Hints for setting idle mix on 1989 Force 85hp

[dougrie]

I have a 1989 85hp Force on a 17' Dateline Bounty. 3 months in to ownership and nearly ready to launch however I still haven't resolved one last niggling issue: it seems to be running pretty rich at idle, and leaving plugs fairly oily (not carbon'd up, just dirty looking). I've got it in a tank so can't check behaviour under power yet. Anyway, I did some proper measurements this evening and at 900rpm in neutral it's burning about 10 litres/hour (about 2.5 US gal I think?). No sign of leaks, nor of blowback from the carbs (I checked the reeds, which are in good condition), so I'm sure it's all going through the cylinders. Compression about 115-125 across all. Cleaned carbs (twice) and rebuilt fuel pump - diaphragm looks sound. I've tried adjusting idle mix screws but to be honest I'm struggling to pick out much difference in engine tone when I adjust each of the three carbs, and I'm a little nervous in case I set it too lean as I've heard that these engines can burn pistons. Can anybody point me to a good YouTube video, or suggest techniques to me? (Or alternatively, reassure me that it's a reasonable fuel consumption at idle?)

Also, if anybody can suggest a decent budget fuel flow meter that'd be great...

Thanks all for your help!

 

[Nordin]

Two strokers do not burn all fuel and specially at idle.
Oil plugs from idling for long time is normal.
The settings of the air/fuel mixture screws are from about 1-1,5 turn out from lightly seated.
Sometime more then 1,5 turn is necessary.
If you do not set them less then 1 turn out you are on the safe side.
There is a sticker at the top of this forum from Frank A how to tune the carbs. It is called link and sync.
One thing you can do that maybe will improve oily plugs from idling is to clean the fuel recirculation system.
At star side of the engine there is a cover that looks like a dogbone.
Under the cover there are three screens that maybe are glogged with gunk (carbone and other residue from burned fuel) and they has to be clean out. You can clean them with carb cleaner and low pressure air.
Be careful when moving the cover. The gaskets might break and you have to replace them. Sometimes they do not break and you can reuse them by coat them with light gasket glue such as Loctite Form a gasket.

 

[dougrie]

Thanks Nordin. Yes, watched Frank's video which was very helpful but unfortunately didn't cover idle screw setting. Gave the recirc system a good clean already and yeah, it was filthy. Your point about not burning all fuel is a fair one. Maybe I need to get it in the water.

 

[racerone]

I think 10 liters / hr is too much.----Start engine.-----Turn each low speed screw all the way in and report if engine responds in any way to that adjustment.

 

[jerryjerry05]

The factory in 1989-90 produced a bulletin about the air screws settings.
They said set the screws at 1 turn out and leave them there.
Unfortunately not all motors can run at that setting
My twin 88 85's seemed to work good at that setting, some won't run unless they're out 3 turns.

Start motor, in the water, set all screws at 1 1/2 turn.
Top carb: turn the screw in 1/8th turn and wait 10-15 seconds.
Repeat until the motor bucks, stalls, changes tone, then back out 1/2 turn.
Repeat on the others.
I usually do it twice.

Myself I've never seen any specs (gas usage)on what the motor should use.
It varies a lot, depending on the driver, load etc.
I know my boat got 2.3 mpg. Under normal operation.
The harder you push it the worse it gets.

 

[dougrie]

The factory in 1989-90 produced a bulletin about the air screws settings.
They said set the screws at 1 turn out and leave them there.
Unfortunately not all motors can run at that setting
My twin 88 85's seemed to work good at that setting, some won't run unless they're out 3 turns.

Start motor, in the water, set all screws at 1 1/2 turn.
Top carb: turn the screw in 1/8th turn and wait 10-15 seconds.
Repeat until the motor bucks, stalls, changes tone, then back out 1/2 turn.
Repeat on the others.
I usually do it twice.

Myself I've never seen any specs (gas usage)on what the motor should use.
It varies a lot, depending on the driver, load etc.
I know my boat got 2.3 mpg. Under normal operation.
The harder you push it the worse it gets.

Thanks, that actually really helps. When I tried setting the screws I was checking for plug fouling and top carb needed to be out 2 turns before it stopped blackening all the time. Reading your suggestions though I think i wasn't giving the motor long enough to settle after each adjustment. Will try again & take my time.

2-3mpg sounds consistent with what everybody else says so I'm expecting that once I'm on the water. Just a bit bothered about it drinking so fast when it's doing nothing at all. But I suppose, given that it's different jets for idle vs WOT, idle consumption doesn't predict consumption under power anyway - right?

