YZ 250 Revvs out fast, goes flat on top end

Spagina767
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Spagina767
Edited Date/Time 12/10/2015 5:20pm
I have a very low hour 2006 YZ 250, and just rode it for the first time. Bike is all stock except for a PC Factory Sound silencer.

Pilot jet : not sure, stock i imagine.
Main jet : 172
Fuel: 100LL AV gas 45:1 with Honda HP2

The bike doesn't feel like the clutch is slipping, and isn't notxhy. Has great low/ mid but feels like it is riding super high in the RPM's for what gear I'm in.

Gearing is 13:51, 1 up in rear from stock. I BARELY use 2nd gear, some 3rd, and a LOT of 4th.

Am I just super used to 4 strokes or what? I don't remeber having to use 3rd in 90% of corners and 4th gear a lot. I even get real close to 5th... On a MX track!
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IceMan446
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IceMan446 11/20/2015 2:47pm
11/20/2015 2:47pm
Its a two stroke man. Better get used to it.

I ran a 13/50 on my YZ250 and had to use 3rd and 4th a lot. I tried a 49 tooth rear and it wasnt enough in the super tight corners. A 51 would make the gears even shorter, so try going down a tooth in the rear.

Pilot jet should be a 48. Double check though.

Try a GYTR flywheel weight, helped me a bit with just rolling on the throttle coming out of corners and not having to shift as quickly.
Paw Paw 271
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Paw Paw 271 11/20/2015 3:25pm
11/20/2015 3:25pm
Do a chop test and do a reading on the spark plug. I suspect you are rich on top end and the plug will look black.

Paw Paw
Polishhammer 11/20/2015 4:26pm
11/20/2015 4:26pm
When I had a yz250 I did not like 51 rear sprocket. Run 14/49 or 14/50. The shorty silencer kills topend too on that bike.
mb
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mb 11/20/2015 4:43pm
11/20/2015 4:43pm
The 13T is your problem. 14 will stretch it out (provided your engine is running well). I run 14/51 and feel well geared for any situation.

The Shop

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Spagina767
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Spagina767 11/20/2015 6:36pm
11/20/2015 6:36pm
IceMan446 wrote:
Its a two stroke man. Better get used to it. I ran a 13/50 on my YZ250 and had to use 3rd and 4th a lot...
Its a two stroke man. Better get used to it.

I ran a 13/50 on my YZ250 and had to use 3rd and 4th a lot. I tried a 49 tooth rear and it wasnt enough in the super tight corners. A 51 would make the gears even shorter, so try going down a tooth in the rear.

Pilot jet should be a 48. Double check though.

Try a GYTR flywheel weight, helped me a bit with just rolling on the throttle coming out of corners and not having to shift as quickly.
I have an 11oz but wanted to get used to it stock, so I can make sure I know how the bike works both ways. A few more rides then I'll add it on.
Spagina767
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Spagina767 11/20/2015 6:38pm
11/20/2015 6:38pm
Paw Paw 271 wrote:
Do a chop test and do a reading on the spark plug. I suspect you are rich on top end and the plug will look black...
Do a chop test and do a reading on the spark plug. I suspect you are rich on top end and the plug will look black.

Paw Paw
I'll check that. It had a 178 in it, and was definitely rich. It cut out high RPM's.
Put a 172 in and it felt much better.
Spagina767
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Spagina767 11/20/2015 6:41pm
11/20/2015 6:41pm
mb wrote:
The 13T is your problem. 14 will stretch it out (provided your engine is running well). I run 14/51 and feel well geared for any situation.
Yeah I just started reading and realized that stock gearing is 14/50 ... I was thinkin it was 13/50. So by adding a tooth, I'm essentially at 14/54.... No wonder it's revving out fast. Man I feel stupid. I'll be ordering a 14T front sprocket on Monday.

I'm also buying a v-force 3 reed valve so that should help too.
Spagina767
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Spagina767 11/20/2015 6:42pm
11/20/2015 6:42pm
Polishhammer wrote:
When I had a yz250 I did not like 51 rear sprocket. Run 14/49 or 14/50. The shorty silencer kills topend too on that bike.
I have the factory sound silencer not the r-304, so it's still very long.
FGR01
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FGR01 11/20/2015 7:42pm
11/20/2015 7:42pm
I have the same bike. My advice is to run 32:1. If for no other reason, other people's jetting specs will mean something to you since that is what is recommended in the bike. At 45:1, you are basically having to run the main so much leaner than stock to compensate for the lack of oil making your fuel/air ratio richer.

