1988 Forcce 85hp Losing 4mph top speed after decarbing???

[DunbarLtd]

I've had this outboard for about 3 years now and havent done much to it. Ran pretty good when i bought it. Just maintenance repairs like hoses and stuff. I did rebuild the carbs last year. Also ran some Quicksilver power tune through the carbs/cylinder soak last year. Was able to get up to 35mph all year. No issues really.

Well recently I decided to do the annual decarbing with the same stuff i have been using, but this time after letting it sit the typical 12 hours (flooded each cylinder with power tune overnight), i am noticing i have lost some power @wot and its maybe hitting 31mph. My trim works fine and ive messed with it to no avail.

So naturally as one would do, you start troubleshooting and so I checked some things so far.

Carbs opening fully? CHECK
Fuel filter still clean? CHECK
Air mixture screws are turned ONE TURN OUT.

Thats about it so far. I dont have a tach so im not sure whats rpms are @ wot. Sounds different though. Not as high pitched as usual.

Also I put a new prop on which is the same exact size and pitch. I had only one prop for a while and last time out got a dime sized chunk tore off one of the blades so i just decided to spend the extra money and get a solas rubex 13.5" x 17p and that way ill have a spare on board. Coincidentally, the same day i had the prop damage is the exact day after i sprayed power tune in the cylinders. Im not convinced this is a prop issue because even with the new prop its still topping out at 31mph.

Currently using UL18V plugs. They are getting like black carbon "chunks" on them even after wot runs. Ive done about 3 longish 10 minute runs since decarbing.

Are the UL18V's too cold??? Of course they are a little oily as usual. I run 50:1 quicksilver premium tcw-3 oil. 1oz of quick tune and 2 caps of star tron for every 5 gallons. I use 5 gal cans and fill up by hand.

The motor does NOT cut out at full power. It definitely doesnt sound the same though. Its about an octave or two lower than im used to hearing when wide open.

Any help is appreciated. Thanks!

 

[GA_Boater]

You have quite a list of things. When did you lose the 4MPH? A little time frame sequence might help.

Is the prop exactly the same Solas Rubex as the old one. Diameter and pitch may be the same, but the blade shape and cup can be different.

On the mixture screws - Is 1 turn a ballpark or the fine tune adjustment setting in the water and in gear? The screws won't affect WOT, only starting and idle.

 

[DunbarLtd]

Time frame:

Sprayed power tune in all 3 cylinders. Let sit overnight for around 12 hours.

Very next day went out to the lake to burn out the carbon. Started it up. Of course, smoked like crazy. Idled out and then ran it about half throttle for about 3 miles, then tried to crank it up to wot. At that time it had the original prop on it, undamaged. I noticed right away it would not reach top speed. I figured it was because the power tune and it had to burn it all out of there. The night before when i sprayed the power tune i cleaned all the plugs.

So on the way to my spot to fish i noticed i wasnt getting much speed with throttle 100%. I think i maybe got 25 mph out of it on the way there. So i get there, fish for couple hours, mainly on the trolling motor. I did idle around in the area a couple times with the motor. But before i left i cleaned the plugs again. On the way back from the spot its like 5 miles to the dock it did not want to get more than about 30mph.

Now. I get home and notice the prop damage. Buy new one, put it in. Also again clean the plugs because they had burnt carbon pieces on them. I figured this was a result of running power tune.

Go to the lake again just yesterday which is Monday, 25th march. . Between the two trips i think 4 days went by. So i go out yesterday. It started ok and idled ok. Didnt smoke quite as much. After i get it on plane i noticed it wouldnt break 30mph. Again same thing on way back home on prior trip. Thats when i realized something going on.

I used power tune last year and dont remember having this issue but i sprayed the power tune through the carbs last time. This time I didnt and sprayed it in the cylinders.

I doubt the prop is the issue because it did the same thing with the old prop before it got a chip in it. Wouldnt go past 30mph. As in old i mean the original prop the boat came with which is just a mercury prop i believe.

Hope that clears it up. And yes the dimensions on the props are the same.

Also I am not sure at what point the blade was chipped during that first trip. But Im still convinced its not the prop. I wish i had a tach then i could have more information to go on.

It did 35mph wot with 1 turn out on carb screw. That is not a fine tune because I have not tried to fine tune it. It idles perfect. I was just adding that in there for more information.

