1990 yamaha 200 hp overheats at high rpm

[RJF]

My 200 yamaha overheats at over 4200 rpms I have changed thermostats prv valve which did help water pressure and water pump.When I changed the t stats and prv valve looking into the motor I did not see much build up of corrosion but i'm not counting out aproblem with the water jackets yet but what i could see looked pretty good.Now my question is it possible with the e10 gas I did have problems with my fuel filter water seperator clogging used 8 filters this year could the jets in the carbs be clogged causing alean condition makeing the motor overheat? when I do get a alarm iback off to idle and the motor cools alarm stops in less than 1 min then i can run at 4000 rpm all day long no problems.Any help or suggestions would be appreciated. Thanks Ron

[slim]

your problem is that the water jackets are corroded. remove the heads and water jackets and beadblast them. thats the only way to get them clean. repaint inside with green zinc chromate.

[RJF]

Thanks slim for your reply I will pull th heads this week and check them out .Thanks again Ron

[Ken]

Ron,
What pressure are you getting out of your water pump ?
Assuming your pressure control valve is ok, you should be getting around 5 psi at idle and 20+ above 4000 rpm.
If it has been at least three years since last water pump repair, then your pump may be weak.
Also, you need to pull the thermo switches and test them in a pan of heated water - you should be able to measure continuity between the two wires (contact closure) at around 180 degrees f.
I have personally experienced one closing at 130 degrees, giving me a false overheat condition.
Good luck - and let is know what you find [img]smile.gif[/img] ,
Ken K

[RJF]

cleaned the heads and water jackets also found 2 hole in the head gaskets one in each gasket.The motor runs better than ever I gained 100 rpm at wot. Thanks again Slim and Ken for your help.

[Blair]

RJF great to hear. Did you paint the mating surface on the head or left that clean ie: bare metal where the head gaskets actually seals?

I'm about to paint my ex plates and head and head cover. Just wanting an idea if what not to get paint on.

I intend to install old spark plugs to keep threads clean and cover the combustion chambers only.

???

Cheers

[slim]

what i used to do is paint it and go back after it dried with a razor scraper and just knock the paint off. it should come off really easy. i didnt mention this before but you need to get a sanding block(dont do it with your hands) with some 80 grit paper and sand the gasket surfaces to get a good shiny uniform look. your not really trying to get it looking new, just better then what it is. try not to sand to much in one place either. if you do this, the paint should scrape off very easy.