rich/lean yam 90/90hp

[Lew Taylor]

what is the correct settings for my triple carb 90 ,ie how many turns out for mixture screw.
It has been sujested that the overheating at high revs could be due to the carbs running to leans Regards Lew

[Ken]

Lew,
The mixture screw you refer to is the pilot screw adjustment for the idle mixture - I do not believe it effects the mid range or high speed mixture at all. I don't have the manual for your motor, but the adjustment is gonna be about 3/4-1 turn out. Someone will chime in and tell you exactly.
Are you having overheat problems? The pilot screw adjustment won't cause you overheating at high speed - the mixture at midrange/high speed is fixed. Now, the low and high speed jets being clogged up with gum and varnish could cause you to run lean. Has the motor been allowed to set up for, say, six weeks or more w/o being run? Is your motor running smooth thru out the rpm range?Your carbs may be clogged up. If you suspect that, then I would recommend a shock treatment with SeaFoam or RingFree, pull the jets and squirt carb cleaner into the orifices. Maybe a carb kit install is in order.
You really need a Yamaha shop manual if your are going to be doing any maintenance yourself.
Good luck [img]smile.gif[/img] ,
Ken K

[Hamfisted]

The most common culprit is the waterpump impeller being worn out. Unable to pump the water volume needed at higher rpm conditions. Do you know how old the waterpump is?


Mike

[Lew Taylor]

thank guys new water pump and I have cleaned out the head water ways etc .still over heating water pressure 17psi ,6 at start up.
My dealer has already had 2 goes at fixing the problem, 1,new water pump, new thermostat and popet.and I have fitted PSI gauge stripped head and cleaned out < it was clean any way.
Just thought it might be carb related will check carbs regards Lew

[jb123]

overheating/ high revs... might wanna try to lower your motor a notch,ensuring waterflow to pump and allowing full prop grab.i like to keep them as high as possible until it impedes performance.

[Lew Taylor]

interesting angle ,will try it out in the weekend,I have a hydro fin fitted to cav plate to stop porposing ,never thought to lower the motor ,nore has my dealer
regards lew

[Ken]

Lew,
Let's see - new water pump, new thermostat, new poppit valve, cleaned out the head water jacket, 17 psi of water pressure, and still getting overheat warning. I would pull the thermo switch and test it. I have personally experienced one closing at 130 degrees instead of 180 like they are designed to do. Just heat in a pan of water and use a thermometer and ohm meter and monitor contact closure. Should close at 180 and re-open at 160.
Good luck [img]smile.gif[/img] ,
Ken K

[Lew Taylor]

thanks ken will test tonite ,had it replaced when i purchased the boat year last but it would put my mind at rest ,also the dealer tested it and said it was alright.

[Bazooka Joe]

Could you back up a step tell us a bit more about the symptoms? Meaning- When did it start overheating, how long has it been happening, how far do you run before it happens, does the powerhead feel hot, how old is the powerhead, fresh/old fuel, sparkplugs & piston tops look like what, etc.?

As to the fuel screws, I have mine about 1.5 turns out on all three cyls. Depending on your boat rigging, yours will likely be different.

[Lew Taylor]

Problem solved I think,Ken the themo sensor worked at 155 amasing the yam dealer has put me throught all this expence and frustration and over $500 nzd many thanks to all who have replied to my emails

[Ken]

Lew,
Are you saying that the thermo switch contacts closed at 155 f.? If so, then that is a bit low.
Ken K

[Lew Taylor]

Yes Ken thats the only thing (thermo sensor)so far I can find that falls outside the what the factory settings should be.( will try the lowering of motor also) may sort out the porposing)
It has been very frusrating ,any way on saturday I plan to take her out and hopefully it will be fine. if not I will be back, so the saying goes
best regards Lew