90 hp 2 stroke idle mixture screws

[Xjclint]

Factory settings have my 2000 2 stroke 90hp 3cyl idle mixture settings at 1 1/4 turns each. Starts and idles but is a little jumpy. Move them in a bit and rpms come up and it smoothes out a little bit i worry about being too lean. Move them out past 2 and it bogs and dies.

How lean can you go with the screws before you worry? Is less than 1 1/4 an issue?

 

[Texasmark]

Manual say to get the engine warmed up and get out in smooth, open water. Firewall the throttle. Open till boat will take throttle and get you on plane without stumbling....all should be about the same opening.

 

[roscoe]

A little bit of a bog or hesitation is a good thing, as long as she kicks in and goes a half second later.

I would not be running them leaner than 1.25 turns, more like 1.75 turns out.

 

[Texasmark]

A little bit of a bog or hesitation is a good thing, as long as she kicks in and goes a half second later.

I would not be running them leaner than 1.25 turns, more like 1.75 turns out.

I'm just quoting the Mercury service manual. I never had a problem with my 90 on my 17 ½ Fishmaster alum, BB running a Ballistic SS 24XL....picture in my Avatar. Had it setup like the manual states. Sometimes I'd push the trim out past vertical and hammer down on it and it just loved it....about 3 hops getting going and it was gone. Can't believe that boat was BIA rated for a 135 hp.

 

[Xjclint]

So here’s the strange thing, the boat won’t idle with the plates all closed and the screws at 1.25 turns. I tried 1 turn to 2 turns and it just bogs. Fuel pump is good, spark plugs are new, but compression is 120,120,90 (known issue due to a clogged oil line — running it until it dies and Repower). Not willing to break apart the block so what’s the best way to get it idling for now?

Should I open the bad cylinder plate a little at idle or should I try to keep them all the same but open them a tad? Or should I tweak that idle mixture screw super rich until it runs (assuming it has more air now due to compression issue)? Can get it to idle ok by keeping that one open a little more but trying to come up with the best way.

 

[Texasmark]

You are basically running on 2 cylinders and in the driveway on muffs, sounds fine. Put a load on it and it falls on it's face. Like it or not, I doubt you will get there from here! The manuals states, below 120 expect problems. You are a long way south of 120!

 

[Xjclint]

Just an update for those with similar issues. Open one throttle plate a little at idle (the lower cylinder) and it runs fine. Idles at 1200 but starts every time and runs prefect above idle. Compression has stayed the same after about 150 hours so far so decent fix until it decides to quit.

 

[Texasmark]

Glad you got a 0 cost fix. On idling at 1200, only negative aspect is wear and tear on the LU when shifting. Crunching noises when shifting are wearing out your shift clutch dog and engagement mates on the rear of the F and R gears....R especially since it's vertical sided cogs and slots.