I usually run 100 unleaded pump race gas. I tried 5 gallons of 100LL one time. It was kind of strange, I had to lean the pilot as it felt sluggish on the initial response but I had to richen the main as it was lean on top. Wasn't bad, just a little weird. I went back to the 100 pump gas since I already had my jetting dialed for that.
Spagina767
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Spagina767 11/21/2015 1:24am
11/21/2015 1:24am
FGR01 wrote:
I have the same bike. My advice is to run 32:1. If for no other reason, other people's jetting specs will mean something to you since...
I have the same bike. My advice is to run 32:1. If for no other reason, other people's jetting specs will mean something to you since that is what is recommended in the bike. At 45:1, you are basically having to run the main so much leaner than stock to compensate for the lack of oil making your fuel/air ratio richer.

I usually run 100 unleaded pump race gas. I tried 5 gallons of 100LL one time. It was kind of strange, I had to lean the pilot as it felt sluggish on the initial response but I had to richen the main as it was lean on top. Wasn't bad, just a little weird. I went back to the 100 pump gas since I already had my jetting dialed for that.
I can't find 100 reasonably close to me. The best thing I can find is 100LL. I've thought about going to a marina and getting 5gal non ethanol 93 and mix it with 5gal 100LL to make something like 97 LLL.

That's a good point regarding jetting. I typically ran 40:1 (one 16oz bottle of oil to 5 gallons... Just super easy), and may go back towards that.
HackMan162
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HackMan162 11/21/2015 7:40am
11/21/2015 7:40am
I always ran yamalube 2r at 40:1 in my YZ250s. Never had a lubrication failure. In my experiences, 100LL is difficult to get spot on with jetting. A switch to VP 110, or premixed T2 makes it easier, at a cost $$$. I didn't care for the Vforce on my YZs. I ran stock or Boyesen. Other guys like them, so ymmv.
Premix
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Premix 11/21/2015 8:50am
11/21/2015 8:50am Edited Date/Time 11/21/2015 8:54am
Yz stock jetting is super rich. I'm running VP110 32:1 Castor 927.

Try:
BR9EG plug (stock is BR8EG)
1-2 sizes smaller on pilot
Clip up to top notch on needle
168 main
Air screw 1- 1.75 turns out

Pull the plug. Jet it until the plug is brown turning white. This plug is even a little rich for my liking but will give you a good visual

Kenny Boy
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Kenny Boy 11/22/2015 11:00am
11/22/2015 11:00am
I Agree 13/51 is your problem. get a 14.
Spagina767
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Spagina767 11/22/2015 1:17pm
11/22/2015 1:17pm
Thanks guys.

Ordering a 14T front sprocket, and throwing a VForce 3 on this week.

I can find ethanol free 93 close to me - think I should mix 100LL and 93 Non-E?

I just can't justify race gas because it's nowhere close to me and I just don't want to spend a ton on canned race gas from a bike shop.
Premix
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Premix 11/22/2015 3:49pm
11/22/2015 3:49pm
Spagina767 wrote:
Thanks guys. Ordering a 14T front sprocket, and throwing a VForce 3 on this week. I can find ethanol free 93 close to me - think...
Thanks guys.

Ordering a 14T front sprocket, and throwing a VForce 3 on this week.

I can find ethanol free 93 close to me - think I should mix 100LL and 93 Non-E?

I just can't justify race gas because it's nowhere close to me and I just don't want to spend a ton on canned race gas from a bike shop.
Try the sprocket change then the v force. I'll be interested to know what differences you feel.

Send a picture of your plug after your done running it.
mxtech1
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mxtech1 11/24/2015 10:56am
11/24/2015 10:56am
Spagina767 wrote:
Thanks guys. Ordering a 14T front sprocket, and throwing a VForce 3 on this week. I can find ethanol free 93 close to me - think...
Thanks guys.

Ordering a 14T front sprocket, and throwing a VForce 3 on this week.

I can find ethanol free 93 close to me - think I should mix 100LL and 93 Non-E?

I just can't justify race gas because it's nowhere close to me and I just don't want to spend a ton on canned race gas from a bike shop.
Ethanol free 93 is plenty for a stock YZ250 motor. Very little difference between 100LL and 93 other than cost.

If you want better fuel, do it right and use your choice of VP @ a 50/50 mix with 93.
Spagina767
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Spagina767 11/24/2015 11:55am
11/24/2015 11:55am
Spagina767 wrote:
Thanks guys. Ordering a 14T front sprocket, and throwing a VForce 3 on this week. I can find ethanol free 93 close to me - think...
Thanks guys.

Ordering a 14T front sprocket, and throwing a VForce 3 on this week.

