Force 125 coughing from through the exhaust?

[cg3]

I have a 1989 Force 125 ob. It starts up fine but as soon as it warms up it begins to cough through the exhaust repeatably. Any thoughts or comments about where to start would be greatly appreciated. I tried to attach a cell phone video of the motor running but it would not attach. Thanks in advance.

 

[Jiggz]

You need to find out if it is a misfire, backfire or cough (?) as you describe. Let it ran for a little bit and then check the spark plugs to see if they are fouled or if they are shiny clean. A normal firing spark plug will have light to dark tan discoloration in the middle. If all plugs look normal, try checking the timing and also do a de-carboning of the motor.

 

[jerryjerry05]

Coughing at idle, could be the air screw needs adjusting?
Start at about 1 and 1/8th out from lightly seated.
Then motor warm adjust from there.
Also do a compression test.
Any fuel coming back through the carb? Check the reeds.

 

[Frank Acampora]

This could also be a clogged oil recirculation system. Remove the two plates on the electronics side of the engine held on with four bolts each and clean the passages. If there are screens, clean them too.

 

[cg3]

You need to find out if it is a misfire, backfire or cough (?) as you describe. Let it ran for a little bit and then check the spark plugs to see if they are fouled or if they are shiny clean. A normal firing spark plug will have light to dark tan discoloration in the middle. If all plugs look normal, try checking the timing and also do a de-carboning of the motor.

Jiggz it is definitely more of a cough than anything else. It actually sounds like an old hit and miss motor that has that pressurized cough sound. At any rate, I attempted to do the obvious first and look at the plugs, all were wet and black. I then decided to try adjusting the carb at which point I found the lower carb mixture screw was only a 1/4 turn out and the upper was about 1-1/8. I adjusted both to approx 1 to 1-1/2 turns, messed with the idle a bit and the timing and all seems well. It even fires up way faster now. I have been quite busy so I have not had a chance to pull the plugs again or get it out on the lake yet but with the ear muffs on it is ten times better already. De-carboning will be next for assurance. Thank you for your advise once again, I appreciate it.

 

[cg3]

Coughing at idle, could be the air screw needs adjusting?
Start at about 1 and 1/8th out from lightly seated.
Then motor warm adjust from there.
Also do a compression test.
Any fuel coming back through the carb? Check the reeds.

jerryjerry05, I looked at the plugs, all were wet and black. I then decided to try adjusting the carb at which point I found the lower carb mixture screw was only a 1/4 turn out and the upper was about 1-1/8. (Great call) I adjusted both to approx 1 to 1-1/2 turns, messed with the idle a bit and the timing and all seems well. It even fires up way faster now. The only time I see fuel coming back through the carbs is when I first choke it and that is it. Didn't do a compression test because I don't have the tool and I do not know how to check the reeds as of yet, still on my list to learn. Thank you for your advise, I really appreciate it.

 

[cg3]

This could also be a clogged oil recirculation system. Remove the two plates on the electronics side of the engine held on with four bolts each and clean the passages. If there are screens, clean them too.

Frank, I opted to check the plugs and all were black and wet so I adjusted the mixture screws, played with the idle and the timing and all seems well now. If I have more problems when I get it on the lake then your suggestion of inspecting the oil recirculation system will be next on the list along with a compression test and a reed inspection. Thanks for your suggestion, I really appreciate it.

 

[cg3]

Just wondering, can an idle mixture screw somehow run itself in? I would think maybe it could back out with the vibration and the spring tension if anything but not run inwards. I find it strange that I have owned this boat as long as I have and it was running with the lower carb screw only about a 1/4 turn out and I did not touch the carb adjustments?
Thanks

 

[jerryjerry05]

It's absolutely AMAZING what you find with someone else's motors.
It's also amazing that some motors actually run the way they are set up.
The air screws only affect slow speed operation.
The old owner probably said it runs great at top speed so the heck with it.
Some people shouldn't pick up a tool of any kind.
So feel good that he wasn't messing with anything!!

If the carbs not spitting fuel other than when you choke it. Don't worry too much with the reeds, they are behind the carbs and seem to be OK.
If it's running good and not missing the comp is probably good.

 

[Jiggz]

I have very serious doubts an idle mixture screw can vibrate loose and open and close itself, as long as there is that proper sized and tensioned spring.

 

[cg3]

Jiggz, Frank, Jerry or anyone, I have been looking for the post that many people said they have found on here about replacing a single piston on a 89 Force 125 ob but I can not find it. Maybe I am wording it wrong but it is certainly not coming up. Can you direct me to the post that goes into great detail about how to do this by chance? Any help is greatly appreciated.

 

[Jiggz]

Unfortunately, since the "Forum upgrade" important things that you can do before are not available anymore. The search functions for some reasons is nowhere to be found. Even with manual searches, the old posted pics are nowhere to be seen. Sure there is a link of some icon about an attached pic but clicking it just gives you a blank white screen. Maybe one of these days, a forum member will create a word document describing all the steps and attaching pics at the same time on how to replace a piston, including refurbishing the cylinder.