1985 Force 125 WOT/General

paul88

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Jun 6, 2008
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28
Hello,

I bought an 85 bayliner 19' w/ force 125 last summer and ran it all summer without any problems, and on season two, I'm starting to learn more about this boat and I have a few questions.

It starts great, and every plug jumps a 7/16ths gap at idle speeds. I've replaced the plugs with autolite plugs, referenced from the chilton repair book.

My first problem is whenever I've been running for a little while and turn the engine off to let someone in or out of the water, and then start it again, it dies after 1-2 seconds of running. Turning it over again starts it again, but I have to put it in gear pretty quick or it'll die out. I replaced the priming bulb, and squeezing it when it won't stay running seems to fix the problem. Is this a recirc problem or is there some kind of check valve I can replace? I think it losing gas in the primed line to one.

If I decarb, I can see some exhaust fumes coming out around the engine from somewhere, however, running the engine on the water with the cowl hood off makes no difference. Is this something that I should try to fix or if I see no change in performance with the cowl off, does it matter?

My real problem is my WOT RPM. I have a tach in the dash that reports 4100 RPM at WOT. I have checked that the butterfly valves are completely open on full throttle, adjusted the timing, change the idle mixtures, plugs, all with no result. At 4100 RPM the inboat speedo says 31, GPS says 30.5 or 31.5 (up or down stream) and I have a 17 pitch stainless with cups, and it has some dings and a dull leading edge. I believe that this lower unit is 1.78:1 ? I'm not sure on this, it seems to be stock. According to some prop calculators, that puts me at 22% slip. 30mph is fast enough for my purposes, but I'd rather not have a cylinder freeloading gas into the water. I've heard that the CD could be bad, lacking capacitance to support the high RPM, but I'd rather not pay 180 dollars on a hinch for one of these things. Is there a way to test these without a special high voltage meter or anything? The manual wants me to use some tools I don't have to test it. Swapping them won't do me any good since they're all firing at low rpm, as soon as I throttle down, the plugs will clean up, and fouling doesn't seem to be a problem.

Finally, the last owner put some paint on the hull with a brush. Its some expensive anti-fouling marine paint, but it is very rough, like sandpaper. Is this going to make a significant difference on the water? (More than 3mph (10%))

Thanks for any help!
 

jerryjerry05

Supreme Mariner
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May 7, 2008
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17,923
Re: 1985 Force 125 WOT/General

The very first thing to do is a compression test.Remove and ground all the plugs and push the throttle all the way forward.Jump the selonoid and take the readings.They should be as much as 155#.But could be less depending on your guage.The reading should be within 10-15# of each other.
If your getting good spark your packs aren't bad.
Is 4100rpm at WOT? If so.It sounds like you need to put a smaller pitch prop.That motor should run 5200-5500wot.If you have a 17c Stainless then you need to go to a 15c St or 17c Al.
The bottom shouldn't make much difference.Sand it down if you have time.
Come back with the comp test and tell if that is the rpm at WOT.Jerry
 

pnwboat

Rear Admiral
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Oct 8, 2007
Messages
4,251
Re: 1985 Force 125 WOT/General

I have a 1988 bayliner bowrider with a 125 HP motor. I'm running a 17 pitch non-cupped prop at 5500 RPM and it pushes the boat to 45 MPH. Sounds like the motor is not trimmed out correctly, or it's not putting out full power. Like jerryjerry05 states, need to check compression.

I'm using some NGK BUHX surface gap plugs in mine. They seem to work the best for me. Never tried the Autolite brand. I've not heard of anyone using the Autolites in this particular motor. You can do a "search" on plugs on this forum. I think you'll see what I'm talking about.

If squeezing the primer bulb keeps it going at an idle, it may indicate a fuel supply problem. Have you done anything with the fuel pump? You didn't mention whether or not you inspected/changed the fuel pump diaphram.

If compression checks out might try changing plugs, then fuel pump if you haven't already done so.
 

paul88

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Jun 6, 2008
Messages
28
Re: 1985 Force 125 WOT/General

Ok, thanks for these suggestions.

I just got back from the river with a new alum 13.5xR15 and it would run 4750 WOT with 4 of us at about 31mph, and 5000 WOT with just me in the boat at 33mph. The old stainless 17c would get 4100 WOT at about 31mph. I need to invest in a compression checker, and I will check compression tomorrow. These plugs are brand new autolite surface gap plugs that cross referenced from those BUHX.

As far as trim, the unit needs a check valve replaced because it leaks down when it shifts to the high rise cylinders. I've seen the part number somewhere here before, but its a $4 part with $12 shipping, and I can't justify that much shipping for something the size of a golf tee. The smaller shorter throw trim piston doesn't leak as much, so I just tolerate it. I try all trims to find the best one for highest RPM without ventilation. I'm a new boater, but to me this means trimming so that the motor looks level, but I play with the trim to be sure.

