88 Force 85hp (3 cylinder). Engine sputters under heavy acceleration from idle.

[DunbarLtd]

I did a lot of searching and havent really seen this topic discussed much. So I wanted to start a new thread about this issue. I think I have an idea whats causing the problem but i figured id come over here and ask you guys.

After warming engine lets say first thing in morning, if i am idling out and then just immediately go full throttle it sputters or hesitates or bogs. Not sure how to describe it. But after a few seconds it will clear up and get on plane.

I believe it seems to do it more if i idle for long periods which to me sounds like a spark plug carbon issue but maybe there is another reason.

Otherwise, while running at any speed the engine runs smooth. Seems to only do it when from a stop or slowly idling. At 1/2 throttle i did not notice the problem under heavy acceleration.

Ive rebuilt the carbs before this season with new needles. Adjusted floats. Perhaps I have wrong float setting? I cant find documentation for these old Tillotsons. Maybe there is a model number on them???

I believe i set the floats just past parallel. So upside down the float sits just a tad higher than parallel. Perhaps the floats are too low and emptying the bowl when i accelerate heavily?

I even thought about bad primer bulb but ive inspected the inline clear filter(G-2 i believe) and it stays full so i think the fuel system is not leaking air and the check ball in working correctly but i dont really know how to test the primer bulb.

Any other ideas?

 

[redfury]

Bogging under heavy acceleration from idle and then clearing up is usually an indication of a mixture that is too rich. Try turning in your jets 1/16th a turn and keep at it until it clears up.

 

[SkiDad]

I agree. It’s most likely the idle fuel mixture screws. Set them all at 1-1/4 turn out from lightly seated. See what that does for you. Don’t go lower than one turn out. After you get it accelerating good the reset the idle to 800-850 while in forward gear (in the water)

 

[Nordin]

This is just normal for all old two strokers.
They do not burn all fuel especially at and after long idling.
Does not matter what brand of engine but some recirculate the fuel better then others.

If you idle for a long time it may foul the plugs and not clear up when accelerating, then you have to pull the plugs and clean then up by hand.

This is the problem with old school two stroker engines. They are dirty and can not full fill the emission reduction of today.
Todays two stroker has electronic control of the fuel and are not soo dirty to the environment.

 

[DunbarLtd]

Bogging under heavy acceleration from idle and then clearing up is usually an indication of a mixture that is too rich. Try turning in your jets 1/16th a turn and keep at it until it clears up.

I have them all 1 turn out as factory suggested. Im afraid a little more may lean it too much?

 

[DunbarLtd]

I agree. It’s most likely the idle fuel mixture screws. Set them all at 1-1/4 turn out from lightly seated. See what that does for you. Don’t go lower than one turn out. After you get it accelerating good the reset the idle to 800-850 while in forward gear (in the water)

Ive already set them all 1 turn out.

And I dont have a tach so i just set it to where it stays running after i put it in gear. Its a balance of just enough rpm and not getting a clunk when in gear. Right now i think i have it set maybe just a tad too low and sometimes it feels like it wants to die. I may adjust it more next time out. Ive had it set before to where it idled and went into gear perfectly.

But I did a complete link and sync recently and started over to make sure everything was set up correctly and part of that process i took the idle screw all the way out. Then on the water i kept adjusting til it would stay running when put into gear. I got it almost there but wanted to go fish. Next trip out i will spend some time and fine tune it. If the weather works out it looks like Wednesday will be a good day to go out.

 

[DunbarLtd]

This is just normal for all old two strokers.
They do not burn all fuel especially at and after long idling.
Does not matter what brand of engine but some recirculate the fuel better then others.

If you idle for a long time it may foul the plugs and not clear up when accelerating, then you have to pull the plugs and clean then up by hand.

This is the problem with old school two stroker engines. They are dirty and can not full fill the emission reduction of today.
Todays two stroker has electronic control of the fuel and are not soo dirty to the environment.

Ive recently ran some Power tune decarbing spray into the cylinders and let sit overnight. But it has been about 5 outings since then. Is it possible the re circulation system and screens are now clogged? Ive taken the dog bone off before and cleaned the screens out. It was caked with carbon deposits but the screens were not completely blocked up. Ive done some searching and ive read that clogged systems really only affect idle but maybe it affects acceleration too? I dont really know what to believe.

But I do hear ya. Since Ive had the motor over the past 4 years I could never idle for too long. Ive had to take the plugs out several time and clean them and when i think about it, i believe it lost the sputter. I am going to idle out next time. Clean the plugs and then immediately start it while still warm and gun it and see what happens. If it still does this then I think we can confirm its not oily plugs causing the problem?

 

[jerryjerry05]

Unless the plugs are completely covered in carbon they should??? work.

The floats need to be level when upside down.

The factory suggests 1 turn out on the air screws.
But that doesn't always work best
Had a customer with a 1984 85hp the motor wouldn't idle until the screws were almost 3 turns out????

They sell a small tach that hooks on a plug wire.
I bought mine for about 16$

If the idles too low that can cause the problem.
You said:

(And I dont have a tach so i just set it to where it stays running after i put it in gear. Its a balance of just enough rpm and not getting a clunk when in gear. Right now i think i have it set maybe just a tad too low and sometimes it feels like it wants to die.)​

Clunk is ok. BANG is not

 

[DunbarLtd]

Thanks Jerry. I dont have an issue with the idel. Once I get the idle speed screw adjusted right, itll idle just fine @ 1 turn out.
Are you suggesting a low idle can cause a bogging issue when going full throttle from low speed? Because thats the main issue. And good to know on the floats. I am going to take them all off again and double check to make sure.