 

[Nordin]

Difficult to say what has happened, but I would suggest you to check the compression in the cylinders so you have something to start with.
As you used Power tune you have cleaned up the pistons/rings from carbone and you may have affect the rings to seal against the cylinder walls.
The rings can catch the edges of the exhaust ports and you may have cleaned the walls from to much oil..

I am not a fan of decarbing engines and I used to run my engines with different RPMs and not troll so much.
The two strokers do not want to run at low troll RPMs for longer periods as the oil would not burn so good and start to build up carbone..

But start with checking the compression, then you have a start point to go from.

 

[jerryjerry05]

The powertune shouldn't hurt.

The one turn out on the air screws is what the factory suggested and it only affects
the low speed.

Like Nordin suggested : compression test.
Then clean the carbs.
When you did the decarb? did you clean the recirc system?
The dog bone shaped cover on the intake side, after a decarb it can get clogged and block
the system and cause problems with fuel delivery.

You check the linkage? sometimes the timer base connector breaks and when under full throttle
the break opens and the timing doesn't advance.

 

[DunbarLtd]

I havent messed with the timing advance linkage yet. Not sure where that is exactly. Im assuming I can find it in the manual?

And I thought about the recirc system. Ive cleaned the screen couple seasons ago but maybe thats it.

Compression test is probably a good idea. Thanks for the ideas.

 

[DunbarLtd]

Ive noticed something today while messing with it. When i squeeze the bulb the middle carbs leaks pretty good. I think the lower carb is leaking as well.

Is this normal? I am using an inline fule filter I think G12 or whatever walls carries. I noticed while pumping the bulb the filter does not completely fill all the way up. Only about 3/4 but the bulb is getting hard. And when it gets hard, the carb leaks fuel out of the throat.

Im assuming this has to do with the float setting or the needle seat/seal not sealing? Or is the dripping of fuel normal when you pump the bulb til hard and then try to keep pumping?

I would think when the bulb is hard even if you keep pumping the carbs should not leak. I just rebuilt the carbs last year with new float needles. I am pretty sure i set the float to parallel.

Any ideas?

 

[DunbarLtd]

Cleaned the carbs tonight and tested one at a time and im confident they dont leak. I adjusted the floats again. I think i may have had them set up to allow too much fuel in and maybe the needle couldnt seat. I know the middle carb actually had the hinge pin slide out on one end and the float was wonky. Maybe that was the issue, im not sure but it leaked like a sieve when i primed. Now its dry when pumping.

They are now all set the same. I actually set them up with the non hinged side just a tad higher than the hinged side. Hopefully that will still allow enough fuel into the bowl?

Question: What actually happens to the running condition when there isnt enough fuel in the bowls because the floats arent set low enough?

Also I inspected the timing link and everything in that region looks fine to me. The plastic (where the timing adjustment threaded "bolt" is) isnt cracked and its connected at the bottom as well. Looks like it is functioning correctly.

Ill have to pick up a compression tester tomorrow and check it out. Thanks for the advice guys.

 

[jerryjerry05]

The G-12 won't fill completely unless it's in a vertical position(doesn't hurt a thing)
The motor will bog if one cyl/carb doesn't have enough fuel.
What manual? Try to get a factory book..
The aftermarket, Clymer,Seloc have some info but lack the specifics the OEM book has.

The floats need to be level and the drop has the float almost touching the body.

Compression test, Harbor Freight is good for some tools but the comp testers usually read wrong.
But if that's all you have??
The results should be within 5# of each other.

 

[DunbarLtd]

Alright thank you sir. I will look into it.

 

[DunbarLtd]

The G-12 won't fill completely unless it's in a vertical position(doesn't hurt a thing)
The motor will bog if one cyl/carb doesn't have enough fuel.
What manual? Try to get a factory book..
The aftermarket, Clymer,Seloc have some info but lack the specifics the OEM book has.

The floats need to be level and the drop has the float almost touching the body.

Compression test, Harbor Freight is good for some tools but the comp testers usually read wrong.
But if that's all you have??
The results should be within 5# of each other.

OK I tested the boat out today. Started up and ran fine. I guess I just had to get those carbs out and clean em up and adjust the floats. I got it up to about 34mph...

BUT...theres an interesting thing happening. When i got it up to WOT initially, i could only get 30mph out of it again. Then i remembered this weird thing I was doing and its been this way for several months and I just cant figure it out.

This is what happens. Im going along at wot about 30mph, then randomly one day for no reason i shifted into neutral and let it slow down to about 20ish or so and then immediately gave it full throttle. What happens when i do this is i gain that extra 4 mph ive been missing.

