rough idle and cuts out when put in gear 75hp mercury force

[CharlestonFF]

I just bought a boat and have been working on the motor trying to get it to run better. The bulb used to go soft until I replaced all fuel lines except main line from gas tank to bulb. The motor is running a little bit better except for when you go to put it in gear the engine dies due to the rough idling. Could the timing be off? The guy I bought it from adjusted what I think is the timing thinking it was the idle. If timing is off how do you sync with the gun. Also when the motor is on the hose it runs great put it in the water the back pressure I am assuming is causing it to choke up.. I dunno starting to run out of ideas.Any suggestions would help!!!

Thanks for your time

 

[pnwboat]

Re: rough idle and cuts out when put in gear 75hp mercury force

The first thing that you want to check is the compression. Low compression can cause a variety of symptoms that cannot be "adjusted" out.

 

[CharlestonFF]

Re: rough idle and cuts out when put in gear 75hp mercury force

I checked the compression when I bought the boat last week. The compression is 130-135-130. When test driving it the boat ran well except when we were bringing the boat back to the dock it died as if the idle was set to low. When we got back to the house I think he mistakenly adjusted the timing screw rather than the idle screw. Any idea what the idling RPMs should be and how I could re adjust the timing?
Thanks for your Help

 

[pnwboat]

Re: rough idle and cuts out when put in gear 75hp mercury force

Here is a video that goes through the steps of setting the timing. The guy in the video says to set the timing to 28? BTDC. Your motor should be set to 30? BTDC.

How to set timing on outboard motor - YouTube

Might be a good idea to check the fuel pump diaphragm, and while you're at it, the water pump impeller. If either of these fails, it's a show stopper. If the water pump impeller fails, there's also a possibility of doing engine damage. I always change these two items when I get a used motor.

Not sure if your 75HP has a single or triple carbs. Depends on the year. If you have triple carbs, then you should do a "Link and Sync" Frank A from the Force Forums has a good video on this subject.

carb and timing tutorial - YouTube

Make sure the idle mixture screw(s) are set correctly. Initial setting should be one turn out from lightly seated. Typical final setting is 1 to 1 1/4 turns out from lightly seated.

Idle speed with the motor out of the water on muffs should be around 900 - 1000 RPMs. Idle speed in the water should be around 750 - 900.

Idle speed is set with this screw (Red Arrow) that has a locknut to keep it from moving. The Yellow Arrow is the timing adjustment.

 

[CharlestonFF]

Re: rough idle and cuts out when put in gear 75hp mercury force

So the timing was adjusted instead of the idle screw! I hope that explains my issue! The year and model of my engine only as a single carb in the center of the engine! Thank you for this information! Would this tutorial help me if I only have one carb?

 

[Jiggz]

Re: rough idle and cuts out when put in gear 75hp mercury force

Yes, the process is still the same in setting the timing and also with the setting of the idle mixture screw. Even the synch and link tutorial will help albeit you only need to verify one carb instead of three. You might want to reset the timing first and then set the idle rpm. From there it's only a matter of fine tuning the carb with the idle mixture screw.