Random overheat, no changes to provoke...what gives??

[YFZRob]

Hey guys. Yesterday I took my 250R out for some trail riding before next weekend's hare scramble. I was shocked to see after about 15 miles of riding, my ESR temp gauge read around 210 degrees. In 65 degree weather and riding really hard with good 30-40 mph or faster speeds, it should see 180 tops. I never get over 200 unless i'm in tight areas without much airflow across the radiator. I have changed nothing on the combo. 185 psi compression, PWR radiator with 16 psi cap (one included w/ radiator), pump gas, good jetting, 40:1 maxima super-m, plenty of coolant in the overflow tank.

So, after I noticed that, I kept an eye on it. After even more riding, it crept up to 240! I stopped, let it cool to 160, rode again....3 miles later, 250!! I let it cool to 190, released the pressure in the system, then fired it back up. This time, the temps dropped to 175ish and slowly crept back up to 210, but stabilized at 210 until I made it back to the trailer.

Anyway, I first though water pump, but when temps dropped after firing it up and riding again after the second cool down, it appears that isn't an issue. Then when I got home, I topped off the radiator and fired up the motor w/o the cap...you can see plenty of coolant flowing through the radiator, so the pump is fine. The whole way back to the truck after the 2nd cool down, I kept the throttle 1/4 and less. It got HOT when I was giving the main jet some work (normally what kept it cool), so could it possibly be an obstruction on the main jet making it run lean, therefore hot? Any other ideas?

Thanks!!

[LONG-ROD]

Could be, I would defintly check, also check for leaks around the intake, and you could do a preasure test, could have had a crank seal go had, the main jet is where a bad crank seal makes the motor go boom.

[C41Xracer]

is it a lean condition because of the cool weather?

[YFZRob]

I'm 99% certain it is not an intake leak, but I have the parts to test so I will check. I first will dig out the main jet and check for debris, then check for leaks while the carb is off. I know the jetting should be fine for the cooler air, but it's a slight possibility. I'll check the plug even though it won't be too accurate, and try going a size up on the main while I'm there.

[jcs003]

could be detonation. you seem to know your bike well, but you may have some bad fuel. just my thought.

[BERT306]

off topic here.......is that the R u race in your sig?? that thing is CLEAN!!!! NICE BIKE man!


ok back to the issue.....

[YFZRob]

I don't think it was detonating...it sounded crisp and clean. But that could be a possibility. I just need to dig more and test more to hopefully find something.

Yes, the quad in my sig is the one I race. Just hare scrambles so it's not getting any more abuse than aggressive trail riding. It was just collecting dust in my garage and getting used 2 times a year before...now it's being used at least. It was either sell it and get a KTM XC quad or race it...I just couldn't let it go.

It's not nearly as close to stock as the photo shows...I've got just the minimum on it for power, handling, and protection. Still looks stock other than the pipe, nerf bars, handle bars, and Maxxis tires. A lot of the parts I replaced with aftermarket items just to preserve the OEM stuff.

[jhtrx250r]

sounds like fuel issue or a air leak, in oregon we have what they call winter fuel right now it is 10% ethinol give or take a little, It makes bikes,quads and cars run very hot!
also check your main seal on the mag side, I have had these go bad and cause air leaks, take off the cover if you see or smell any evidence of gas you found your leak. I replace this crank seal every year on all my 250r's it is a $12 seal from honda, dont buy an aftermarket one.

[YFZRob]

Originally posted by jhtrx250r
sounds like fuel issue or a air leak, in oregon we have what they call winter fuel right now it is 10% ethinol give or take a little, It makes bikes,quads and cars run very hot!
also check your main seal on the mag side, I have had these go bad and cause air leaks, take off the cover if you see or smell any evidence of gas you found your leak. I replace this crank seal every year on all my 250r's it is a $12 seal from honda, dont buy an aftermarket one.

Good info....thanks! All the pumps here in Florida have stickers now that say "may contain up to 10% ethanol or less" so maybe I got a bit of fuel that was a full 10% ethanol and it caused this crap. I will do an air leak test today and then address the carb and fuel. I may just buy some race fuel and go from there if there aren't any air leaks.

[LONG-ROD]

This may be a little off topic, but from what i remember, 2 strokes became estinct in AMA MX raceing do to a lead rule the AMA put ino effect to help bring on the 4 stroke era. This stated you could only run 2.8% lead. and from what I have read lead is what makes two stroke fast, so why do people run unleaded fuel in there 2 strokes, VP makes fuel with octanes as low as 85 with lead.

[YFZRob]

Originally posted by LONG-ROD
This may be a little off topic, but from what i remember, 2 strokes became estinct in AMA MX raceing do to a lead rule the AMA put ino effect to help bring on the 4 stroke era. This stated you could only run 2.8% lead. and from what I have read lead is what makes two stroke fast, so why do people run unleaded fuel in there 2 strokes, VP makes fuel with octanes as low as 85 with lead.

