1999 Force/Merc 75HP 3 Cylinder 2-Stoke Rough Running Issues

[pshelfo]

Follow up question on the welch plug. If i remove and clean do i have to take the bowl off again or just remove the welch plug, clean amd reinstall? Took the boat this week and it ran good for the first time. Started okay, idle was fine, top end was fine. Only remaining issue is the rough run at around 2k rpm. A couple of times stalled out when putting in gear and waiting to throttle down. Is the welch plug still recommended?

 

[Chris1956]

Just so you know, 2000RPM is about where the idle jets stop providing any significant fuel, and the mains take over completely.

If it were me, I would pull the bowl off and clean the emulsion tube from below, and hopefully that will get the passages under the welch plug. I have not worked on that type of carb before, so you would need to look to see if that is possible. If you do remove the welch plugs, you should disassemble the carb completely as dirt can move around as you clean the carb.

On a positive note, it sounds like you are close in carb tuning. Double check the float height adjustment, throttle synchronization, timing and make sure the main jet and its passages are clean, and that is about all you can do.

 

[Faztbullet]

Its a Force with Merc lower and ignition..

 

[jerryjerry05]

That motor is still mostly FORCE. Might have some MERCURY parts(ignition) but still mostly Force.
The stalling and puff of smoke makes me believe the 3 port cover gaskets are damaged and sucking air and causing the poor running and smoke etc.
If you can get it running? spray starting fluid around the intake side of the block. Spray around the port cover and carb bases and anywhere on the intake side. If spraying makes a difference in the way it runs?? then it's sucking air.

































iostly force

 

[pshelfo]

I have some better news after messing with things a bit more. I ordered the Berryman carb dip carb cleaner and soaked the carbs for a couple of hours and made sure cleaned and sprayed all jets and holes. Re-installed, set fuel mixture screws 1 1/4 and got back out on the lake. Motor did not like 1 1/4 out as I was having stall in low idle. I moved to 1 1/2 out on all three carbs but it seemed like I was running rich but was not stalling. I have it now set to 1 1/3 out and am at pretty good place. The boat idles great, runs WOT with no issue and for the most part does not stale out. Doing a better job at my choke procedure the last two times and the motor started up on the first crank which is great.

The only things I see are when revving in idle it is still not smooth (but not sure it has ever been) it seems like I have more smoke then it should upon starting up (not an issue when WOT). When I stop to fish (hour or so), come back to start, I have to rev it in idle a bit as when you put in gear sometimes it wants to stall until you get it going then all is fine. It is like it needs to warm up.

Is there a procedure to fine tune the fuel mixture across three cards as I tried what is written in posts (turn down till motor stalls and then back out) but that does not seem to work. Or perhaps an exact setting for this motor where not all carbs are supposed to be set the same way?

 

[QBhoy]

I have some better news after messing with things a bit more. I ordered the Berryman carb dip carb cleaner and soaked the carbs for a couple of hours and made sure cleaned and sprayed all jets and holes. Re-installed, set fuel mixture screws 1 1/4 and got back out on the lake. Motor did not like 1 1/4 out as I was having stall in low idle. I moved to 1 1/2 out on all three carbs but it seemed like I was running rich but was not stalling. I have it now set to 1 1/3 out and am at pretty good place. The boat idles great, runs WOT with no issue and for the most part does not stale out. Doing a better job at my choke procedure the last two times and the motor started up on the first crank which is great.

The only things I see are when revving in idle it is still not smooth (but not sure it has ever been) it seems like I have more smoke then it should upon starting up (not an issue when WOT). When I stop to fish (hour or so), come back to start, I have to rev it in idle a bit as when you put in gear sometimes it wants to stall until you get it going then all is fine. It is like it needs to warm up.

Is there a procedure to fine tune the fuel mixture across three cards as I tried what is written in posts (turn down till motor stalls and then back out) but that does not seem to work. Or perhaps an exact setting for this motor where not all carbs are supposed to be set the same way?

Excellent work, sounds like.
All I might ask or mention, is that it is usually best to set up the carb adjustment when she is absolutely warmed up to operating temps and conditions. If she isn't, then you can end up chasing a never ending sweet spot, only to find that she doesn't run well the next time you fire her up or when she's under load and warmed up.
I'd say that you shouldn't be too far wrong at 1 1/2 turns out for seeing how she goes.
Anyway, not sure if you have been adjusting when cold or on the muffs or otherwise. Thought I would mention it anyway. More than once, I have tried to set up an outboard carb setting, when she's on a trailer or test tank...then I would almost always find that it would need a tinker again, when the engine is under load, warmed up and pushing a boat through the water. Making sure she goes well in gear at idle speed is often a thing to make sure is achieved.