At about 1800-2500 rpm it seems to miss some. The engine jerks a little and you can feel a random, bouncy change in thrust. The timing lock nut was missing so I just set it between the suggested 1/2 to 3/8ths inch range, and I need to get a new nut to put on it before I time it accurately. I have the procedure to do this, and a timing light. (Full throttle, grounded plugs, 28 deg according to the book at cranking speed). My experience with changing this timing is no more than 50rpm change.

As far as fuel, the only maintenance I've done is checked the screen for any trash, and I put some seafoam in last tank. The previous owner had a water separator installed, which looks pretty new along with the gas tank itself. The vent works well (it blows pretty good with the gas nozzle in fill-up). I haven't changed the fuel pump or any fuel parts. I'm running 87 octane with 50:1 ratio, and I've tried 91 without any change. The faded sticker says 83 or better.

The engine idles well on a cold start, but if I let it sit for 5-10 minutes then try again, it needs re-priming. Alternatively, using the choke switch gets it going. If I start it within a minute of turning it off, it starts just fine. Water flow is fine, and you can touch the engine after it has been running, though not hold your hand on it for more than a few seconds.

The only fuel setting I've changed is the idle mixture screw and its about 7/8ths of a turn out, though I haven't properly set it because I wanted to get the idle RPM down some first, but the lowest idle setting that the cam and linkage will allow is 850rpm in forward gear, and the book says to shoot for 750, so I'll properly set them next time I'm on the water. I will look in the manual for fuel pump maintenance and see if the diaphragm is in good condition.

This engine lacks full power, and I've always attributed that to the 23 year age of the motor.
 

jerryjerry05

Supreme Mariner
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May 7, 2008
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17,923
Re: 1985 Force 125 WOT/General

My motors (twin-85s) both perform the same as when they were new.Do the comp test and get back.Jerry
 

paul88

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Jun 6, 2008
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Re: 1985 Force 125 WOT/General

Compression:
1-148 , 2-148 , 3-145 , 4-145
 

pnwboat

Rear Admiral
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Oct 8, 2007
Messages
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Re: 1985 Force 125 WOT/General

Those compression numbers would indicate that the rings are in very good shape. I would try the fuel pump diaphram next. One other thing. There is a small hole in the by-pass cover under the fuel pump assy. Make sure it's not plugged with carbon. It needs to be clear in order for the pump to work properly.

Also need to verify all the plugs are firing correctly. Have you looked at the plugs closely after a run on the water? Do they all look the same as far as carbon build up? If you have one that is clean, it may indicate that it is not firing correctly.
 

paul88

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Re: 1985 Force 125 WOT/General

There is a small hole in the by-pass cover under the fuel pump assy.
Does that mean its visible without taking any parts off? Or do I need to take the assembly apart to see it?

There is a sierra kit on iboats for $15 or so with a couple gaskets and a diaphragm. Is this what you would recommend?

All the plugs look the same, and a tester shows all jumping 7/16ths gap.
 

paul88

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Jun 6, 2008
Messages
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Re: 1985 Force 125 WOT/General

I just got back from the lake with new NGK BUHX plugs. It missed some at first and then ran ok, same performance as autolites. Squeezing the priming bulb had no effect on WOT. Fuel pump rebuild kit is in the mail.
 

pnwboat

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Re: 1985 Force 125 WOT/General

The hole in the by-pass cover is readily visible once you remove the Fuel pump. It matches up with a hole in the bottom of the fuel pump. There is a gasket that seals the hole in the pump with the one in the by-pass cover.

I was just thinking....I read a post where someone installed a brand new water seperator and caused a decrease in performance. The Fuel pump in the Force motor wasn't strong enough to pull the fuel through the water seperator. Might be worthwhile to bypass the fuel/water seperator by taking the filter element out and running it as a test. Or at least take it apart and look at the filter to see if it is clogged.

You mentioned something about the timing.....Did you ever get that set correctly? If the timing was off, that will really affect the performance. Timing on these two strokes is critical. Too much and you can melt a piston. Not enough, they don't run to their full potential.
 

paul88

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Jun 6, 2008
Messages
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Re: 1985 Force 125 WOT/General

Well I installed a new diaphragm and gasket today. All the holes I could see I sprayed with cleaner. The whole assembly had been painted white by a previous owner, so I'm not sure if this clogged any pinholes or not, but I couldn't find anything covered up. The old diaphragm looked stretched. Also, should there be hose clamps on every hose to the assembly or only the gas lines? Where would I get the gasket that goes with the screen on the gas-in side? It wasn't in the rebuild kit.

I timed the engine correctly, but lost the locknut, so I'll be doing that again. It only resulted in marginal performance gains, as it was pretty close to begin with. I'll run it once with the separator and see the results, and then I'll test again without the separator. Thanks for the tip.
 

paul88

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Jun 6, 2008
Messages
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Re: 1985 Force 125 WOT/General

I just got back from the water again. 5000RPM WOT Max with a R15 at about 30mph. I timed it properly, new plugs, resynced carbs, adjusted linages, and rebuild fuel pump. Any more ideas?
 
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