CR250 Overheating

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2/9/2020 5:09 AM

I have a CR250 that had been modified with the Eric Gorr 265 big bore kit. Yesterday I competed in an extremely muddy hairscramble event and almost didn’t finish due to the bike overheating. I’ve never had this happen before and assume it’s bc of the very muddy conditions, getting the bike stuck and having to rev it out. Symptoms the bike had was boiling over through the radiator overflow (I use engine ice also), bike losing bottom end power, and engine rattling/ticking. I have another race coming up in two weeks and plan on tearing the bike down and replacing the piston/rings. Is there anything else I should check/replace that could have been effected by my engine overheating like that? Any reason to split cases and dig into the bottom end?

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2/9/2020 11:35 AM

Look into adding a fan. I don't know if you can add one straight away or if you need to mod your ignition and add a battery. I had an 05, seems like a tough bike to ride hare scrambles with because of the power delivery.

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The older I get, the faster I was.

2/9/2020 11:51 AM

captmoto wrote:

Look into adding a fan. I don't know if you can add one straight away or if you need to mod your ignition and add a battery. I had an 05, seems like a tough bike to ride hare scrambles with because of the power delivery.

Yeah I’ll have to look into adding a fan. It’s not the easiest bike to ride a hare scramble on but I enjoy riding the ol’ 2 strokes and I’m trying not to spend a bunch of money on a new bike.
My intent is to rebuild the top end after the overheating episode (new piston and rings). Is there anything else I may need to check that could be affecting by overheating....is it worth splitting the cases to check the bottom end?

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2/9/2020 5:37 PM

Check your clutch. My friend chased an overheating issue for quite some time on his 250F, it ended up being plates and springs that were slipping just enough to create lots of heat, but not enough to be really noticeable from a power perspective.

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2/10/2020 5:00 AM

Tad richer on jetting and higher pressure cap like used on the 4 strokes . Kaw are 1.6 psi I believe. Jetting because of detonation

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2/11/2020 7:31 PM

Low speed air flow and radiators full of mud will reduce cooling. A 2 stroke will usually start pinging letting you know its getting really hot.

Japanese OEM caps are typically 1.1 Bar

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2/13/2020 8:24 PM

Don't know if you're using a Mikuni TMX carb but if you are my bet would be carb/jetting issue.

I have an 03 with the stock TMX I ran round and round trying to find decent settings and occasionally had overheating that I firmly believe where related to carb and jetting.

I finally found a local JD jetting Keihn Airstryker carb I snatched up for a killer price and haven't had a hint of overheating or surging after wide open uphills or other extended full throttle situations.

Good luck and thanks for keeping America 2 stroke!

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