Because leaded fuels are not cheap. I built this motor to run on pump gas since I have a KTM 2-stroke as well that runs on pump gas...at $2 a gallon, it beats most VP fuels that are $8+ a gallon.

[jcs003]

Originally posted by jhtrx250r
sounds like fuel issue or a air leak, in oregon we have what they call winter fuel right now it is 10% ethinol give or take a little, It makes bikes,quads and cars run very hot!
also check your main seal on the mag side, I have had these go bad and cause air leaks, take off the cover if you see or smell any evidence of gas you found your leak. I replace this crank seal every year on all my 250r's it is a $12 seal from honda, dont buy an aftermarket one.

race fuels are solely for high compression engines. lead was an additive in early fuels to increase the octane rating. (tetra-ethyl lead). this is what is used in race fuels or a deriviative of to get them up to, 110, 112, 118, etc..

[LONG-ROD]

I disagree with you on your comment race gas is for high compression motors. High octane fuel is for high compression motors. If you had a 50,000 + turbo engin in your rally car,or truck, which is a low compression motor, you would not put pump gas in it. but somthing like VP rally plus which is 89 octane You would run race gas of some kind, because it is a clean fuel made in small batches. And like posted before it has diffrent properties like specific gravity and density. Many super bikes run on lower octane race gas as well. A good choice for him would be VP U4e it is 93 octane with a specific gravity of .718 at 60 degree F and is a leaded fuel. for refrence VP 110 is 107 octane and has a specific gravity of .720 -.735 at 60 degree F

[YFZRob]

Originally posted by LONG-ROD
I disagree with you on your comment race gas is for high compression motors. High octane fuel is for high compression motors. If you had a 50,000 + turbo engin in your rally car,or truck, which is a low compression motor, you would not put pump gas in it. but somthing like VP rally plus which is 89 octane You would run race gas of some kind, because it is a clean fuel made in small batches. And like posted before it has diffrent properties like specific gravity and density. Many super bikes run on lower octane race gas as well. A good choice for him would be VP U4e it is 93 octane with a specific gravity of .718 at 60 degree F and is a leaded fuel. for refrence VP 110 is 107 octane and has a specific gravity of .720 -.735 at 60 degree F

I'm not trying to get into a technical discussion on race fuels, particularly when we're referring to a 250R motor specifically here. If you're spending $8+ a gallon, why try and special order something like an 89 octane fuel when a simple 110 leaded will work worlds better than any pump gas? In all of Orlando, I'm not going to find a fuel like that...something like C16 is much more common. Yes, all race fuels are better than pump gas no matter what the octane.

As far as my motor goes, everything checked out. This motor is stout as always...it would hold 10 psi for an eternity...there are zero air leaks. Swapped plug, jumped to a 180 main from a 178, and will get 5 gallons of whatever race gas I can source now.

Thanks again for everyone's support.

[LONG-ROD]

sorry man where I live there is a old man that sells vp and has about what ever you need and the lower octane stuff is like 4.50 a gal 110 is like 6.00 did not think it might be more difficult for some to obtain or cost more. I was refering to what jcs003 said about race gas is for high compression only, I figured you said you run pump gas so you have a lower compression motor and you said it was not pre detinateing you surly would not run good on 110, and certinly not C16 which is 117 octane, just letting you know there are low octane race fuels for your applacation that would be better for the longgevity of your motor.

[jcs003]

specific gravity is used to determine the true mass of the fuel. they know what waters specific gravity is and they use a ratio to determine purity. not to argue but a race fuel sitting for a few weeks will have its specific gravity change. and if i remember from school. 64 degrees is equal to 1.0 specific gravity

[LONG-ROD]

never siad it would not change, there is no telling how long this stuff sitts before we get it, lol oh well it's not life or death, well maybe for the machine.

[LONG-ROD]

Rob have you ever used the product by VP called cool down? they claim to lower temps up to 50 F I might try it.

[YFZRob]

Originally posted by LONG-ROD
sorry man where I live there is a old man that sells vp and has about what ever you need and the lower octane stuff is like 4.50 a gal 110 is like 6.00 did not think it might be more difficult for some to obtain or cost more. I was refering to what jcs003 said about race gas is for high compression only, I figured you said you run pump gas so you have a lower compression motor and you said it was not pre detinateing you surly would not run good on 110, and certinly not C16 which is 117 octane, just letting you know there are low octane race fuels for your applacation that would be better for the longgevity of your motor.

Ah, I didn't know that. I will talk to my local VP dealers and see if I can get them to carry some of the lower octane fuels. I have considered many other VP options and they just don't exist around here. thanks for the info!

[YFZRob]

Originally posted by LONG-ROD
Rob have you ever used the product by VP called cool down? they claim to lower temps up to 50 F I might try it.

Nope...haven't heard of it...I'll look into it!