 

[The Force power]

THIS WAS WRTTEN BY THE LATE FRANK A.

1.Disconnect the ball link to the carb cam at the timing tower. Disconnecting at the cam risks bending the cam. Move the cam away from the carb roller.
2. Loosen the screw(s) on the aluminum tie bar and let all carbs close completely, then tighten again.
3. Set the cam so that the scribed line is pointing directly at the black roller on the carb lever. If the cam has two closely spaced lines, set the black roller directly between them.
4. The black roller is held with an offset screw and nut. Loosen the nut and turn the screw until the black roller JUST touches the cam. Tighten the nut and re-attach the ball link maintaining the scribed line at the roller.
5. Adjust the ball link so that at full throttle the bottom carb butterfly opens substantially horizontally. Adjust the aluminum tie bar so all carb butterflies open equally at full throttle. They need not be perfect but should be rather close to horizontal for best performance.
6. Adjust timing to 28 degrees before top dead center at full throttle.
7. Adjust idle speed to 700-750 RPM in the water in forward gear. Do this with the screw on the bottom of the timing tower. Loosen the locknut and adjust. Screwing in increases idle speed. Do this in small increments and let the engine rev and adjust itself before the next adjustment. A little goes a long way here. When correct, tighten the nut. Note that the scribed line on the roller will now be (usually) below the black roller a bit.
8. NOW we adjust the mixture on the carbs. Set all low speed needles to about 1 1/4 turns out from lightly seated. Do not force as this will damage either the needles or the seats.
8A. With the engine idling in neutral, turn each the needles in equally about 1/8 turn at a time. Give the engine a couple of seconds between each adjustment to stabilize. Adjust until the engine either "sags" or stalls. Note this setting.
8B. Now go the opposite direction. Adjust until the engine runs rough, burbles, or stalls. Note this setting.
8C. Set all needles to the average between the two settings: That is, for example, if it stalled at 3/4 turn out and burbled at 1 1/4 out then set all needles to 1 turn out.
8D. Readjust idle speed to 700-750 RPM.
9. Take the boat out on the water and do a "hole shot"--Full throttle acceleration from a stop. If the engine "sags" then recovers and picks-up it is too lean. Open the needles about 1/16 turn at a time until the engine accelerates with no hesitation.
If the engine sputters or coughs or burbles, then clears itself and accelerates, it is too rich. Close the needles about 1/16 turn at a time until the engine accelerates smoothly.

10. I can NOT stress this enough! NEVER set the low speed needles less that 1 turns out no matter how poor the idle or acceleration. To do so will run the engine too lean and detonation and melted pistons at or near full throttle operation will result.

 

[Nordin]

Thank you The Force power!
It was that one I wanted to refer to, not the video.
The procedure is to long to wright down every time someone call for how to adjust the carbs.

 

[jerryjerry05]

Thanks, that actually really helps. When I tried setting the screws I was checking for plug fouling and top carb needed to be out 2 turns before it stopped blackening all the time. Reading your suggestions though I think i wasn't giving the motor long enough to settle after each adjustment. Will try again & take my time.

2-3mpg sounds consistent with what everybody else says so I'm expecting that once I'm on the water. Just a bit bothered about it drinking so fast when it's doing nothing at all. But I suppose, given that it's different jets for idle vs WOT, idle consumption doesn't predict consumption under power anyway - right?

These motors aren't made for slow operation and the plugs will foul after time. If you set them right for low speed they don't run great at high speed and vice-versa.

 

[The Force power]

Thank you The Force power!
It was that one I wanted to refer to, not the video.
The procedure is to long to wright down every time someone call for how to adjust the carbs.

When confirmed that all ignition-components are good & this is followed precisely; the motor should run! (this was a life saver for me many times & I keep a printed copy together with the manual)

 

[dougrie]

Thanks, that is a great guide. I'll do this today. So screw in for lean, out for rich... is that right? Sounds like that's the other way around from some other manufacturers? Good info to have.

 

[dougrie]

Thanks again everyone; the advice really helped. I spent some time tuning the old girl tonight and it's now idling sweetly with mix screws all at 1 1/3 turn out, at 750 in gear consuming 6 litres per hour. Out of gear at 850 it's taking a little over 7. I'm fairly happy with that. Just one job left, giving the boat a good wash, then I'm taking her to the marina tomorrow for her first shot in the Clyde - wish me luck!