Force '89 125hp lacks power and top end speed

[Gearhard]

Hi,
My Force motor just doesn't seem to run very well. It doesn't have a good hole shot, and doesn't hit the WOT rpm's that it did when I first put a new power head on it. 3 years ago I replaced the power head and Checked the comp on all cyls, and it's still the same @ 150psi. I've replaced the stator, linked and synced the carbs and timing, checked timing, new plugs, rebuilt carbs, rebuilt fuel pump, and replaced fuel lines. When I first got it all back together it seemed to run fairly well, but performance has diminished over the past 3 years. Throttle and choke plates are fully open at WOT, throttle roller lines up between marks on cam, and timing set to 30 deg BTDC, but still only hit about 4200 rpms and 24 mph at WOT. Prop is 15p and boat is approx 1800 lbs. Magnet had to be re-glued in flywheel but was matched to old marks from before. Can anyone suggest what else I may have to check and/or correct? I'm running out of ideas and growing in frustration. Thanks!

 

[The Force power]

Hi,
My Force motor just doesn't seem to run very well. It doesn't have a good hole shot, and doesn't hit the WOT rpm's that it did when I first put a new power head on it. 3 years ago I replaced the power head and Checked the comp on all cyls, and it's still the same @ 150psi. I've replaced the stator, linked and synced the carbs and timing, checked timing, new plugs, rebuilt carbs, rebuilt fuel pump, and replaced fuel lines. When I first got it all back together it seemed to run fairly well, but performance has diminished over the past 3 years. Throttle and choke plates are fully open at WOT, throttle roller lines up between marks on cam, and timing set to 30 deg BTDC, but still only hit about 4200 rpms and 24 mph at WOT. Prop is 15p and boat is approx 1800 lbs. Magnet had to be re-glued in flywheel but was matched to old marks from before. Can anyone suggest what else I may have to check and/or correct? I'm running out of ideas and growing in frustration. Thanks!

Welcome to IBoats

When you say;
Replace Stator/new plugs/pump etc. etc.
When was this?? now or 3 years ago? then verify if all items are still good.
Check for RPM-drop on each Cylinder
I tend to think; its a intermittent spark issue
Below is a link to diagnose the ignition

https://www.outboardignition.com/page8.asp

 

[WinnerCougar74]

How old is the fuel pump. Many replace the diaphragm every year or 2.

 

[Gearhard]

Hi, and thanks welcome and the ignition link!
I have to admit that a lot of that was 3 years ago that I replaced the parts like the stator. Plugs are replaced usually twice a year, compression check every tuneup, tuneup every time it's not running well, water pump kit replaced every other year. I wasn't sure how often the fuel pump needed to have parts replaced. Coils and CD units have not been replaced. I'll try a cyl drop test and see what results I get. Are there other parts besides the diaphragm that should be replaced in the fuel pump? And are there any guidelines for how often the carburetors should be taken apart and serviced? New kits again for those also? Thanks again for any help, it's tough finding anyone that know much about this motor around here.

 

[jerryjerry05]

Try running with the cover off.
What's the compression results?
Is the linkage opening the butterflys like it should?

 

[Gearhard]

JerryJerry, engine runs the same with cover off or on. Compression 150psi +/- 2 on all cylinders. Butterflys fully open and horizontal at WOT. Pickup roller set between marks with throttle closed, timing tower disconnected. Recently saw a post on here where person said motor ran better (+ 8mph) with timing set improperly and butterflys 3/4 open. I don't know enough to play with changes like that to improve performance, willing to try at this point, but don't know where to start.

 

[Gearhard]

I have some more questions regarding my motor, if I may? If I do a drop cylinder test and start pulling off plug wires, is it still necessary to ground the unattached plug wire while the engine is running? If I do a drop cylinder test and start pulling off plug wires is it necessary to have the motor running and in water, or will muffs suffice? And at what RPM range should the drop test be done? Thanks for the help!

 

[MrMarty51]

I dont have the answers to Your questions, I’m only commenting that when a drp cylinder test is performed, a more accurate tachometer than the dash unit might be used.
the timing light I have, it also has a tach display and I think that would be more accurate than the dash unit.
someone that knows about these things please correct Me if this is wrong information.