Ive seen some posts about the drop level on the float and from what ive read you want it about 1/8" before it touched the bottom of the bowl or as the manual says, just before it touches the side of the carb? Is this correct because i have not adjusted drop at all yet. Doubt this is the problem but id like them set up properly anyways.

 

[jerryjerry05]

The drop's not as important as the float's being level.
It just makes the float open/close more often.

Yes if the idles not right it can affect the take off.
The idle rpm's need to be right.
Get a Tiny Tach or equivalent.
On hose, about 1150-1200
In water in gear moving, 800 rpms.

 

[SkiDad]

one thing that was not mentioned in your plug type - are you running NGK BUHX ? That ran the best in my force and idled the best too.

 

[racerone]

Slow speed needles are often adjusted to get a nice idle.----That makes the motor run smooth and sounds pleasant to the ears.----But that often is TOO LEAN for good acceleration.----Opening the needles 1/8 turn till stumble / bogging disappears is the " no money spent " solution.

 

[DunbarLtd]

one thing that was not mentioned in your plug type - are you running ngk buhx ? That ran the best in my force and idled the best too.

Champion ul18v. I called Mercury and that what they suggested. Not saying this engine runs best on it just saying thats what they have listed.

 

[DunbarLtd]

Slow speed needles are often adjusted to get a nice idle.----That makes the motor run smooth and sounds pleasant to the ears.----But that often is TOO LEAN for good acceleration.----Opening the needles 1/8 turn till stumble / bogging disappears is the " no money spent " solution.

So, If I understand this correctly, when you turn the idle air screw counterclockwise you are effectively allowing more fuel and creating a rich condition? Which is fine but I suppose if I have it set too lean this could possibly be the cause of the studder? Its basically starving for fuel...that makes sense.

The engine demands more fuel because of the throttle plates being wide open, which cause maximum amount of air flow. More air = more fuel.

I can see how it makes sense to open the screw and allow more fuel in that situation. And the benefit will also be a well lubed engine. I will sacrifice a perfect idle for better hole shot performance for sure.

But...

If the air screw isnt set correctly then how does it not create a problem @ WOT. When i am going full speed it doesnt hiccup in the slightest. Ive ran 5+ miles last time out and it was super smooth the entire trip.

Id have to assume, if the throttle plates are fully open, just like they are during a holeshot, then if the carb wasnt adjusted correctly....the same symptom would occur whether @ WOT or during a holeshot???

But maybe Im blockheaded and not getting it?

I have them all exactly set 1 turn out now. I will try the richer setting.

What is the sequence? Do I start at the bottom or the top first? Does it matter?

I understand I need to wait some time to allow the fuel to be burnt off from the old setting before i adjust again.

 

[racerone]

Some will argue on this.-----I recommend you open the low speed mixture screws.----Cost nothing to try that.----No need to overthink this.-------When you suddenly open the throttle plates the air flow DOES NOT suddenly increase.----It takes time.-----No wonder that fuel injection has become so popular.-----The computer does all the thinking for you !-----Sorry to be so blunt here.

 

[The Force power]

as Raceone already said; the low speed needle" is exactly that, it only controls the fuel/air mixture when idle
Once the shutters on the carb open they don't affect the fuel mixture.

and no it does not matter in what order but do it rapidly and make sure they are even

 

[DunbarLtd]

Some will argue on this.-----I recommend you open the low speed mixture screws.----Cost nothing to try that.----No need to overthink this.-------When you suddenly open the throttle plates the air flow DOES NOT suddenly increase.----It takes time.-----No wonder that fuel injection has become so popular.-----The computer does all the thinking for you !-----Sorry to be so blunt here.

No worries I have thick skin. Im still learning so i hope i dont sound too ignorant. Anyways I will experiment with the air screws and start turning them out 1/8th at a time to see if it helps. Thanks for the help.

 

[DunbarLtd]

as Raceone already said; the low speed needle" is exactly that, it only controls the fuel/air mixture when idle
Once the shutters on the carb open they don't affect the fuel mixture.

and no it does not matter in what order but do it rapidly and make sure they are even

Then what does the air screw have to do with the studdering problem if they are out of the equation at that point?

I know what you mean but its not making sense to me.

If I dont have a problem when im at full speed and the plates are wide open, why would i have a problem if i all of a sudden gave it full throttle from a 3mph idle, effectively opening the throttle plates as far as they are during WOT?

Is it not requiring the same amount of fuel in both scenarios or have i had one too many tonight?

 

[Nordin]

I would suggest you to set the air/fuel screws at 1 1/8 out from lightly seated.
Then fine tune each carb starting from top if you want or let them be at 1 1/8 turn.
To lean and you risk to melt a piston.

Remember that the low speed circuit and high speed circuit do not have exact limits.
They over lap when accelerating and deaccelerating.

 

[DunbarLtd]

I would suggest you to set the air/fuel screws at 1 1/8 out from lightly seated.
Then fine tune each carb starting from top if you want or let them be at 1 1/8 turn.
To lean and you risk to melt a piston.

Remember that the low speed circuit and high speed circuit do not have exact limits.
They over lap when accelerating and deaccelerating.

Thnks Nordin.Yea I couldnt find anything on how these carbs on these motors actually work. I guess if there is overlap then its not exactly black and white. Ill try the air screw adjustments.

Also just for clarification. When I unscrew the air screw what is happening in these carbs? Am I just allowing more air in or more fuel. I think thats whats confusing me the most. Im used to carbs having high and low adjustments but these just have one screw so im not sure what its actually changing??? Fuel or air?