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Discussion Starter #1
2004 RM 250 running hot.

8 months back I rebuilt the top end with a Wisco pistion kit. The bike ran hot for a while and then seemed to break in and cool down a bit. It seems to be back up recently. The symptoms are uneven reving (pinging) and then after that it runs off...looong reving. I realize the long reving is probably atomization of the fuel or pre ignition. I let it cool but then it just seems to get back up in the uneven reving stage again. It will run like that all day and never really boil over very hard...
I have tried:
-The fancy coolant
-Overflow bottle
-Lastly, changed the jetting to run one notch richer.

I do ride in hawaii which is like slow single track in a warm swamp. Yeah a hot environment but my friends bikes dont have this much trouble. I do have those stock plastic fins on the fins of the raidators too (air flow problem??)

Running Belray at 50:1 with 87 octain gas..
 

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Old School but still Cool
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Check the head for warping. Check the cooling circuit to see if the water pump is operating correctly. Make sure the o-rings on the head seated in the grooves correctly.
 

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sounds like your running lean, how does your plug look?.. prolly need to up them jets or you have a airleak..
 

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Run 91 octane fuel or even some avgas 100LL and it will run cooler. You shouldn't have to change the jetting but maybe the pilot. The idle problem could be the pilot jet is too big or too small. What pipe and jetting are you running?
 

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Discussion Starter #5
sounds like your running lean, how does your plug look?.. prolly need to up them jets or you have a airleak..
How do I check for a airleak?
Plugs seem good. I did move the jet clip down one so its one up from the bottom. I wanted to see if running richer cooled it down. All it did was smoke alot and still ran hot. Would leaning it out cool it down?

"Check the head for warping. Check the cooling circuit to see if the water pump is operating correctly. Make sure the o-rings on the head seated in the grooves correctly."
Whats the best way to test the cooling circuit? I'll check the head and ring position.

"Run 91 octane fuel or even some avgas 100LL and it will run cooler. You shouldn't have to change the jetting but maybe the pilot. The idle problem could be the pilot jet is too big or too small. What pipe and jetting are you running?"
I'll try higher octane fuel. I assumed the more octane the hotter it burned, my bad. I'm running stock pipe and jetting. Only change was the one notch richer on the jet.

Keep it coming guys. I dont get this nailed im going to lauch this pile into the ocean. I will never heat up again!! :) The reality is I have a track bike and i need a trail bike. KTM here i come.
 

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The reality is I have a track bike and i need a trail bike.
Trade it for a trail bike. THere is someone out there that bought a trail bike and want's a track bike.
 

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Old School but still Cool
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To check the head: Remove it from the cylinder and take a straight edge and lay it from hole to hole and run a .008 feeler guage under the straight edge and see if their is a gap.
To check the Cooling circuit: Borrow or buy a pressure tester. It goes on the radiator cap and has a guage to tell you if it holds pressure. I would go to like 3 or maybe 5 lbs and see if it drops rapidly.
On the leaning issue others have said, do a plug chop. Might have seal issues if it is leaning out on you.
 

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To check for an air leak, start the bike and let it idle then spray ether around the intake and cylinder and see if the bike rev's up. If it rev's up pay attention to where the spray went and you found the air leak. It might also show signs of the ether bubbling if enough is sprayed on the leak.
 

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1986 Honda TRX 250r
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check and make sure your water pump isint al coroded from hard water. that happens a lot to old motorcycles. and your jetting has to be off. did you change all your jets to a richer size or just change the slide?
 

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Discussion Starter #11
With a stock pipe set-up,I'd check the silencer to see if its plugged!!
Ha well I just stuck my finger in the silencer and found the tube broken off to the end piece. It was lined up perfectly just broken off. It shouldnt have been restricting any air but i'll change it out anyway.

As far as an air leak.... I'll try the ether test. Could this be symptom of bad reeds?

Thanks
 

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my 96 rm 250 did the same thing ...ran rich and revved by itself ....it had a broken reed so id check them too
 
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