'96 Mercury/Force 75HP 3 cyl 2 stroke won't throttle up in gear without stalling...

[wolverine9827]

Hi all,

I'm having an issue with my 96 Mercury/Force 75HP 3 cyl 2 stroke..... it starts fine and idles fine, and seems to throttle up ok while hooked up to the water intake and in neutral (though it sounds a little rough)... the problem is when I'm out in the water.. if I throttle it up too much, it starts to sound weird (can feel vibrations and it sounds almost like it's misfiring) and then stalls... I can puttz around all day with no problem... I have replaced the spark plugs and wires and remixed a new fuel batch with sta-bil = no change... being a complete newb with engines and that sort of thing, I'm hoping for some direction from others that know more (which is pretty much everyone!)

I don't have a fuel/water separator - should I get one? Where is this usually installed?
How do you clean the carburetors?
How often should the inline fuel filter be replaced?

Any other ideas?

I appreciate any help....

Thanks

 

[Robert D]

Re: '96 Mercury/Force 75HP 3 cyl 2 stroke won't throttle up in gear without stalling.

The idle speed....and mixture...need to be adjusted while at an idle in forward gear, in the water. This means taking the cowling off, backing it down the ramp, (Still attached to trailer) and then make adjustments after it is fully warmed up.

Okay.....if it dies when putting it in forward gear, often that is from too lean a setting on the mixture. (Or too low an idle speed as well.)

However....if I read correctly, it's at higher rpms it starts to vibrate a little and stalls....that sounds like fuel starvation. Change that filter you mentioned. Get a fuel pump diaphram rebuild kit. Those are normal maintenance items you might as well take care of now. If that cures it, great. If not, check the float level and needle/seats in the carbs. (Pick up a shop manual to refer to for specs.)

How often should the inline fuel filter be replaced? Depends how much you use it. I change mine every year. If I used the boat every weekend year round, I'd change it every 2 to 3 months maybe.

How do you clean the carburetors? Take them off, disassemble and clean... all parts & passages; Use compressed air to blow through everything; Install new needle and seat, and gasket.

I don't have a fuel/water separator - should I get one? Depends. With a built in fuel tank, I would. Using a portable fuel tank, not so important as long as you trust your fuel source. (I have received a dose of water from a reputable gas station before.....) The question is: Do you want to find out about it when you're 15 miles off shore? Or on a flowing river with a kicker motor for backup using the same fuel supply?

 

[wolverine9827]

Re: '96 Mercury/Force 75HP 3 cyl 2 stroke won't throttle up in gear without stalling.

The idle speed....and mixture...need to be adjusted while at an idle in forward gear, in the water. This means taking the cowling off, backing it down the ramp, (Still attached to trailer) and then make adjustments after it is fully warmed up.

Okay.....if it dies when putting it in forward gear, often that is from too lean a setting on the mixture. (Or too low an idle speed as well.)

However....if I read correctly, it's at higher rpms it starts to vibrate a little and stalls....that sounds like fuel starvation. Change that filter you mentioned. Get a fuel pump diaphram rebuild kit. Those are normal maintenance items you might as well take care of now. If that cures it, great. If not, check the float level and needle/seats in the carbs. (Pick up a shop manual to refer to for specs.)

How often should the inline fuel filter be replaced? Depends how much you use it. I change mine every year. If I used the boat every weekend year round, I'd change it every 2 to 3 months maybe.

How do you clean the carburetors? Take them off, disassemble and clean... all parts & passages; Use compressed air to blow through everything; Install new needle and seat, and gasket.

I don't have a fuel/water separator - should I get one? Depends. With a built in fuel tank, I would. Using a portable fuel tank, not so important as long as you trust your fuel source. (I have received a dose of water from a reputable gas station before.....) The question is: Do you want to find out about it when you're 15 miles off shore? Or on a flowing river with a kicker motor for backup using the same fuel supply?

Thanks for the excellent info!! I really appreciate it. The motor seems to operate just fine when it's on muffs (though it's a little rough when throttling up in neutral but no vibrations or anything - just seems to growl/roar with a bit of a 'hey dude, let's not get me screaming unless you have me in the water' type of scariness (if that even makes any sense - it doesn't cough or sputter or anything, it just starts to sound scary loud with a hair of roughness (timing?) and that's only at 1/2 to 2/3 Full throttle - I wimp out from WOT on muffs in neutral fearing that I might damage something - this thing goes into full ROAR at only 1/2 throttle!)

Out on the water, it starts fairly easily with only one push of the choke/primer and idles great. I can shift into forward or reverse and it continues to idle just fine. I can then slowly throttle up to maneuver in either forward or reverse without any problems or vibrations and can continue at this speed indefinitely (around a 2-3 mph puttz) It's when I attempt to throttle up from there to get past 5mph that I start to feel vibrations and can hear the pitch of the motor change (like it's coughing) and either I have to quickly throttle back to puttz speed or it will stall. Once it stalls it won't start for a few minutes and once it does, the first few times it starts, it struggles to stay running and dies after a few seconds but runs stronger and longer each time. Once it stays running, I'm back to square one where I can idle and low throttle puttz around all day.

I'll look into the fuel pump rebuild kit and also attempt to adjust mixture next time we're out... it's still fun to puttz around all the dolphins here

Once again, I greatly appreciate your expertise!

 

[celtic gelf]

Re: '96 Mercury/Force 75HP 3 cyl 2 stroke won't throttle up in gear without stalling.

do you run straight gas or some ethanol mix....I was told not to run ethanol gas in a two stroke...plus he told me to run premium, mix it in a portable tank and fill the boat which has a fixed tank...this completely mixes oil and gas and mixes it once again as I fill my boat...how'd did he put it???? for the few bucks more for better gas you'll get better performance and what's the cost of a powerhead??? is it worth the premium and double mixing....I'd say it made sense to me as it was explained..