1988 Force 85hp Top end rpm loss troubleshooting help.

[DunbarLtd]

Hey everyone, I started a thread before but it got way too long so I wanted to start a new one with some updated and more accurate findings.

Compression:
#1 cyl - 130 (top)
#2 cyl - 130 (middle)
#3 cyl - 135 (bottom)

I am having issues with top end rpms and would like to know how to troubleshoot this problem. I am not sure where to start.

Ive recently installed a tach and have the idle set to 750rpms in gear.

At full throttle or "WOT", the rpm will max out @ 4100rpm. It has decent start up and idlle/acceleration and does not jump around as far as rpms. Runs steady and smooth at that 4k rpm range.

I was told the rpm should hit 5K or more.

I bought a new prop. 13.25" x 17 pitch on a 17ft Bayliner Capri fiberglass hull.

Replaced all fuel lines. Added inline fuel filter. Rebuilt and adjusted carbs (2x now). Rebuilt fuel pump but did not change out the valves. Just the diaphragm.

In what order should I start troubleshooting? I am not familiar with 2 stroke outboards but have a lot of experience turning wrenches on cars over the last 20 years. Thanks in advance for any help!

 

[foodfisher]

Link and sync post at the top of the forum page

 

[DunbarLtd]

Link and sync post at the top of the forum page

Ive done link and sync many times on this motor. Even tried pushing on the throttle cam when on the lake @ WOT. Did nothing. Actually replaced both cables as well along with steering cable. Both were old and sticky when i first ran the boat on the water so that was the first thing i replaced.

Throttle cable and gear shift cable are hooked up correctly. Carb secondary plates open fully when trigger is fully advanced and throttle is pushed all the way forward. Trigger assembly moves freely, no sticking.

There is no play in the throttle linkages.

I took the exhaust plate cover off last night (to replace leaky gasket after noticing water coming out a bolt) and added some pictures i took.

Not sure if anything looks abnormal that would cause issues. Hoping to get someones 2 cents on this.

Also curious if there was water leaking into the exhaust chamber what problems would arise other than obvious cooling issues???

 

[jerryjerry05]

I don't see anything in the exhaust(before the cleaning) that would cause a problem.

You sure the new prop's a 17p??

What kind of load?
1 person, Coast Guard equipment, 1/2 tank of fuel.
Go for a ride.

You have T@T ??? no, that can make the boat plow and not get up to speed, and if the motors too
low it can make the motor plow.
Tilt lock pin in the wrong hole?

You have whale tail? (yes, that can knock off the speed at the upper end, yet it helps get up on plane)

 

[DunbarLtd]

I don't see anything in the exhaust(before the cleaning) that would cause a problem.

You sure the new prop's a 17p??

What kind of load?
1 person, Coast Guard equipment, 1/2 tank of fuel.
Go for a ride.

You have T@T ??? no, that can make the boat plow and not get up to speed, and if the motors too
low it can make the motor plow.
Tilt lock pin in the wrong hole?

You have whale tail? (yes, that can knock off the speed at the upper end, yet it helps get up on plane)

Firstly, I removed both boxes and two way seats and installed fold up seats so im sure i lost a lot of weight just by doing that. Ive checked the foam with a moisture meter and it did not move the meter at all. This is as far back as i could test until i hit the gas tank. I stabbed the meter all the way down to the hull and it didnt show any signs of moisture. Im assuming it isnt waterlogged.

Load as follows:

I have 2 group 27 batteries for trolling motor in port side stern compartment. Bow mounted trolling motor 45 lb thrust minn kota edge. And pretty heavy tool bag(30-40lbs maybe?) in the center of the bow. After that usually just myself and one passenger and some fishing rods. Couple of tackle boxes that dont weight much. And an anchor (5lb i think) I store up under a lid on the bow..

.Maybe I have too much weight on the bow?

Even if I do, it still doesnt explain the intermittent speed issue. With nothing changed itll go from 30mph on one run to 32.5mph on the next for no rhyme or reason. Ive repeated this on very calm days so weather doesnt matter in this scenario although i do know weather has an effect. But it doesnt matter wind or no wind, same thing. My lake doesnt have current so up or down stream doesn't make a difference either.

Yes the new prop is marked.

Trim and tilt work and I can see improvement when messing with it. I believe I found the sweet spot. Just below where it starts to ventilate. Maxes out 42k rpms. No matter what I try.

