Posts
3945
Joined
4/1/2008
Location
Visalia, CA, USA
Edited Date/Time
5/29/2014 8:06pm
A friend of mine is chasing excessive heat issues with his 07 CRF250X. At this point, there's not much X left of it. Heavily ported head, aftermarket cam, 13.5 piston, 250R jetting (45 pilot, 07 250R needle, 195 main), full Yosh exhaust.
The bike has always run a bit on the hot side, but recently he went from a 13:1 to 13.5:1 piston and opened up the ports a bit more than they'd been over the last year. Since then it's gotten way too hot. He will see 250f right / 230f left on the radiators with a laser temp gun, and he's now struggling to get it jetted right.
I'm thinking he's gone over the edge with the compression, and mixing 100ll with pump 92 would be a good solution. Ive been running it 100% in my pingers for a couple years with great success, but he's thinking it'd be bad in a thumper. He's trying to avoid race gas due to the cost.
Thoughts or suggestions?
The bike has always run a bit on the hot side, but recently he went from a 13:1 to 13.5:1 piston and opened up the ports a bit more than they'd been over the last year. Since then it's gotten way too hot. He will see 250f right / 230f left on the radiators with a laser temp gun, and he's now struggling to get it jetted right.
I'm thinking he's gone over the edge with the compression, and mixing 100ll with pump 92 would be a good solution. Ive been running it 100% in my pingers for a couple years with great success, but he's thinking it'd be bad in a thumper. He's trying to avoid race gas due to the cost.
Thoughts or suggestions?
I'm wondering if anyone has firsthand positive or negative experience with 100ll in a thumper.
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What kind of temps are you guys seeing at the radiator top when coming off the track?
If it is pushing coolant out do not jump straight to a higher pressure radiator cap. You will be masking the prob. The bike should not boil over in typical situations. I'm thinking you are super lean from a passage being blocked in the carb or the hot start being stuck partially open or something like that. 195 is a ridiculously huge main. There is no way it should be running lean with that. Seems like an air leak to me.
The bike was boiling over, but he put new gaskets in, along with new studs, and had the head surfaced. That's when they also ported the head a bit more than it already was, and went from a 13:1 to 13.5:1. He's running a 1.7 cap, and has tried Enigne Ice, but has gone back to regular coolant/distilled water.
Interestingly, he called James Dean who said that with his level of mods, a 195-200 main is probably about right. It starts and idles like a champ, leading me to think there's not an air leak. Of course, if I really knew it'd be fixed already.
Personally, I'm not convinced it's lean. My personal hypothesis is either detonation or a really tiny non-visible crack in the head. We're going to give 100ll a shot this week and see if the temps drop.
If any of you thumper guys get a chance to check your rad temps, that would be super. I can't do so, as all my race bikes are pingers (the CRF is my friend's bike, in case anyone missed that).
Main jet on a 250R is in the 162-175 range. I can't believe you'd be in the195-200 range even with those mods.
If it is detonation you will be able to hear it pinging. Lug it through a thick turn in 3rd gear and see what happens.
I would be trying to rule out any air leak. Carb boots, hot start, pipe joints, etc.
I just noticed this post is four years old.
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