Force 120 - No top end

[shawnvv]

Bought a 1990 Bayliner with a 1990 Force 120. The engine fires right up and idles great. When on the water the boat can hardly make it up onto plane. It seems to bog down and vibrate lots. I have great compression on all cylinders (140-160) and spark on all four as well. Just replaced the fuel pump diaphragms. Reeds are good. Checked the timing and its right on. It seems #3 cyl is running a bit rich. How can #3 be rich and not #4? They both run on the same carb. I have a 21 pitch prop.
Suspect....
1-Bad carb
2-bad coil?
3-wrong pitch prop
??

Quick question... Will the over temp sensor make the engine go to limp mode?

Thanks people
Shawn

 

[jerryjerry05]

Welcome.
No limp mode on your motor.
You should have a buzzer under the dash for the overheat.
Ground out the Orange lead on the junction strip.
It should make the buzzer sound off.
If it's idling good then dies, it's possible the high speed jets dirty?
Is the linkage moving the trigger base as you throttle?
Does it do this with the cover removed?

 

[pnwboat]

21 pitch prop is probably too much. You might need a 17 or 19 pitch prop depending on what your WOT RPMs are, and hull design/length.

Water logged floatation foam under the deck can add hundreds of pounds of weight affecting perfromance.

 

[SkiDad]

you checked all the things I would think of - i wonder if you just need to run some cleaner through you engine and maybe something like Mercury Quickleen and or a spray carb cleaner.

 

[shawnvv]

Thanks for the input guys! The linkage is moving the trigger base (advancing timing) and I am going to try and find a lower pitch prop.
The mercury quicleen... is that basically a carb cleaner. I pulled the carbs apart and their spotless. I guess its impossible to see whats jammed in the orfices!
Which is the high speed jet? The one in the centre of the bowl?
Shawn

 

[SkiDad]

you put the mercury quicleen in your gas tank mixture - i used it when I got my boat the 1st year for a month or so and when i did get a chance to test my compression it was 150 per cylinder and I think it probably cleaned up some of the crude. a 17p would really help if your boat is 18' or 19' long.

 

[SkiDad]

this should fit your motor. it will fit either style of lower unit. You will need a aft spacer if you have the closed style of prop currently as the plastic flare won't fit. But if you have the open hub like this one you probably already have what you need. http://www.ebay.com/itm/1989-FORCE-..._Accessories_Gear&hash=item4d21c2d888&vxp=mtr

or look at new ones on this site. if you have a closed style hub with the plastic flare look at Michigan 072107 - it will probably be a better prop if you take that style.

 

[Jiggz]

As mentioned, start with a lower pitch first like 19P instead of a 21P. If problem persists, investigate why #3 is rich and not #4. The only thing I can think of is you might have clogged fuel recirc system between #3 and #4. It could be that unburned fuel from #3 is not draining into #4 which is supposed to be the case. The other thing could be that there is high carbon build up saturating the cylinder resulting in rich mixture and this results usually with the fouling of the spark plugs.

 

[jerryjerry05]

"When on the water the boat can hardly make it up onto plane. It seems to bog down and vibrate lots."

You posted this. Does it get up on plane at all?
What rpm's are you getting?
Take the cover off and see if it runs then.

 

[shawnvv]

jerryjerry05, it does eventually get up on plane if everyone piles into the front. then it runs a little smoother around 3500-4000 rpm. I have the carbs currently soaking in some carb cleaner. One thing I found strange is this little standpipe in the upper carb cocked off to one side in the picture. Would this affect top end? The other one looks normal.

Was the ignition system reliable on these force engines?

Shawn


bottom

 

[jerryjerry05]

Normal on both.
Do both carbs open at the same time?
Does the butterfly at WOT lay flat? or close to flat?
What is the compression reading on each cylinder?
Your motor should be all about the same.
What boat do you have?
Does it stay on the trailer or in the water?
The Bayliners with a 120 came with a 17 or 19p aluminum.
You sure it has spark, good spark on all 4?

 

[shawnvv]

Just put the spotless carbs back on and sync'd the butterfly's. Went for a test run at the lake and no change. Theirs spark on all four plugs when cranking. Compression is about 150 on all four. So now I'm starting to think its ignition. I thought I read the force requires more voltage at higher rpm's???

 

[jerryjerry05]

About 150?
The fuel pump is operated on the compression and low comp could be a reason.
No such thing as needing higher/ more voltage at higher RPM's.
Check for loose connections from the stator and trigger.
I had a wire break inside the shrink wrap on the trigger leads.
Very tiny wire, easy to break.
You check the fuel line and connections.
The connection could be sucking air?
The hose might be collapsing and shutting off the fuel.

 

[shawnvv]

Well lads, buddy of mine lent me a 17 pitch prop and the boat flew onto plane in no time. What a difference!! I bought the boat with the 21 pitch thinking it was standard but its obvious it was too much.
Thanks for all the input. Its great to know you guys have my back when I need help.
Till next time
Shawn

 

[SkiDad]

that's good to hear! What kind of rpm and speed did it take you to ?

 

[shawnvv]

Well lads, buddy of mine lent me a 17 pitch prop and the boat flew onto plane in no time. What a difference!! I bought the boat with the 21 pitch thinking it was standard but its obvious it was too much.
Thanks for all the input. Its great to know you guys have my back when I need help.
Till next time
Shawn

 

[shawnvv]

I reached approx 5000 rpm. Theirs a local prop shop I'm going to try a few other props to see what works the best.
My buddy said the boat originally might have come from the coast at sea level and thats why the prop might have worked. I'm at 380 m or 1250ft. Are .094" jets the right size? Should I try smaller or bigger?
Shawn

 

[SkiDad]

1250 ft is nothing to worry about. don't do any higher than 17p - 5000 is good for almost all uses. if that was a michigan prop and a direct fit I would look at getting the same one or find one on this site that is michigan for your year in 17p. If you are pulling really heavy slalom skiers you could drop to a 15p since you have some room rpm wise but if not I would think 17p is the way to go.

 

[shawnvv]

Ok good to know. I'll try getting up single ski with the 17p.

 

[Jiggz]

Get a stainless 17P if you can for it will perform a tad better than Al.