1988 Force 85hp Top end rpm loss troubleshooting help.

[DunbarLtd]

You can try: drop the lower unit, remove the thermostat, hook up something to block off the extra room at the thermo
hole, and try to blast the water out of the motor.
Turning on full pressure and try to backflush and maybe more pieces(if any) will come out?
That can also loosen the pieces(if any) and cause a new block??

If a part's caught? then the next step is remove the head and check for pieces there?
Some motors have plastic/rubber pieces in the block used to act as diverters for the water, don't remove.

OK Ill have a go at it. I blew out the pressure gauge hose and checked the pressure again with a spare tire. So now I know for sure the gauge is not the issue. I will have to drop the LU again and see if i can find any pieces clogging it up. Thanks for the tips.

 

[Zink357]

Seems like 32mph out of that motor is pretty good, but could be better. I would seriously try a different prop, but maybe the tach isn't accurate? What kind of fuel are you using? Have you checked your speed by GPS or are you relying on the speedo? Try using GPS if you haven't. I agree you should get higher RPMs out of it but I always question the old gauges. Mine shows that I'm getting 6500+ RPMs out of my 125hp Force and it doesn't seem to me like it is over reved at all.

 

[DunbarLtd]

Seems like 32mph out of that motor is pretty good, but could be better. I would seriously try a different prop, but maybe the tach isn't accurate? What kind of fuel are you using? Have you checked your speed by GPS or are you relying on the speedo? Try using GPS if you haven't. I agree you should get higher RPMs out of it but I always question the old gauges. Mine shows that I'm getting 6500+ RPMs out of my 125hp Force and it doesn't seem to me like it is over reved at all.

It doesnt sound like mine is over revving either. It sounds like it can spin faster and the tach proves that. Its a gauge specific for these forces (20 pole) not the universal ones so im sure its accurate but i have no way to prove that. It shows 750rpm is gear and it sounds like its 750...so im guessing its accurate. It doesnt have any idle issues. it will idle fine all day other than loading up the plugs. But if i run it hard and clear it out itll idle fine again. Dont really have a hard time restarting it.

I use gps and with two different sources they were within 1-2mph so gps works fine. I took old speedo out and put in the tach.

As an update to my issue i removed the head to inspect the water jackets and they were clear. It had the original head gasket still on it. I know this because theres still the original block blue paint on the gasket from when it was factory painted. I cant believe its never been changed. Unless someone painted the head last time it was changed but i doubt that happened.

I found a couple bolts completely rust covered. And 2 or 3 that the threads were oily. Luckily didnt snap any.

Seems like it was leaking to me. Whether it was actually leaking water in or oil out i dont know. The gasket wasnt torn. Perhaps it was on its way out sooner than later???

Ill be interested to see the compression after i put the new one on. If it doesnt fix it then thats fine. Bound to need one at some point anyways.

So thats where im at with it at this point. Will update when i get it out on the water next week or so after the parts come in.

 

[jerryjerry05]

Tiny Tach great little item you can just wrap the lead around a plug wire and see the rpm's
I bought one 3-4 years ago. $16

In fresh water, the head gasket should last a very long time.
Salt water it's a different story.
Forces weren't made for use in salt water.

The salt condenses in tight spots and slowly eats the steel in the sealing ring
of the gasket.

 

[DunbarLtd]

Hey I have a quick question about the tach. I found a multi meter at harbor freight that says it reads RPMs. I was wondering if anyone has any experience with these on outboards? It comes with the coil wire attachment. Im thinking of using it to compare to the dash tach i just installed. Really trying to rule some things out here.

Also about the head gasket that just showed up in the mail. I was going to add some aviation gasket maker from permatex to the paper part of the gasket not the metal ring that seals around the pistons. Just wondering if that would affect these gaskets. I bought a oem Mercury marine gasket off bid site.

 

[jerryjerry05]

You don't need to add anything to the gasket.
The only way I'd add anything is if the head or block wasn't as smooth or straight.
Then a small amount in the bad places.
I have had to use it only 1 time in a long time.

The meter, ask them about their return policy??
The tech on some of their stuff is seriously lacking.

