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

[jerryjerry05]

You try what I suggested?

"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]

You try what I suggested?

"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."​

Not yet. But if it does and I feel like the throttle cable is adjusted with all the slack out, then what else could it be?

Nothing appears to be broken.

I will have to go buy a compression tester to see where it is in order to rule that out.

But Im assuming if compression was out of spec, it may not even run correctly?

 

[jerryjerry05]

You probably wouldn't get the speed your getting if the comp is low.

The physical limit of the shifter can be reached but the carb can be pushed further.
They are 2 systems working together to get WOT
The throttle can be adjusted and reach it's limit but the carb can open further.

 

[DunbarLtd]

You probably wouldn't get the speed your getting if the comp is low.

The physical limit of the shifter can be reached but the carb can be pushed further.
They are 2 systems working together to get WOT
The throttle can be adjusted and reach it's limit but the carb can open further.

Ok I understand what you mean.

I decided I would do a complete link and sync. Basically start over. Including the idle speed screw. So after all that I got to the lake and of course had to adjust the idle just so it stays running while in gear. All was well. Started and idled fine. Restarted ok.

After a short warm up i gave it wot and gps showed about 34mph. Oddly the pitch of the motor seems to have been lowered a bit. A buddy of mine even mentioned it to me.It used to whine louder @ wot. But didnt go any faster. I wonder if this has to do with the Decarboning?

But during the day on a few runs it wouldnt go above 30-31. It was kinda choppy that day so maybe thats it. I figured when i use more gas it gets lighter and I would get better speed but that wasnt the case much.

I will have to take it out again to see what happens.

Its possible I keep fouling plugs?

I only set the air screws to 1 turn out and have not messed with it. Honestly it scares me to mess with the screws and fine tune it. Ive never had to do it before and of all the info/videos ive seen i get the general idea but it seems like its something that takes experience because its a matter of listening to the motor and without any experience doing it, Im not so sure i can get it right.

Anyways thats the update.

 

[jerryjerry05]

You didn't say you tried what I suggested??

The air screws don't affect anything but low speed.

 

[DunbarLtd]

You didn't say you tried what I suggested??

The air screws don't affect anything but low speed.

I had a chance to get out today.

As usual start and idled fine until warmed up. I was able to go back there while a buddy drove and I could not push down on the throttle cam any whatsoever. Nor could I move the timing tower rod.

What I noticed is I initially got it to 30mph (+/- .5). Little chop today but basically perfect. So after I go check on the cam and get back in the driver seat, after slowing down to idle I then punched it again without turning the engine off and I then saw speeds of 33.5mph and that was the top speed for the day. That is with messing with the trim as well.

I ran about 6 miles at that speed. Shut it down, fished for 3 hours without using the motor at all. On the way back I had a somewhat moderate flat wake area i had to go through. So I idled for maybe 500 yards.

And so the on the way back I only saw 31.5. I did try to slow it down again but this time it did not creep back up. All I got out of it was about 31 tops.

On the way back its possible the wind was in my face but it wasnt much. So I dont know whats going on. I cant stand intermittent issues.

 

[DunbarLtd]

I put a dial indicator on the prop shaft and it was.006 out. I assume .002 is within spec. I must have tweaked the shaft a tad when i caused a small chip in the prop. I am not sure if this would cause the intermittent issue but i did notice some vibration on the floor today when @wot. It could be the new prop isnt balanced or the tweaked shaft. Ill take the prop to get looked at to rule that out. Just wanted to throw that in there. Thanks for the help.

 

[jerryjerry05]

The wobble shouldn't affect top speed.
Remove the prop.
Start on the hose, put in gear.
Then check the shaft visually.
You eye(my eye) can see if there is any bend.

I ran my boat(don't know how long) with a bent hub/prop.
Was changing oil and greasing the shaft.
As I walked past I spun the prop and it was a pretty bad wobble.
Didn't affect the top speed and no shaking??????

 

[DunbarLtd]

The wobble shouldn't affect top speed.
Remove the prop.
Start on the hose, put in gear.
Then check the shaft visually.
You eye(my eye) can see if there is any bend.

I ran my boat(don't know how long) with a bent hub/prop.
Was changing oil and greasing the shaft.
As I walked past I spun the prop and it was a pretty bad wobble.
Didn't affect the top speed and no shaking??????

Ok so if i cant get the cam to advance further and the shaft and prop are not the cause is there any other ideas here?

