Force 125 a bit rough at times...

[fmt2bx]

Idle smooth, WOT smooth and getting about 35mph (byliner 19 capri), however i'd say around 1/3 throttle the engine sounds rough and getting some vibrations. What do you think, Fuel? Timing?
Thanks
Fmt

 

[pnwboat]

At certain RPM's like around 1500 to 2000, it's common for the 125HP motors that were made in the late 1980's to sound/feel a little rougher than it does at lower or higher RPM's. If it's running and starting fine, then I wouldn't mess too much with it. Having sid that, it's always good practice to replace the fuel pump diaphragm every few years (as well as the water pump impeller). Might also want to check the compression.

 

[SkiDad]

1/3 throttle is bad for gas mileage - 1/2 -3/4 would be much better. Does it accelerate through that rough rpm area fine if you punch it ?

 

[Jiggz]

I have the same '89-125HP and when I first had it, it had the same problem at around 1500~2000 RPM. I tried many things to smoothen it starting with fine adjustment of the air-fuel mixture screw on both carbs, checking for arc overs on plug boots and also cleaning the fuel recirc system. The one thing that actually gave me the most improvement is with the use of NGK BUHX spark plugs. The old plugs were Champions UL18V which are also the correct type for this motor.

 

[jerryjerry05]

Do a compression test.
Clean the carbs.
Check the reeds while the carbs are off.
Then set the air screw on the carbs.
Rebuild the fuel pump.
Check for water in the fuel.
Timing, usually if you don't touch the timing or change anything the timing doesn't move.

 

[fmt2bx]

At certain RPM's like around 1500 to 2000, it's common for the 125HP motors that were made in the late 1980's to sound/feel a little rougher than it does at lower or higher RPM's. If it's running and starting fine, then I wouldn't mess too much with it. Having sid that, it's always good practice to replace the fuel pump diaphragm every few years (as well as the water pump impeller). Might also want to check the compression.

Ok thanks. I ll check the compression.

 

[fmt2bx]

1/3 throttle is bad for gas mileage - 1/2 -3/4 would be much better. Does it accelerate through that rough rpm area fine if you punch it ?

Yes it accelerates out of that area without any problem.
Thanks

 

[fmt2bx]

I have the same '89-125HP and when I first had it, it had the same problem at around 1500~2000 RPM. I tried many things to smoothen it starting with fine adjustment of the air-fuel mixture screw on both carbs, checking for arc overs on plug boots and also cleaning the fuel recirc system. The one thing that actually gave me the most improvement is with the use of NGK BUHX spark plugs. The old plugs were Champions UL18V which are also the correct type for this motor.

Thanks Jiggz, I have theNGK BUHX plugs on it. It seems odd that this 1500/2000 RPM range exhibits problems. I would think that if you have spark at 800 and 5000 you should get spark at 1500 right? I would have thought that it should have been a fuel problem. From what I understand, seems like the 2 carbs are acting in parallel via rods. Could it be out of adjustment? Like one carb might be too reach or lean compare to the other?
How do you clean the fuel recirc system?

Thanks again.

 

[Frank Acampora]

The roughness you are experiencing is common on multi-carb Chrysler and Force engines It will vary a bit in RPM from engine to engine but is almost always there, The carbs are--compared to older auto carbs-- almost dirt simple. The venturi will not function and suck fuel until a certain amount of air is passing through it. Thus there is a low speed circuit for operation at lower RPM. The roughness occurs at the transition from low speed circuit to high speed.

 

[fmt2bx]

The roughness you are experiencing is common on multi-carb Chrysler and Force engines It will vary a bit in RPM from engine to engine but is almost always there, The carbs are--compared to older auto carbs-- almost dirt simple. The venturi will not function and suck fuel until a certain amount of air is passing through it. Thus there is a low speed circuit for operation at lower RPM. The roughness occurs at the transition from low speed circuit to high speed.

Thank you Frank, I won't be chasing this gremling then, I'll adopt him instead.

 

[fmt2bx]

We got our boat 2 weeks ago and are first time boat owner here. I had read about the Force engine and its bad reputation on diverse forum but I have to say, this motor is 30 years old and still running. I stopped by a marine shop the other day and from what I could see, lots of much newer (known for their reliability !?!) engine sitting for repair.
I kinda like this older technology.
Thanks to everyone here on this forum, it makes this Boat Owner experience soooo much easier.
Fmt

 

[Jiggz]

If you look around the fuel pump unit, underneath are short hoses running from cylinder to another. These are hoses for the fuel recirc system. If you want to you can disconnect and check them out to make sure they are not clogged. Additionally, those elbow and T connectors for these hoses usually have check valves and sometimes do not open anymore due to dirt. You should have a working diagram which connector blows in or out before deciding to disconnect and open anything with the fuel recirc system.