 

[DunbarLtd]

You don't need to add anything to the gasket.
The only way I'd add anything is if the head or block wasn't as smooth or straight.
Then a small amount in the bad places.
I have had to use it only 1 time in a long time.

The meter, ask them about their return policy??
The tech on some of their stuff is seriously lacking.

Dropped the LU again and ran full pressure hose through tstat opening. Very small black particles came out but nothing that looked concerning. Water ran out from the leg pretty good.

The small opening in the very bottom of the exhaust tube connects to the passage where the water tube is??? I can see the water tube from that small square hole, looking from exhaust passage side. Whats the purpose of that small hole???

Also the water tube seal was leaking exhaust oil...I dont know whats going on there.

Other than that i am gonna assume the water pump is working correctly and there isnt a block in the system.

I have a temp laser gun now so ill check some temps when running and post back here.

Also im pretty sure exhaust gases (evidence of oil) were leaking out from where the LU contacts the midleg. I was going to add a little sealant along that seam. Im assuming this is unnecessary though???

 

[jerryjerry05]

????? Pics?

The small opening in the very bottom of the exhaust tube connects to the passage where the water tube is??? I can see the water tube from that small square hole, looking from exhaust passage side. Whats the purpose of that small hole??? Also the water tube seal was leaking exhaust oil...Pics?

You seal the lower unit and the unburned fuel and oil has no place to go.
No sealer.​

 

[DunbarLtd]

Is this hole where the water exits after pumping through the powerhead? Thats the water tube inlet you see through the small hole, looking through the exhaust "tube". And since this hole connects to the same "chamber" as the water tube is in, unburnt oil leaks down and through the rubber grommet that keeps the water tube in place.

Im curious if oil leaking past that seal makes a difference? I guess it would just drip down onto the top of the water pump and not cause a problem???

I apologize if these are stupid questions but again i have to remind everyone i am a complete newb to these motors so i hope you can excuse my ignorance. Thank you.

And I was wondering if you seal the surfaces where the lower unit and mid leg meet? I didnt see any oil dripping down the outside of the lower unit so i guess i have to assume it wasnt leaking past the mating surfaces??? I just noticed oil along the edges, which is visible in this pic. And that oil there is unburnt oil and fuel. Same for the rubber grommet. I confirmed i do not have gear oil leaks or power head leaks.

 

[jerryjerry05]

Is this hole where the water exits after pumping through the powerhead? Yes.

If there is a leak from the water tube grommet, then a gasket or seal under the powerhead gone bad.
Yours looks normal.
It needs no sealer on the cases.
The excess oil/gas leaks down and finds a way out.
The front of the drive should have 2 small holes for water to drain.
Make sure they are open.​

 

[DunbarLtd]

Is this hole where the water exits after pumping through the powerhead? Yes.

If there is a leak from the water tube grommet, then a gasket or seal under the powerhead gone bad.
Yours looks normal.
It needs no sealer on the cases.
The excess oil/gas leaks down and finds a way out.
The front of the drive should have 2 small holes for water to drain.
Make sure they are open.​

OK thanks.

 

[DunbarLtd]

I took it out yesterday. Kinda windy but not too bad in the morning. I dont know what the compreession is but i kepy an eye on the head and never saw any water leaking.

Still only seeing about 6-7psi at full throttle. But the exuast idle ports were spraying pretty darn good at idle. I have to assume its getting good water flow. I just could have sworn the psi was greater when i first got the boat.

Anyways after a couple mile run i grabbed the laser thermometer and like you said the hottest part of the head was near the plugs. The hottest spot i could find was almost 130F and that was at the very bottom of the power head just where the exhaust tube begins. I dont know how much water us thrown into the very top part of the exhaust tube but that tube seems to have been pretty hot. The rest of the head was maxed out about 110. So it looks like its cooling.

If that base gasket has failed is it possible water is not flowing into the exhaust chamber and therefore not cooling the exhaust tube enough or should i not worry about those temps there?

