One more question 3 cyl 90 Merc carburetors

I got my linkage parts in yesterday and installed them. Then I went through the linkage setup per the manual and in hindsight it looks like I got it all per the book.

The interesting part of the experience was that in the linkage section it mentioned setting the carbs at a certain place and then go over to the specifications and do a carb low speed jet adjustment.

That's when I found that I am supposed to have #1 at 1/2 turn and the other 2 at 1 1/4 turn. Well, when I started my fiasco a week ago they were all 3 set to 1 1/2.

After I made the adjustment, with the idle set by the correct timing (5 degr before) the idle settled down and the engine ran (on muffs) really nice.

So, apparently some of the explosion problems I had were caused by too much fuel in the mix on #1 and apparently this fuel would collect in one of the other cylinders and periodically explode.

Soooooo how is it that #1 is adjusted so lean? Don't I need some fuel/oil in the cylinder to keep it lubricated?

Thanks,

Mark

Re: One more question 3 cyl 90 Merc carburetors

Well, as luck would have it, I solved my own problem. My manual was for engines earlier than mine and the numbers I put in the thread actually were for a '95 engine even though the manual was through later year '90's engines. Mine is an '02.

Worrying about the over lean #1 caused me to go online and subscribe to Solco online service manuals and in there I almost immediately got a lot of info that my Merc service manual didn't dwell into for my particular engine. I know iboats sells their manuals for about $10 less, but this manual was engine specific and fabulous rather than covering A-Z engines for a span of years.

Following their instructions and some tips I picked up on here about how much to change the mixture screw at a time, I think I wound up with a workable solution. Engine runs fine, did it per the manual so no mavericks here, carbs are adjusted almost identical and restarts in a heart beat.

Nowwwwwwww if we can get some water in these Texas lakes, I can take it out to verify my work.

Hope this helps someone......

Mark

Re: One more question 3 cyl 90 Merc carburetors

Were you running the motor on the hose or submerged, as final idle mixture must be done while ON the water and IN Forward gear. The addition of water in the exhaust passage of the mid-section increases fuel requirement as does the load on the motor being in gear turning the prop.

Once in the water, readjust all idle mixture screws to BEST idle, THEN almost an additional 1/8 turn out (CCW) to provide even more additional fuel for crisp acceleration.

Test hole shot acceleration, any hesitation, even the slightest, indicates a need for additional idle fuel. Make very small changes, repeating acceleration tests until perfection.

Note, an increasing load such as a couple of full cooler, additional large passenger, or pulling a skier can also increase idle fuel requirement for crisp acceleration.

Re: One more question 3 cyl 90 Merc carburetors

CharlieB said:

Were you running the motor on the hose or submerged, as final idle mixture must be done while ON the water and IN Forward gear. The addition of water in the exhaust passage of the mid-section increases fuel requirement as does the load on the motor being in gear turning the prop.

Once in the water, readjust all idle mixture screws to BEST idle, THEN almost an additional 1/8 turn out (CCW) to provide even more additional fuel for crisp acceleration.

Test hole shot acceleration, any hesitation, even the slightest, indicates a need for additional idle fuel. Make very small changes, repeating acceleration tests until perfection.

Note, an increasing load such as a couple of full cooler, additional large passenger, or pulling a skier can also increase idle fuel requirement for crisp acceleration.

Click to expand...

Thanks Charlie. Will do. I will see how things go. On muffs I am currently running about 1000-1100. I expect that to drop on the water; how much we'll see. Manual says if F in water at idle should be 675. On my boat, doing a water adjustment will be a real chore to get-r-done and not fall off the stern. Obviously it will take 2 to get the job done....I want someone at the helm when I'm back there.

Mark

Re: One more question 3 cyl 90 Merc carburetors

I've often backed a boat to the dock and tied off both rear cleats using good line, then sat on the edge of the dock listening, feeling, tweaking adjustments, til I was ready to hit the throttle, then get on boat and smack it just hard enough to know if it was going to pull or hesitate. Once finally ready, untie, idle out and hit it.

Re: One more question 3 cyl 90 Merc carburetors

CharlieB said:

I've often backed a boat to the dock and tied off both rear cleats using good line, then sat on the edge of the dock listening, feeling, tweaking adjustments, til I was ready to hit the throttle, then get on boat and smack it just hard enough to know if it was going to pull or hesitate. Once finally ready, untie, idle out and hit it.

Click to expand...

Now that's a much better idea. I usually boat on a 1000 acre lake during the week when there aren't but half a dozen trailers in the parking lot. There are 2 ramps each having 2 slots. I could do it and not be a bother to anyone.

Thanks,

Mark