 

[fmt2bx]

If you look around the fuel pump unit, underneath are short hoses running from cylinder to another. These are hoses for the fuel recirc system. If you want to you can disconnect and check them out to make sure they are not clogged. Additionally, those elbow and T connectors for these hoses usually have check valves and sometimes do not open anymore due to dirt. You should have a working diagram which connector blows in or out before deciding to disconnect and open anything with the fuel recirc system.

Thanks for the info. I haven't messed with the fuel recirc system yet. trying to establish if fuel pump is working well. Can a fuel pump be weak or is it just working or not.
I disconnected the line going to carb from fuel pump and it seems to be working, however I have no idea if this output has enough pressure/ fuel.
How difficult is it to replace the diaphragm?
Thank you.

 

[Jiggz]

If you have not done yet, before delving into replacing things, you might want to install a clear fuel filter between the pump outlet and the carbs' input. It needs to be clear and the main reason is for troubleshooting fuel related problems. With a good working fuel pump, the clear fuel filter will at least maintain 1/2~3/4 full at WOT. If it goes lower than this then it is an indication there is problem with fuel delivery. Fram G2 from Walmart costs less than $5 and even comes with hose clamps.

 

[Frank Acampora]

Replacing a diaphragm is easy whether you have the old style Chrysler pump or the Mercury square pump. The Mercury pump kit comes with new check valves. The force does not. If you wish to change check valves, and most times they will not need to be replaced, you must buy them.

If you never replaced a diaphragm before allow 1/2 to 3/4 hour. Once you have done it 15 minutes is all it takes.

 

[fmt2bx]

If you have not done yet, before delving into replacing things, you might want to install a clear fuel filter between the pump outlet and the carbs' input. It needs to be clear and the main reason is for troubleshooting fuel related problems. With a good working fuel pump, the clear fuel filter will at least maintain 1/2~3/4 full at WOT. If it goes lower than this then it is an indication there is problem with fuel delivery. Fram G2 from Walmart costs less than $5 and even comes with hose clamps.

I got the boat 2 weeks ago, at first it ran perfectly, then the 3rd time we used it, it started to act up, rough at times, stall, and sometimes just fine. I suspected some fuel delivery problem, I replaced the carb bowl gaskets, check the fuel lines, fuel vent, replaced the fuel line from tank to engine. Replaced the primer bulb. Check the engine fuel filter, replaced the spark plugs, water pump impeller. Now surely, I thought that I had eliminated fuel delivery issues to the motor as well as cooling of motor. Well, it worked ok for ONE day then it started all over gain, this time it purely quit in middle of the lake and impossible to start, nothing, dead!!!!
Got back home and there was no fuel in carbs. After spending an hour troubleshooting, it turn out that the quick fuel disconnect fitting was simply not allowing fuel to go through. In fact, it was more like working or not depending on how it was sitting was male connector.

I really like the idea of having a clear fuel filter not only for filtering but also to see the fuel in the line as you mentioned. Thank you!

BTW: Other problem I had was cold start, it just wouldn't start, looked like the choke wasn't closing the carb enough. Turn out nothing wrong with the solenoid, in fact it was one of the fuel line clamp at the lower carb that was in the way!!! My mistake of course. I had removed the line to inspect it the day before!!!

It is a very steep learning curve, but so far it is still enjoyable and basically there wasn't ever anything wrong with the engine from the beginning.

 

[fmt2bx]

Replacing a diaphragm is easy whether you have the old style Chrysler pump or the Mercury square pump. The Mercury pump kit comes with new check valves. The force does not. If you wish to change check valves, and most times they will not need to be replaced, you must buy them.

If you never replaced a diaphragm before allow 1/2 to 3/4 hour. Once you have done it 15 minutes is all it takes.

Thank you. I have the old style not the square pump. Is it a preventive maintenance item ( if so what interval) or just replace when not working?
Thanks again.

 

[Jiggz]

I wouldn't call the fuel diaphragm a preventive maintenance item but instead more of a corrective maintenance only after a diagnosis points to it. After installing the clear fuel filter, it should give you a better idea if the fuel pump is the source of your problem. As for cold starting make sure you always do the three MUST steps before starting it. Prime, Fast idle and then choke. Normally, the engine will start in one or two tries. After the 2nd try and it still does not start, do not engage the choke anymore as this can flood the carbs.

 

[fmt2bx]

After changing the fuel quick disconnect, no more issues!!! Went to lake this pm with my daughter and the motor ran fabulously, very smooth at all rpm. Good for piece of mind.
Thank you ally
Cheers
Fmt

 

[Jiggz]

Great. So the fuel starvation and air-leak in the fuel system is caused by a faulty quick disconnect. Outstanding troubleshooting.