No whale tail. Tried it and it didnt help much so took it off. Id rather have top end than quick plane. I dont use the boat for skiing or anything like that. Just a fisherman trying to get his pole bent...

 

[jerryjerry05]

Prop stainless?
A stainless 17p is equal to an alum 19p

Maybe drop to a 15p

 

[DunbarLtd]

Prop stainless?
A stainless 17p is equal to an alum 19p

Maybe drop to a 15p

sounds like you are convinced I dont have engine issues? I still feel like the motor doesnt run right. Maybe I can test some things to make sure? I just dont think any of the things anyone has mentioned addresses the intermittent issue I have when it comes to speed.

If its a prop issue, then I would have consistent issues.

Im sure when the speed goes up and down intermittently, the rpms change but since its only a couple miles an hour of a difference and an analog gauge i cant exactly see the difference in rpms. But I can clearly notice the speed difference on my gps.

But I also feel like if the motor accelerates and runs smoothly then there isnt a problem there. Its all too confusing and nothing makes sense.

 

[jerryjerry05]

If your getting 30mph it sounds like it's running right?????
But try this: get 3 inline spark testers and go for a ride.
See if your dropping spark as you run it??

Does it make a difference if you run with the cover on or off??
Try it and see?? Maybe the exhaust rubber's leaking?
Or the base gasket or the sillycone seals compromised?

Backfiring, coughing or stumbling?

Run the motor and spray starting fluid around the intake side of the motor.
Carb bases and intake port covers and any where you can spray.
Any difference in the way it runs? then it's sucking air?

All 3 carbs opening at the same time

 

[DunbarLtd]

If your getting 30mph it sounds like it's running right?????
But try this: get 3 inline spark testers and go for a ride.
See if your dropping spark as you run it??

Does it make a difference if you run with the cover on or off??
Try it and see?? Maybe the exhaust rubber's leaking?
Or the base gasket or the sillycone seals compromised?

Backfiring, coughing or stumbling?

Run the motor and spray starting fluid around the intake side of the motor.
Carb bases and intake port covers and any where you can spray.
Any difference in the way it runs? then it's sucking air?

All 3 carbs opening at the same time

It coughs only when starting...sometimes. Completely random as well. Most times fires right up after running. Then itll cough here and there. But after it coughs it starts no problem. And thats with no choke. Not sure what that means though???

The adapter plate gasket on the bottom side of the power head is showing signs of leaking but very minimal. Just a tiny bit of wetness around a few edges. Its not even dripping, just seepage i guess. But Im sure its on its way out. Which is a big job Im trying to avoid.

Maybe exhaust fumes are getting into the cowling and smothering the motor at high speed??? Ill run with the cover off to scratch that off the list.

I doubt the exhaust port cover gaskets I replaced will make a difference but ill make sure they arent leaking anymore.

I will do all the simple things first you have suggested and come back with my findings. Im planning on running it tomorrow .

 

[foodfisher]

Coughing/backfiring could/will do damage to the fuel pump diaphram.

 

[DunbarLtd]

I took it out today. Everything seemed good at startup. Ran it for a while and was able to get it to 32.5mph pretty much every run. I feel like it gained about 100rpms. WOT was around 4300k if the gauge is accurate. Still too low but better....

So Im pretty sure replacing the exhaust cover gasket had something to do with it. That is the only thing that i changed.

Took the cowling off while running and it didnt change anything. Ran the same.

I pushed in the choke at full power and it wanted to die so thats good. The inline clear fuel filter is staying full and no air bubbles so i think I can check that off the list.

I still need to figure out how to test the spark while running. Gonna need to bring my buddy out for that one so he can drive.


What I also noticed..... I am only running 9-10psi of water pressure when cruising. My next project is going to be the water pump. But Im curious what an acceptable psi would be??? Doesnt say in the manual....


Lastly, I definitely have a failing adapter plate gasket. Im getting black exhaust oil seeping out from the top side of the plate right under the exhaust cover, so its the gasket. I think the bottom side of the adapter plate is just RTV??? Looks like it in the service manual.

Im not seeing any leakage anywhere else. I tried the rtv trick and it didnt seal it up. Unless I didnt use the right type of sealant??? What would you use? Has to be gasoline resistant id assume...

How difficult of a job is it to replace the gasket???

Any tips on pulling the power head just so i can get at the gasket????