All the best

 

[ct1762@gmail.com]

you may want to test running voltage at each CDM module with a DVA adapter. I would just rule out any issues there since you did so much with fuel. these merc ignitions are very simple as the CDI is built into the ignition coil and can be tested easily. i have the same one... quite rare 3 carb motor. actually its a 90hp with different smaller jets in it. everything else the same.

 

[pshelfo]

So my saga continues. I took a little break on the repair stuff. Went out a couple of weeks ago and could not start the motor right out of the dock. Went off to the side and let it sit (seamed like it was flooded but could not tell). Cranked and cranked about sitting for 15min and then got some life. Started it and rest of the day ran fine. A couple days later put on the hose and it cranked right up first time using the same process. Son took it out of the lake today and used process could not get it to start. Even after sitting for about 30 min nothing. I got it home and tried and could not get it to start. Came out later and had a few burps of life but could not get it crank. Sprayed a little starter fluid and eventually got it to crank over. I ordered a spark gap tester and ran it on all three cylinders and am getting very strong space 1/2 inch out and more. Still don't think it is running running great at lower RPMS as it sputters randomly. Not sure what would cause it to randomly have such issue starting. Don't think it is the CDM going bad as the spark was steady and strong as I revved it up. When the motor burped the spark did not change. The other I sprayed starter fluid around all the carb gasket areas which another post suggested - the motor RPMs did not change. Not sure where to look at this point. Did notice the SOLENOID-Primer dribbles out fuel from the top hose instead of a good squirt. But do here the click each time I push in the key.

 

[ct1762@gmail.com]

does it spark w. plugs in? needs to turn 250rpm or so. full charge on battery. it does sound like you are describing a lean condition though. primer works and throttle plates 100% closed? how many turns out are the slow speed needles?

 

[pshelfo]

Yes it does spark with plugs in - checked that to. Also have a brand new cranking battery with full charge. I have all three idle mixture screws turned out 1 1/3 turns - but maybe that is too lean. I have had a hard time finding the right setting for idle mixture screws for this motor.

 

[pshelfo]

Yes it does spark with plugs in - checked that to. Also have a brand new cranking battery with full charge. I have all three idle mixture screws turned out 1 1/3 turns - but maybe that is too lean. I have had a hard time finding the right setting for idle mixture screws for this motor.

 

[pshelfo]

I am also still getting black/grey exhaust soot on my SS prop which tells me it is still running rough.

 

[Nordin]

You mention you have great spark jumping 1/2 in that is good.
But when you try to start it and it would not start how does the spark plugs look like?
Are they wet or dry?
As this engine has a primer solenoid instead of choke butterflies does the primer work as it should?
The primer has a diaphragm inside and it takes fuel from one carb bowle and squirt it into the crank case just behind the carbs.
Maybe the engine is flooding from the primer if the diaphragm is torn or it does not get any fuel at all when priming.
Check the plugs when hard to start, are they wet or dry.

 

[Faztbullet]

The primer has a diaphragm inside and it takes fuel from one carb bowle and squirt it into the crank case just behind the carbs.

The primer does not have a diaphragm inside, it is a one-way valve. It uses pressure from the primer bulb and fuel pump to squirt fuel into intake when activated

 

[racerone]

Agreed with the above.-----Most electric primers are a valve and are not a pump !

 

[Nordin]

Well, diaphragm or a piston in the primer.
OMC has a piston, Force may have a diaphragm.
I have never pull one a part.
You have to activate and deactivate with the key pushed in.
If it leaks through it the engine will run rich that is one of my suggestion to check for at this issue.

 

[racerone]

The electric primer valve on OMC is not a pump!!-----What looks like a piston is the core of the solenoid.

 

[jerryjerry05]

Pinch off the hose going to the primer after it's started.
Then spray starting fluid around the intake side of the motor, this includes the carb bases and all around the intake side of the motor. If that makes a difference?? Tour sucking air and need a gasket or two.

 

[The Force power]

The electric primer valve on OMC is not a pump!!-----What looks like a piston is the core of the solenoid.

That "core" is called a plunger

 

[racerone]

It is not a pump.