 

[Gearhard]

MrMarty51
Thanks for the reply. I have a timing light that has a tach but it doesn't seem to work even as well as the dash tach. I am waiting on a tiny tach to arrive. Hopefully that will work.

 

[The Force power]

I dont have the answers to Your questions, I’m only commenting that when a drp cylinder test is performed, a more accurate tachometer than the dash unit might be used.
the timing light I have, it also has a tach display and I think that would be more accurate than the dash unit.
someone that knows about these things please correct Me if this is wrong information.

IF....you have a timing light with a built-in Tach. for a 2-stroke then I praise you for have the right tools:thumb:

 

[The Force power]

MrMarty51
Thanks for the reply. I have a timing light that has a tach but it doesn't seem to work even as well as the dash tach. I am waiting on a tiny tach to arrive. Hopefully that will work.

Most likely your timing-light is for a 4-stroke and that's why your readings are "off"

 

[The Force power]

If I do a drop cylinder test and start pulling off plug wires, is it still necessary to ground the unattached plug wire while the engine is running? If I do a drop cylinder test and start pulling off plug wires is it necessary to have the motor running and in water, or will muffs suffice? And at what RPM range should the drop test be done?

No, don't ground the plug-wire just unplug briefly & listen/ verify on tach. if RPM's are dropping?
No drop=no firing/running on that Cylinder

Make sure you have the right tool to unplug OR are standing on wood with thick gloves on! lol

This can be done on hose, running at idle-speed

 

[The Force power]

Butterflys fully open and horizontal at WOT. Pickup roller set between marks with throttle closed, timing tower disconnected.

Why & where from is the timing tower disconnected?

 

[Gearhard]

Why & where from is the timing tower disconnected?

Sorry, I meant that the timing tower was disconnected at the carb linkage to set the cam roller to the marks on the cam.

 

[Gearhard]

IF....you have a timing light with a built-in Tach. for a 2-stroke then I praise you for have the right tools:thumb:

Yes, one of my timing lights has a built in tach, supposedly for 2 or 4 cycle motors, but apparently not the greatest since the RPM readings tend to flicker. And I also have a couple of plastic plug wire pullers. Thanks for the info about the hose being adequate- and checking at idle speed.

 

[The Force power]

Yes, one of my timing lights has a built in tach, supposedly for 2 or 4 cycle motors, but apparently not the greatest since the RPM readings tend to flicker.

It is possible that it is picking up the signal from another plug cable if not positioned properly

 

[Gearhard]

I'm not sure if I found a problem that is causing my poor hole shot issue. After reading thru other posts, I found something that said timing should be set at 28° BTDC static and 30° dynamic. That is where I had been setting my timing to. But the post I was reading also had mention of a setting of 9° at idle speed. Today I checked the timing at idle speed and found it to be 9°, but it was 9° ATDC. The post didn't mention whether or not it should be set at ATDC or BTDC. I assume it should be 9° BTDC. Is this correct? 18° is a significant difference in timing. And there is mention in the post about bias although I'm not sure what this is, can someone please explain? Is there a way yo adjust the idle speed timing? Thanks for any help and clarification on this issue!

 

[Nordin]

If you have the Prestolite ignition system (two black or blue CDI modules and four black or blue ignition coils) you only set the timing at WOT, 28 dgr BTDC static at cranking speed.
The timing at idle will be what it will be. You set the idle speed to 700-800 RPM in water and in gear.
Idle speed screw is at the lower part at the timing tower.

I am not so familiar with the Mercury Thunderbolt ignition system which Mercury started to put on the Force engines in early 90:es but I think you set the idle at a timing about 8-9 dgr BTDC.

 

[Gearhard]

It is the blue prestolite ignition system. I have never seen anything about an idle timing technique for it. But 9° ATDC seems too late. At slower speeds, it cant have good power. But I don't know it that can be changed or if a new psrts (cdi) would help?

 

[jerryjerry05]

No idle timing.
Static timing.