And thanks foodfisher for the heads up...Any idea how to prevent coughing when starting? Ill also take a look at the fuel pump and check that diaphragm, even though i replaced it a couple months back. But seems like a good idea to check it anyways....Thanks again

 

[jerryjerry05]

Pulling the powerhead
Big job.
A small leak(sounds like this is what you have) is something I wouldn't really worry about.
Couple of hints: remove the air intake plenum under the bottom carb, there's a nut in the center of the
mid section just under the adaptor plate on the rear, remove all the covers/cowl, loosen the bottom cowl.
I used an L bracket screwed into one of the top screw holes on the flywheel(1/4-20) unless you can get a lift tool.
Not many places to pry so be careful not t damage the mating surface.

Water pressure, the manual doesn't have specs as they never installed a gauge..
9-10 is probably good.

 

[DunbarLtd]

Pulling the powerhead
Big job.
A small leak(sounds like this is what you have) is something I wouldn't really worry about.
Couple of hints: remove the air intake plenum under the bottom carb, there's a nut in the center of the
mid section just under the adaptor plate on the rear, remove all the covers/cowl, loosen the bottom cowl.
I used an L bracket screwed into one of the top screw holes on the flywheel(1/4-20) unless you can get a lift tool.
Not many places to pry so be careful not t damage the mating surface.

Water pressure, the manual doesn't have specs as they never installed a gauge..
9-10 is probably good.

Well I had a chance to go out today. I put more rtv along the base gasket and it seems to be sealing ok for now.

I replaced the impeller before going out. Bought a full kit with new housing, plate, gasket, water tube adapter. Aluminum housing on motor leg looked ok. No major pitting. Torqued bolts of housing to 70in lbs like it says in manual. Can they be too tight and ruin the impeller???

So when I had it out and running I noticed a few things.

1: Water pressure at running speed(32mph) was around 6psi. So im losing flow somehow.

2. I put it in fast idle and the pressure would climb around 10, but at times it seemed intermittent. I assume this is because the motor was cold after shutting down and the thermostat hadnt opened yet. Or theres an obstruction somewhere in the system.

3. I tried running without the thermostat and the pressure dropped to 3psi or so at cruising speed. I guess that makes sense. Overheat buzzer never went off though.

4. I also took the water pressure hose off and ran full speed and it looks like water was shooting straight up and out of the barbed fitting (aka tell tale). I dont know how much is normal though. But it looked like it had decent flow.

5. I noticed the bottom cylinder was pretty hot to the touch. The other cylinders didnt feel as hot. And the exhaust tube right below the head where it bolts to the adapter was really hot. Too hot to hold my hand on it. I checked this as soon as i stopped after a long run, motor still running.

Is it likely the water jacket in the head is clogged? Or is it more than likely an impeller installation issue?

Any tips on how i might do some tests so i can figure out what i did wrong? I thought about pulling the head to see if its clogged but id like to rule some other things out first.

When I got home, I took the water pressure hose off the top of the power head and put a gauge on it and hooked it up to a spare tire. Gauge on dash matched pressure in tire so i dont think the hose is blocked or the gauge is bad.

Has to be either impeller issue or blockage elsewhere is what im guessing.

Any help???

 

[jerryjerry05]

I wouldn't worry so much about the pressure.
Sounds like you have plenty of water.

I bought a heat/temp gun on ebay for 16$
I'd get one and then do the temps all over the motor.
About the hottest spot should be the plugs(?)

The crud if any settles to the bottom and if there is any the lower part of the water jacket next to the bottom port cover
should/could be hot as no water or water flows slowly there.

What condition was the thermostat when you removed it?
Any build up or scale? See pics.

Take some temps. Post the results.

The thermo is 110d so your motor shouldn't get real hot..
The thermo switch is about 130d (I think) When it gets that temp the alarm goes off.
Maybe someone can post the actual temp of the switch?

 

[DunbarLtd]

Manual says thermal switch closes @ 160F. I know the horn sounds when grounded. I will have to take some temps when running to make sure its not overheating and the thermal side of the switch is working.

Tstat was not scaled up. I put new one in couple years back. Tested it just yesterday in hot water and its functioning properly. Closes like it should.

Im maybe thinking impeller might have issues maybe housing is leaking?? I didnt put sealant between housing and plate.

Maybe its leaking there???

I will probably take the head off just to make sure i guess. I think i can re-use the gasket.

 

[Simple_Man]

My 87 17' Bayliner capri does about 4200 rpm with a 17p prop runs ruffly 31mph. It sounds to me like your running fine.