Very strange.

Now if im cruising at wot and just simply slow down and go back to full throttle, it doesnt get to max speed. I have to actually put it in neutral and slow down to around mid 20's and then gun it again. Thats the only way itll hit max speed to about 34-35mph.

Sounds weird but it is what it is. Ive never heard of anything like it. Would it have to do with gears perhaps or what? Im not sure. I know for a fact the carbs are fully open before i do the kill it and gun it trick because ive had the intake air shroud off and looked into the mouth of the carbs while at wot and they were wide open. I thought maybe it was a carb issue but now Im stumped as to how i can get it to go to 34mph only if i shift into neutral then immediately full throttle again.

Other than that i think its running well. Only other thing I noticed was a lot of black oil dripping from lower unit but it did that last time i ran power tune through it so i assume thats all the gunk being burned out.

I ran wot for like 10-15 minutes and it didnt skip a beat except that weird throttle issue.

Any ideas???

 

[QBhoy]

Going by your last post...I’d be looking at the throttle cable for being stretched or loose at any connections. Also look for wear on the linkages and butterflies.
Worth mentioning that my boat will loose 4mph on any given day depending on a lot of things.
Weather
people on board
hull condition
fuel level
temperature
Bimini on or off
where people are sitting
how much beer is in the ski locker

 

[jerryjerry05]

That sounds like a linkage,cable problem.
You can try taking the cover off and go for a ride.
Then when at full throttle push the throttle cam all the way forward and see if the motor
picks up.

 

[DunbarLtd]

That sounds like a linkage,cable problem.
You can try taking the cover off and go for a ride.
Then when at full throttle push the throttle cam all the way forward and see if the motor
picks up.

Good idea. Ill try that next time out. I know in the garage when i throw the handle all the way forward i can see the carbs fully open but maybe that changes out there somehow. And also I made sure the throttle control is not recoiling from being too loose. I had that issue before and adjusted it so the control stays all the way forward without having to hold it there.

 

[jerryjerry05]

Your butterflys can go past horizontal and still work.

 

[DunbarLtd]

Your butterflys can go past horizontal and still work.

Not sure I understand what you mean? I understand the butterflies dont have to be exactly 90 degrees open to achieve maximum speed, but Im not sure what you are meaning? Thanks.

 

[jerryjerry05]

Find a parts diagram that shows the linkage where it connects to the carb.
Look for a part called the throttle cam. It's the part that pushes on the roller that opens the butterfly's.

 

[DunbarLtd]

Find a parts diagram that shows the linkage where it connects to the carb.
Look for a part called the throttle cam. It's the part that pushes on the roller that opens the butterfly's.

Ok I see what you mean now. You are saying to push down on the cam and that when doing so if it makes the butterflies go past horizontal it will still work. This makes sense and thank you.

Also Im wondering if it may have anything to do with the timing advance? And maybe the rod isnt being pushed to its limit where it needs to?

My thinking is that if the butterflies are already completely open when the controls are all the way forward, then what would I be accomplishing by getting more travel from the cam, essentially opening the butterflies even more?

Im guessing it could advance the timing or am i missing something?

 

[The Force power]

Hi Dunbarltd,

You should check out; Frank's sticky on link & sync.(with the control cable disconnected)

Set timing first
Generally speaking; the advance is really really close to (or at max) when the butterflies start to open & "ideally" they sit perfectly horizontal at W.O.T.(according the Brunswick manual it can affect the performance)

I'm not contradicting Jerryjerry05 words or try to confuse you by any means!!
Set the timing & carbs. first, then re-connect the controls; adjusted to your setting you just made (after verifying they are correct.

keep us posted

 

[DunbarLtd]

Hi Dunbarltd,

You should check out; Frank's sticky on link & sync.(with the control cable disconnected)

Set timing first
Generally speaking; the advance is really really close to (or at max) when the butterflies start to open & "ideally" they sit perfectly horizontal at W.O.T.(according the Brunswick manual it can affect the performance)

I'm not contradicting Jerryjerry05 words or try to confuse you by any means!!
Set the timing & carbs. first, then re-connect the controls; adjusted to your setting you just made (after verifying they are correct.

keep us posted

Static 28 degrees? Dynamic 30? Is this correct? I checked the TDC mark on the flywheel and its exactly on ZERO, where it should be but I suppose that doesnt mean the timing is necessarily correct.

And thanks for your reply. Any bit of info I get is a plus.