Do 250r's generally run hotter than a bike

[jmack3986]

I was wondering if the 250r just seem to run hotter than a 250 bike. I have been having alot of issues with this and i am just wondering.

[TeamGeek6]

Love the Avitar picture, thats good jumping form, head up, body back.

They overheat from either too much fuel or weak ignition. Since its the same engine as in the bike, no, that doesnt cause it.

Mine used to do that till I rebuilt the ignition system and got a clean, white spark plug, now the pipe goes to 240*F on idle and cylinder goes to about 135*F.
It runs so cold on idle that I had to put a thermostat in.

If it take it out in the Summer and beat on it hard, the pipe goes to about 500-600F, and the cylinder goes to 190*F. I measure about 180-190 on the radiator.

Temps measured with an infrared thermometer.


There are two things that cause overheating:

1.) OVerheating is caused by excess fuel washing the oil off the cylidner wall. The increased friction causes heat.

2.) excess fuel caused by ignition misfire.

Honda cycles are famous for crappy electrical wiring. My R was a nightmare to start and ran poorly till i eliminated the CDI plug.

I also found problems with the stock PJ that caused it to run too rich and overheat.

[Red Rider]

Jmack, is it actually overheating, or do you just feel that it runs too hot. If it's overheating, I would first check to see that the cooling system (radiators, water pump, & hoses) is in good condition & operating properly. The 85-89 250R's never had any recurring cooling problems that I've heard of, and I've never had any with my 86 ATC.

[jmack3986]

well the cylinder gets hot to touch i need to get a thermostat on it
i have a 188 main jet in it it has pt pipe fmf silencer and vforce reed cage 38mm airstricker carb it is 40 over on the cylinder with milled head any jet suggestions please help i am tired of messing with this

[jmack3986]

team geek you live in saint marys? you should go riding with us sometime.

[jmack3986]

well i raced it recently and i had no overflow and it kept blowing out water out of the overflow. so i am wondering what could have caused that. i might need a new cap

[3Razors]

Whatever geek. Im tired of hearing how every problem related to the 250r is from the ignition. Honda ignitions work just fine and are solid units.

[jmack3986]

what is the stock mainjet size on a 38mm keihin flatslide carb. info would be very useful. and my ignition system is fine. I have looked and looked for it but cant find nething

[Mr. Sandman]

Whatever geek. I'm tired of hearing how every problem related to the 250r is from the ignition. Honda ignitions work just fine and are solid units.
I'll 2nd that, in fact, everyone I know that has a Honda, new or old, does not or has not ever had a problem with crappy wiring/connections.

Jmack, check your impeller on the water pump, it could be shot and you're not getting the flow you need and get an overflow bottle if you don't have one. Adding a thermostat is unnecessary. A 188 main seems to be way to fat, especially with the minimal mods you have and your location. Try dropping down to a 165-175 to start and do a few plug chops and go up or down from there. With the milled head and higher compression, you may also need to run high octane race fuel so it'll run cooler (especially if it's detonating/pinging) .

[TeamGeek6]

well i raced it recently and i had no overflow and it kept blowing out water out of the overflow. so i am wondering what could have caused that. i might need a new cap

That happened to me in the desert when I covered the radiator and forgot to uncover it. It also had a leaky float then and was running very rich and flooding and gas was running out the overflow. It has to get pretty hot to blow out the excess.

New cap, maybe if the rubber is leaking.

Go to towerhobbies.com (R/C hobby website) and get an infrared thermometer for about $24 and measure the cylinder and radiator. About 190 on both is good. Im guessing that 215 or so will cause water loss.


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