90 hp Carb idle adjustments.

[99scout1976]

Hello all I?m back again unfortunately ...
I have a 1999 two stroke 90 hp runs fine on the hose but out on the water must be started in the high idle position and will only idle in Neutral for two to three mins before stalling. When shifted to forward gear often will stall and seems to bog down before getting to WOT but once there runs great. As for reverse gear it bogs down as if it has too much fuel then dies almost every time. I have cleaned the carbs ran mercury power tune threw it and added sea foam. I am confident that I need to adjust idle settings or at least hopeful that?s all it is yet am unable to find anywhere on how to do so for my motor. I have a "'main'' idle screw and then one on each of the three carbs. It is my understanding and please correct me if wrong that the top carb is adjusted for low/idle speed, bottom for high speed and I have no idea and have not found anything on the middle carb. If anyone could please educate me on these adjustments or have any other advice I would be forever grateful. Thank you.

 

[jerryjerry05]

Re: 90 hp Carb idle adjustments.

Need serial#s.The three carbs are are all basically the same.The air screw is set on each one.
Top and bottom,no idle or slow idle or high idle set individual.
That will cause you to burn up the motor if you start messing with screws.
If I'm thinking about the right carb the air screw is on the side is the only adjustment on the carb itself.Start at 1 turn out and adjust from there.
The idle is set on the side of the motor through the linkage and a couple of screws.Again a FACTORY manual is needed.Seloc and Clymer DON"T cover the motors right.
I sent U a PM.J
Get a FACTORY manual and read.

 

[Texasmark]

Re: 90 hp Carb idle adjustments.

I just finished the procedure on my '02 90 triple which is basically the same critter. Charlie B directed me as to how to set it up on muffs and then how to tweak it in the water. If you look back a few days at a post of mine with the title something like "Ok guys here come the credits" I iterated the process Charlie B gave me, thanking him and others for their help and commented on what I had to do and the results.

In short, get your best operation on muffs and go to the water and back your boat in just as you were going to launch it but leave the winch rope/cable attached. Back off (unscrew) the low speed idle screws the width of the tip of your screwdriver at a time on all 3 carbs till you can idle and when put into gear, the engine will take the load and try to push your trailer/tow vehicle up the ramp. Then you are good to go.....worked great for me with only 2 screwdriver blade with adjustments.......that's like 1/32" of a turn sorta....not much....these carbs are really sensitive. The manual says that once you get them set up "leave them alone". "Not designed for minor engine tweaking"....and I believe them.

The manual indicates that idle rpm is 675 in the water in F gear boat in motion (not on trailer). Timing is 5 BTDC idle and 22 at WOT with a timing light cranking the engine. The idle set screw tweaks timing.

I set my timing per the manual then went back to the carbs and tweaked them till I got my rpm's down to about 1100 on muffs in N. After going to the water and doing the trailer adjustment, my idle was higher than the book numbers under the same conditions, but I would rather have it that way and I have a rubber hub prop which absorbs the impact of a little more rpm's when shifting. I got into my mess last summer when in the 100 degree heat we had caused my engine to quit while idling. I thought I'd just open my carbs 1/4 turn and that would be that..........well let me tell you sir, that tain't the way this engine wants it and it really showed me it's dislike of having done that.

HTH,

Mark

 

[CharlieB]

Re: 90 hp Carb idle adjustments.

.............. I have a "'main'' idle screw and then one on each of the three carbs. .........................

That 'main' idle screw on the timing lever adjust overall idle speed by changing the idle timing.

The idle mixture screw on each carb adjusts idle mixture. Initial setting spelled out in the manual calls for 1 and a half turns out from 'lightly' seated. This should provide enough fuel to get the motor started. From there, adjust each carb to achieve 'Best' idle speed IN the water and IN forward gear, Then further open each idle mixture screw about 1/8 turn to provide the additional fuel necessary for crisp acceleration.

Test acceleration, ANY hesitation, even the slightest, indicates a need for more idle mixture, make small adjustment, repeat testing to perfection.

Final idle speed adjustment with the 'main' idle speed screw is then finished, again, while IN gear on the water.

 

[Texasmark]

Re: 90 hp Carb idle adjustments.

Then further open each idle mixture screw about 1/8 turn to provide the additional fuel necessary for crisp acceleration.

Charlie, this is not the right answer. Just randomly opening the low speed screws is where I got into trouble in the first place.

Per your instructions, put it on the trailer and open the low speed jets 1 screwdriver width at a time, after you did the best you could on the muffs, until it can "attempt" to push the trailer and tow vehicle up the ramp....then you are good to go........yessssss. This is the right answer. Forget the additional openings on this engine.

Mark

 

[99scout1976]

Re: 90 hp Carb idle adjustments.

CharlieB, Mark,
CharlieB, is there anything else I need to do with the ''main'' idle screw if it controls the timing?
Mark, Low speed jets? You are talking about the idle mixture screw on each carb correct? Are you saying that I should only adjust idle screws on the crabs and not the ''main'' idle screw?
It sounds like you guys are saying the same thing ... only mark your saying I should not further open the 1/8 for the additional fuel for crisp acceleration?
So as I understand it my plan of action is to take it straight to the water since I have it running well on the muffs and with the boat still on the trailer start the motor put in forward gear and adjust the idle screws on each of the carbs until it pushes the trailer and tow vehicle after I gently seat the idle screws and back them out 1 and 1/2 turn?

Again thank you for your patience with my ignorance and your help.

 

[99scout1976]

Re: 90 hp Carb idle adjustments.

An update,,, so from reading threw the forums I saw a post about cylinders not firing and made me think back to spray power tune into the carbs. I remember that when I sprayed my bottom carb there was no response from the motor like there was on the top two. Could this mean my bottom cylinder is not firing? Would this be the reason for my motor not idling? If so what would be my next step to correct this problem?
Again Thanks!

 

[CharlieB]

Re: 90 hp Carb idle adjustments.

First step would have been a compression test AND a spark test.

Without compression and adequate spark to ignite the fire, fuel won't do any good.

 

[99scout1976]

Re: 90 hp Carb idle adjustments.

Did a compression test and all three cylinders are good. Going to do spark test tomorrow afternoon after i wake up. I got hit with Staff Duty tonight and don't get off till 0900 UGH. I will let you guys know how it goes. Thanks!

 

[99scout1976]

Re: 90 hp Carb idle adjustments.

Ok so I did the spark test and it was good. I even unplugged the two other plugs and started it just fine on the bottom cylinder that i thought might not be getting spark. So unless these plugs can still spark while unplugged they are all good. So I guess it?s to the boat ramp tomorrow to adjust idle speed. I would like to add that after running on the hose today doing the test there was a very thick black almost looked like oil coming out of the exhaust. I am hoping this is just the remainder of whatever carbon that still in the motor burning out. Any thoughts on this would be appreciated.
Thanks, Jason

 

[99scout1976]

Re: 90 hp Carb idle adjustments.

Took my boat down to the lake today and did a very MINOR adjustment on the carb idle screws and it made a world of difference! Boat is running great! Thanks for all of your help!