Starting oping for yz250 jetting

41racing · Jan 31, 2016

Got a timbersled st mounted to my yz 250 2 stroke. Looking for a starting point on jetting. I have a jd jet kit and it's pretty vague on cold temps and high elevation. I'm thinking I will start with a 45 pilot 165 main and the lean needle in the 3rd clip. Will be riding west Yellowstone. This sound like a safe starting point? Disregard the title dumb ipad autocorrected and I can't change it.

portgrinder · Jan 31, 2016

i would go up on the main. at 6000ft in the summer i run a 175 main. mine has the pc2 pipe, rad valve and .025 cut off the head.

with a snowbike i have found you need to be richer on the main and needle than you think, as you are working the bike alot harder.

with a tire on, you can only load the motor so hard for so long. not so with a track kit.

dirtrebel · Jan 31, 2016

portgrinder said:
i would go up on the main. at 6000ft in the summer i run a 175 main. mine has the pc2 pipe, rad valve and .025 cut off the head.

with a snowbike i have found you need to be richer on the main and needle than you think, as you are working the bike alot harder.

with a tire on, you can only load the motor so hard for so long. not so with a track kit.

x2^^^ 180 main was my goto at 8000 ft on snow, with a free air breathing snow intake and long wot pulls. your results may vary but I run 160 in summer loafing on singletrack at 8000 feet, and a 180 in winter for wot on the pipe biking EDIT: CHECKED MY NOTES 180 WAS THE GOTO

41racing · Jan 31, 2016

I ran the bike at the st Anthony dunes this fall with a 172 main and it was pig rich. It's about 5k ft there if I remember right. So maybe start somewhere in the 170-172 area?

41racing · Jan 31, 2016

dirtrebel said:
x2^^^ 190 main was my goto at 8000 ft on snow, with a free air breathing snow intake and long wot pulls. your results may vary but I run 160 in summer loafing on singletrack at 8000 feet, and a 190 in winter for wot on the pipe biking

Wow didn't realize a guy would need to be that rich. Guess I better pick up a few more jets.

dirtrebel · Jan 31, 2016

41racing said:
Wow didn't realize a guy would need to be that rich. Guess I better pick up a few more jets.

like I said your results may vary, but with a free air intake and holding it wide open for 2-3 minutes at a time.......

also 20 below or 20 above? west yellowstone has both, cold day richer, warm day leaner, around 180 size main plus or minus gets both done, there's no way to get dialed without trying a few. different days different plays, if I rode a 2 stroke day in day out, and lived here (near west yellowstone) I would get it close on the rich side at 8000 and 20 degrees and call it good.

dirtrebel · Jan 31, 2016

41racing said:
I ran the bike at the st Anthony dunes this fall with a 172 main and it was pig rich. It's about 5k ft there if I remember right. So maybe start somewhere in the 170-172 area?

I'm sure that will get you going, just be aware and u will be fine, if you find yourself saying "damn i'm really flogging this thing", then stop and check. the main thing is being willing to let off or stop to make a change. In my experience you only burn down when you aren't willing to stop, you generally know its coming, lol

n16ht5 · Jan 31, 2016

start with stock jetting. stock keihin jets. THEN go from there

41racing · Jan 31, 2016

n16ht5 said:
start with stock jetting. stock keihin jets. THEN go from there

10-4 on that one. I won't buy aftermarket jets, I can't afford the trouble they bring. Haha

needpowder · Feb 1, 2016

For what it's worth, my CR 500 manual stated that my jetting for 4 to 5000 feet 80 to 100 degrees was exactly the same as 8 to 10,000 feet 20 to 40°. Made it pretty easy for me. I just dialed my bike in the summer and it was right on in the winter. I thought about going a little richer just to be safe, but after checking my plug it was perfect.

CATSLEDMAN1 · Feb 1, 2016

yz250 sno bike

I have a yz250 with 136 LT
BOYSEEN RAD VALVE
FMF PIPE AND MUFFLER
HOT WATER ON CARB
4" PLASTIC TUBE WITH FROGSKINZ FOR AIR FILTER

I STARTED WITH STOCK JETTING TOP TO BOTTOM, ran great, checked plugs and piston wash, all good, my engine was pieced together from parts but carb was off an 06. two or four I haven't found much different in jetting for the cold or long runs.

41racing · Feb 1, 2016

CATSLEDMAN1 said:
I have a yz250 with 136 LT
BOYSEEN RAD VALVE
FMF PIPE AND MUFFLER
HOT WATER ON CARB
4" PLASTIC TUBE WITH FROGSKINZ FOR AIR FILTER

I STARTED WITH STOCK JETTING TOP TO BOTTOM, ran great, checked plugs and piston wash, all good, my engine was pieced together from parts but carb was off an 06. two or four I haven't found much different in jetting for the cold or long runs.

Thanks for the info. I believe 178 is stock for my bike I'll try that and see how she goes.

41racing · Feb 1, 2016

CATSLEDMAN1 said:
I have a yz250 with 136 LT
BOYSEEN RAD VALVE
FMF PIPE AND MUFFLER
HOT WATER ON CARB
4" PLASTIC TUBE WITH FROGSKINZ FOR AIR FILTER

I STARTED WITH STOCK JETTING TOP TO BOTTOM, ran great, checked plugs and piston wash, all good, my engine was pieced together from parts but carb was off an 06. two or four I haven't found much different in jetting for the cold or long runs.

Just curious how much gas do you burn in a day riding? I got a 3.2 tank and a can that holds 3 I'm worried it won't be enough.

portgrinder · Feb 1, 2016

that will be good for most days. unless you have a long trail in and out / arent keeping up to sleds

Yrocmoto · Feb 2, 2016

I'm running mostly stock with a squish adjusted head and v-force reeds. I've settled on 172, 1st clip and 45p. I get a slight 'rattle' in the pipe at about 3/4 throttle, so might go with a 175. Mixing gas at 36:1. 20-30 degrees, 8000'.

portgrinder · Feb 2, 2016

Yrocmoto said:
I'm running mostly stock with a squish adjusted head and v-force reeds. I've settled on 172, 1st clip and 45p. I get a slight 'rattle' in the pipe at about 3/4 throttle, so might go with a 175. Mixing gas at 36:1. 20-30 degrees, 8000'.

Thats detonation. you need more octane. trust me.

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Starting oping for yz250 jetting

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