Again I had an issue with top speed and topped out at 30. Well when I got home I removed the carby shroud and looked into the throats after i put the helm control in full throttle and noticed the plates werent all the way open. So that may be part of the problem. I have re synced them and made 100% sure they are set right. I also adjusted the cam on the roller. I will keep the shroud off next time to double check the plates while on water.

If I changed the exhaust gasket, head gasket, impellae, adjusted the linkages. And I still have good compression and its not a fuel related issue then I guess i can try a different prop.

Thanks for all the help. Looks like there isnt much else i can do about this issue really.

 

[jerryjerry05]

Next trip: run with the cover off and manually advance the throttle cam and see if that helps?
The butterfly's don't have to be perfectly level to achieve wot.
As long as they start to move at the same time they should be ok.

Do the starting fluid test..
Spray SF around the intake side and see if that makes any difference??

I never really trusted a water pressure gauge on an outboard??
It sound like yours is pumping plenty of water.

The temps sound great.
Don't worry about the temps once the water leaves the block.

 

[Jiggz]

Just out of curiosity, where is the timing set at?

 

[DunbarLtd]

Just out of curiosity, where is the timing set at?

Can I do the timing while the motor is running on the water or do i only do it on muffs or bucket and cranking the engine?

I keep forgetting to do it actually. I guess i assumed what people were saying in that if the flywheel hasnt been messed with and it starts and runs ok then the timing is most likely ok. But who knows maybe its off a few degrees???

I have checked for top dead center and it lines up with the "zero" mark. I know that doesnt necessarily mean its correct @ WOT but just thought Id throw that out there.

But I do have a light and do need to check it. I just havent gotten around to it yet. Kinda wanted to rule out al the other things first that needed attention and i feel like ive done most of those things. So checking timing makes sense.

I suppose i could do it in the garage on muffs and just crank it for a few seconds? I have been looking for a large bucket to fit the leg into but cant seem to find anything. I have a large trash can but it still wont fit. I need like a large plastic tub. Just havent found one yet.

Any tips on how to do the procedure would be great thanks?

And I believe the service manual says 28 degrees at "cranking " speed. Which is somewhat confusing to me. Does that mean only when you crank the engine over with the key or when the engine is running @ idle?

 

[Nordin]

You can set the timing to 28dgr BTDC at #1 plug with the throttle at WOT and at cranking speed, no idle just crank with the starter motor and throttle at WOT.
This will end up with 30dgr BTDC when running in water at WOT.

 

[Jiggz]

There's a youtube video on how to do this. Highly recommend you view it first. But this is the takeaway.

-Most importantly the engine or motor should not fire while cranking it over. You can do this by pulling all plug wires and fabricating something to ground them so as not to damage the CD modules.

-With the throttle control handle in WOT position, you will need to jumper the neutral switch to allow you to crank it over.

-It's a two man operation unless you have a remote starter

-Note the markings on the flywheel. Usually, there are four markings, TDC and then to the left are three markings with the middle being 30 and to the right of that is the 28 and the other is 32 degree markings.

 

[DunbarLtd]

There's a youtube video on how to do this. Highly recommend you view it first. But this is the takeaway.

-Most importantly the engine or motor should not fire while cranking it over. You can do this by pulling all plug wires and fabricating something to ground them so as not to damage the CD modules.

-With the throttle control handle in WOT position, you will need to jumper the neutral switch to allow you to crank it over.

-It's a two man operation unless you have a remote starter

-Note the markings on the flywheel. Usually, there are four markings, TDC and then to the left are three markings with the middle being 30 and to the right of that is the 28 and the other is 32 degree markings.

Ok sounds easy enough. Thanks for the help.

 

[dadofemily]

I'm pretty sure you are over propped. You said this is a new prop. What was the old one and what RPM did it do. For comparison, my 16 ft bayliner with a 75hp runs a 10 inch diameter 12p 4 blade and hits 5100 RPM. I tried a 14P and could only get 4200 RPM. 13 inch diameter and 17P sounds like way too much prop.

 

[jerryjerry05]

The 1988 85 came with either a 13x 17p or a 19p depending on the boat.
If it was a pontoon?? his pitch would have been a 13 or 15p
Even though it's only 10hp different it's a way different setup.