 

[DunbarLtd]

My 87 17' Bayliner capri does about 4200 rpm with a 17p prop runs ruffly 31mph. It sounds to me like your running fine.

Interesting. Thanks for the input.

Have you changed the impeller? If so, I was wondering if it could leak where the pvc adapter on the housing slides over the copper water tube, even if its lined up correctly? I suppose its a tight fit but there no way to really confirm if its leaking there. I took a fine sandpaper and sanded the copper tubing because it had very minor corrosion, not pitted though.

I assume if it has water flow coming out of the tell tale then its fine. Its weird they didnt install anything on the motor that has to do with water flow. I suppose that was the purpose of the over heat buzzer. Id just like to have something give me an earlier warning that something isnt right before it actually over heats to the point where the alarm buzzes.

I havent had the alarm buzz yet but im concerned with the low pressure readings im getting after replacing the impeller.

 

[jerryjerry05]

17ft Bayliner (worked on hundreds) 85hp.
It should tach out about 53-5500 and get almost 40mph.
T@T working right? No whale tale?

If you doubt the pump and tube connection??
You can add a piece of hose3-5" long on the pump.
No buzzer: have you tested it?
Key on, ground the orange lead at the buss bar.
It should make the buzzie buzz.
I like to replace the buzzie with a motorcycle horn.
Much louder. Just make sure you get it wired right.

Install a pee tube. Top of the head is a silver plug.
Plumb it to that spot.

 

[DunbarLtd]

17ft Bayliner (worked on hundreds) 85hp.
It should tach out about 53-5500 and get almost 40mph.
T@T working right? No whale tale?

If you doubt the pump and tube connection??
You can add a piece of hose3-5" long on the pump.
No buzzer: have you tested it?
Key on, ground the orange lead at the buss bar.
It should make the buzzie buzz.
I like to replace the buzzie with a motorcycle horn.
Much louder. Just make sure you get it wired right.

Install a pee tube. Top of the head is a silver plug.
Plumb it to that spot.

If it should be doing 53-5500 then something is definitely wrong with this motor. Compression was 130 +/-5 on all three. I posted results on first post of this thread,. Maybe its still too low? Its either that or i have a spark issue and the cd boxes or coils are malfunctioning. Stator maybe. I dont have a dva so im dead in the water there. Only thing i can check is for spark with a spark tester and thats difficult to do at full speed.

Buzzer works fine when grounded. Horn is nice and loud and yes i replaced with motorcycle horn as well. Have to remove and test in hot water to make sure it gets continuity @ 160F.

Water pressure gauge is tapped into top of head just behind tstat. Is it possible the gauge hose can get air trapped in it and not read correctly? I never really thought of that until now. Maybe i should run the engine until it comes shooting out of the hose and then quickly connect it to the gauge??? probably get a little wet under there but itd get rid of the air id think...

Ive taken that hose off last time out and theres a brass barbed nipple plumbed. I think ill change it out to a 90 degree instead of straight barb because i think the hose is possibly kinking there as i have the hose routed down the side of the powerhead and then it makes its way down the gunwale and to the dash.

Its had decent water pressure before with it plumbed that way but I can see the hose starting to kink a little. Really doubt thats the issue though...

So with the water hose disconnected and the cover off the motor, water was shooting straight up and out of that nipple at cruising speed but its confusing because gauge was only reading around 6psi right before this test on my first run out. Down about 5psi before i changed the impeller. So somethings going on.

T@T work fine. Motor goes up and down and stays up for weeks. Had leak down problems but repaired the seals in the valve and its been fine for couple years now. I have adjusted the trim while wot many times and it does affect speed but only by a couple mph at most. Itll start to porpoise and then i trim it down a little and thats the happy spot. So yes it works like it should. Also Ive adjusted the exhaust snout so the boat tracks straight when the trim is adjusted properly.

No whale tail....

EDIT: I forgot to say when i replaced the impeller i found a 1" long chunk of the tip of an impeller vane sitting in the corner of the pump housing. Now the impeller that I replaced had all of its vanes in tact, so I have to assume whomever replaced the impeller before I bought the boat had an impeller get chewed up. Its very possible there could be other chewed up pieces of that old impeller lodged somewhere in the system and causing low flow.

If so....what the heck can i do about that if I dont know where the obstruction is???

 

[jerryjerry05]

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.