I think it has to do with the spark plugs loading up. Perhaps the 1 turn out setting on the air screws is just too rich? I understand this has no effect at speed because of the high speed jet is fixed, but it could load up the plugs idling and then affect spark? I dont know. Im at a loss here.

 

[jerryjerry05]

The 1 turn out is what the factory recommended.
Any more turned in and the motor will probably run lean and can damage the pistons.
You say you cleaned the fuel recirc system?
The screens can get clogged and cause the fuel to back up into the cyl.

 

[DunbarLtd]

The 1 turn out is what the factory recommended.
Any more turned in and the motor will probably run lean and can damage the pistons.
You say you cleaned the fuel recirc system?
The screens can get clogged and cause the fuel to back up into the cyl.

I cleaned it out season before last. Havent run decarb since just recently. Its possible its clogged again.And I dont mean it was clogged the first time i took the cover off. There was definitely some fragments in there but the screen was not clogged at all. Maybe after this decarb its clogged it up but id think if it was clogged i wouldnt even get that top speed i was getting. But ill pull the cover just to make sure. Hopefully figure it out. I may just have to deal with it. Because other than this small issue it runs fine.

 

[jerryjerry05]

The de-carb loosens the carbon build up and it can send crud to the screens.

 

[DunbarLtd]

The de-carb loosens the carbon build up and it can send crud to the screens.

I did some searching around and found that clogged screens affect the idle more than anything.

 

[DunbarLtd]

The de-carb loosens the carbon build up and it can send crud to the screens.

Hey Jerry,

I wanted to update this issue again. I had a chance to get out on the water yesterday morning. I thought Id throw this out there since now it has repeated itself. Again at first i didnt have much trouble starting and idling out past flat wake. While going to my spot i was able to get up to 34mph (GPS). So as usual we stopped and fished for around an hour.

Well after i started it up again and ran across the lake to a new spot the same thing happened. I lost 3 mph. Again I messed with the trim to make sure. And for the rest of the day it did not matter what i did i could not get it back up to speed. The engine sounds normal.

I think its interesting the same thing happened last time out. First run of the day and it reached max speed then after then it drops off and 3-4mph is lost. I am completely baffled on this one. I rechecked the throttle cam again and it doesnt move whatsoever even with moderate force pushing on it. I replaced the spark plugs just to see. Used same Champion UL18V.

Is there anything else you can think of? If not, I think I will just deal with it until maybe another issue pops up that is relevant.

Again I want to thank you for taking the time to reply. Always learn something new in this forum.

 

[jerryjerry05]

Sounds like you need to run it like it is.
Keep an eye on it, doing comp and spark checks.
You check the timing while your running it wide open?

 

[Tech Tony]

Maybe check your speedometer?

 

[DunbarLtd]

Maybe check your speedometer?

I have both dash speedo and gps on my humminbird 10. The dash speedo is off about 3 mph which is slower than gps. But the readings are consistent on both when i lose speed. This has now has happened maybe 4 times. Runs top speed first run of the day. Turn off motor. Then all of a sudden for some reason i lose 3-4 mph after that.

I dont know if compression test would make a difference. If compression was low, I prob wouldnt get to 34mph in the first place. This is such a weird issue. I looked all over the internet and asked some mechanics and everyone is clueless. These are the most annoying problems too.

But it runs decent enough to get on plane and runs smooth at 30mph. I know its just 4 mph difference and not a big deal but I hate not knowing what the cause of a problem is. Keeps me up at night lol

 

[DunbarLtd]

Sounds like you need to run it like it is.
Keep an eye on it, doing comp and spark checks.
You check the timing while your running it wide open?

Couple questions.

1. When I do the spark test is 7/16th jump good enough and do i just disconnect the plug and wire and crank or what? I have a proper spark tester btw.

2. I got to thinking and reading some other posts and i came across a post where someone mentioned their exhaust boot blew and water was inside the lower leg. Well my question here is when i take the cowl off after running for a while, i notice some water down inside the leg. I am assuming this is normal? If not, what is the usual cause of water getting in there?

3.To clarify, my exhaust boot is fine and does not leak water.

 

[jerryjerry05]

The boot is one place it can leak exhaust.
The other is the seal between the block and adaptor plate.
If it leaks it usually dies unless the covers off.

You have a tach? What's the rpm's at wide open?

 

[DunbarLtd]

The boot is one place it can leak exhaust.
The other is the seal between the block and adaptor plate.
If it leaks it usually dies unless the covers off.

You have a tach? What's the rpm's at wide open?

I tried the tiny tach but it malfunctioned somehow. This boat didnt come with a tach.