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WR is a raging monster in cool weather

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It's been a little over a month since I had a chance to do any riding. Work has been crazy, the holidays, one thing then another.

Since I last got to ride, I changed the oil and filter, slapped in a new air filter with BelRay blue on it, made sure the carb was drained, running fresh premium pump gas etc. Mainly general maintenance stuff.

I planned on riding with a bud tomorrow and part of the weekend, but tomorrow isn't going to work due to other things needing to be taken care of first.

So, I decided to take a little spin around the neighborhood just to warm up the bike, make sure it was running spot on, make sure there were no leaks, battery was fully charged, checked air pressure etc..

There is a small place to ride around what used to be a baseball diamond, no jumps etc, just a field.

I hit the dirt and wicked up the gas just to see if the AP was still working as it should, leak jet was set right and in general get at least 5 minutes of seat time.

The last time I rode, temps were in the mid to upper 80's. Today, temps are in the low 60's.

The WR was unbelievable. Strong ain't the word for it, crazy explosive is more like it. I was sitting in the middle of the seat, third gear, going slow and blipped the throttle maybe 1/4 and the damn thing nearly looped out on me. I was thinking damn, the traction here must be fantastic.

I rolled over to an area with a little gravel and twisted it up again just a little. I was holding with my knees, forward stance on the pegs and weight over the rear of the tank. The bike stood straight up and I started to whiskey throttle and nearly came off the back, luckily I had a foot over the brake and was able to hit it just in time to save it.

Last time out, the bike ran fine, but nothing near the absolutely explosive power coming out of it today.

The only thing I can think of is the new air filter and cooler temps have a positive effect. I'm going go ride Saturday and I'm wondering if I need to ride over on the kiddie loop so I don't kill myself or worse.

Carb is setup as follows :

Model (YZ or WR 250F): WR250F 2009

Timing (WR-YZ): YZ

Main jet: 180

Pilot Jet: 45

Leak Jet: Stock Leak Jet blocked off

Fuel screw (turns out): 1½ turns out

Needle model/Clip position: JD Red needle 3rd clip from top (JD Kit #JDY011)

Airbox lid (on or off): OFF

Pipe: 2008 YZ250F stock head pipe and can

I'm running 13/52, free mods. Other than that, pretty much stock.

It's not like this bike was a dog before, it wasn't. It's just crazy strong now and I haven't done anything to it other than some routine maintenance.

Why the change in power ? Will the temps being lower make THAT much of a difference in power delivery ?

Somebody school me here because I'm thinking maybe Santa sprinkled some magic dust on this thing. I'm OK with the extra power, I just have to realign what I expect when I twist it up.

I'd love to say I'm so cool I handled the situation, but the truth is, I got real lucky I didn't loop out - twice.

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The colder weather will lean out the jetting. Quite possibly the jetting you have may not be spot on for temps in the 80's, but rather more adequately jetted as it is for these cooler temps. I may be mistaken with this next comment so be sure to double check. I'm new to 4 strokes. I think I read guys running MJ in the 160-170 range and stock pilot for summer weather. If I read correctly then ur current jetting would be more suitable for these temps. Again, double check with a more experienced 4 stroker. I'm still learning myself. Awesome about the power boost though!!

(If I am mistaken then please somebody correct me. I need to learn. thx.)

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It's definitely the carb settings. It's not just the air temp but also humidity and barometric pressures as well. You could either keep moving to different areas of the world so the temp, pres., and humidity are always the same or tweak your carb all year round to get the effect

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It's definitely the carb settings. It's not just the air temp but also humidity and barometric pressures as well. You could either keep moving to different areas of.

the world so the temp, pres., and humidity are always the same or tweak your carb all year round to get the effect

+1

LoneStar, I remember reading some of your earlier posts and I thought you needed to keep on testing on your jetting as I thought you were still rich. I think you've confirmed my suspicions Both Sunruh and me run leaner settings than what you have. sunruh has had his jetted on a dyno with an O2 sensor and mine was testing with the butt dyno .

We are both in Austin.

Try this: PJ 40, Jd needle Ok @ 3rd , 180 or 182 MJ. I've a 45 LJ as the OEm 75LJ had a bog. During testing i'd just roll the throttle on to keep the LJ out of the equation.

I change the MJ every 15-20 deg in temp change.

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It's definitely the carb settings. It's not just the air temp but also humidity and barometric pressures as well. You could either keep moving to different areas of the world so the temp, pres., and humidity are always the same or tweak your carb all year round to get the effect

Looks like living in a trailer all my life is about to pay off :bonk:

Thanks OnB for the suggestions. I'm already running a 180 MJ, but will definitely pick up a 40 pilot.

I've suspected the PJ is a little fat since I've been able to run with the fuel screw 1/2 turn out. Swede suggested the same a while back, I just forgot to put that on my list of things to do (soon).

I was simply amazed at the difference when the only thing I can attribute the change to is temps. It's going to be about the same temp for the next couple of days, then drop down another ~10 degrees or so both days and overnight.

It was 60 or so today and the bike is still on steroids.

We'll be riding where the Red Bull Last Man Standing series is run up in Bulcher TX. Plenty of room to ride, and plenty of easy places to land softly.

I will see if I can pick up a 40 PJ on the way out in the morning

Thanks again for the suggestions.

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That crisp "on steroids" sensation in cooler weather is so nice. Reminds me of my reverse temperature sensitive gun powder: in cooler weather the power factor goes up quite a bit and in hot weather the feet per second is sluggish.

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