12 5/8" X 21 pitch, three blade.

 

[Rex]

Re: The FORCE has left me and i need help.

I agree overprop. You can not except 400 RPM<br />on a 21'. Check to see if anybody got<br />a smaller pitch like a 10 just to see how she<br />does. Watch the tech.<br />Good luck

 

[sony2001]

Re: The FORCE has left me and i need help.

You won't find a prop smaller than a 15".<br />On the 120-125 hp its used on boats in the 20 to 25 foot category. Why didn't you tell us its a pontoon craft at the beginning?

 

[johnkc]

Re: The FORCE has left me and i need help.

we used to get a 11 pitch for our 24ft spectrum pontoons with90 hp force ,iwill have to check on this prop on 12/19/01, i will let you know what i find . is this pontoon of the catermaran style or the regular round tubes?

 

[DJ]

Re: The FORCE has left me and i need help.

muglydog,<br /><br />You're overpropped. I agree with loper. Every inch in pitch on a prop is good for about 200 to 300 rpm change. I believe you can find smaller than a 15". Mercury Marine offers a great number of props-for Force also. Newer Force engines have Merc. lower units.<br /><br />Double hull boats are power eaters. 2-Stroke engines do not handle "lugging" well. Change that prop.

 

[muglydog]

Re: The FORCE has left me and i need help.

For sony2001: Sorry about the oversight on the hull style, but I did define it as a Spectrum 24 in my first post. After many years in sailboats this is my first power boat and I did not realize how important it would be. <br /><br />For all: Thanks for all the info. After the holidays I will get back on the problem. I have asked Michigan Wheel for a prop reccomendation and will comply with their suggestion. meanwhile I will try to find a 10" loaner.<br /><br />meanwhile I will try the other suggestions and let you know what works.<br />1. clean/Replace fuel pump check valves.<br />2. More decarb treatments<br />3. Make index marks on flywheel for each cylinder and check each at WOT.<br />4. check jets and drill out if required.