I can find ethanol free 93 close to me - think I should mix 100LL and 93 Non-E?

I just can't justify race gas because it's nowhere close to me and I just don't want to spend a ton on canned race gas from a bike shop.
mxtech1 wrote:
Ethanol free 93 is plenty for a stock YZ250 motor. Very little difference between 100LL and 93 other than cost. If you want better fuel, do...
Ethanol free 93 is plenty for a stock YZ250 motor. Very little difference between 100LL and 93 other than cost.

If you want better fuel, do it right and use your choice of VP @ a 50/50 mix with 93.
I read so many conflicting stories on 100LL, so I just wasn't sure. No race pump gas around me and canned fuel is ridiculous..
mxtech1
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mxtech1 11/24/2015 2:30pm
11/24/2015 2:30pm
Spagina767 wrote:
Thanks guys. Ordering a 14T front sprocket, and throwing a VForce 3 on this week. I can find ethanol free 93 close to me - think...
Thanks guys.

Ordering a 14T front sprocket, and throwing a VForce 3 on this week.

I can find ethanol free 93 close to me - think I should mix 100LL and 93 Non-E?

I just can't justify race gas because it's nowhere close to me and I just don't want to spend a ton on canned race gas from a bike shop.
mxtech1 wrote:
Ethanol free 93 is plenty for a stock YZ250 motor. Very little difference between 100LL and 93 other than cost. If you want better fuel, do...
Ethanol free 93 is plenty for a stock YZ250 motor. Very little difference between 100LL and 93 other than cost.

If you want better fuel, do it right and use your choice of VP @ a 50/50 mix with 93.
Spagina767 wrote:
I read so many conflicting stories on 100LL, so I just wasn't sure. No race pump gas around me and canned fuel is ridiculous..
Get the jetting right for 93 and you'll be fine!

Pit Row

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Spagina767
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Spagina767 11/24/2015 4:09pm
11/24/2015 4:09pm
mxtech1 wrote:
Ethanol free 93 is plenty for a stock YZ250 motor. Very little difference between 100LL and 93 other than cost. If you want better fuel, do...
Ethanol free 93 is plenty for a stock YZ250 motor. Very little difference between 100LL and 93 other than cost.

If you want better fuel, do it right and use your choice of VP @ a 50/50 mix with 93.
Spagina767 wrote:
I read so many conflicting stories on 100LL, so I just wasn't sure. No race pump gas around me and canned fuel is ridiculous..
mxtech1 wrote:
Get the jetting right for 93 and you'll be fine!
I've always read that the YZ's are prone to knocking/ detonating on 93 & need a few more octane or the head cut. And I may not be pro but I can ride, so the bike is working hard (sometimes). Also I don't want to run ethanol fuel, I haven't had great luck with it.

coastlinecascott 11/24/2015 5:21pm
11/24/2015 5:21pm
Im running 100ll 172 main 48 pilot 2nd position needle 11 oz fly wheel 32 to 1 lucas oil. Br8eg plug. Runs perfect. Socal Mx only .
FGR01
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FGR01 11/29/2015 8:59pm
11/29/2015 8:59pm
Premix wrote:
Yz stock jetting is super rich. I'm running VP110 32:1 Castor 927. Try: BR9EG plug (stock is BR8EG) 1-2 sizes smaller on pilot Clip up to...
Yz stock jetting is super rich. I'm running VP110 32:1 Castor 927.

Try:
BR9EG plug (stock is BR8EG)
1-2 sizes smaller on pilot
Clip up to top notch on needle
168 main
Air screw 1- 1.75 turns out

Pull the plug. Jet it until the plug is brown turning white. This plug is even a little rich for my liking but will give you a good visual

Results may vary. The stock jetting is actually close to perfect for me, even at 3,000-4,500 feet. If I put a 168 main in my bike I would fully expect it to seize within 5 laps. I actually have a 180 main in right now for the cold Arizona winter.
T-MAC
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T-MAC 12/10/2015 4:46pm
12/10/2015 4:46pm
Any updates on this? My YZ also falls a little more flat than I feel like it should so I'm curious to see what your results were. I just removed an 11oz FWW and will try it out this weekend. I found myself clutching coming out of corners so felt maybe that's counter productive to the FWW. I have been swapping between the stock pipe and an fmf as well, both paired with an fmf shorty silencer. I felt the stock pipe revved/pulled better on top which is opposite of what I hear from everyone else.I'm also playing with different fuels. I tried leaded 110 and that's the fuel the bike felt the most flat on top with. Is this due to jetting differences needed with high octane fuel?
ehr400
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ehr400 12/10/2015 5:20pm
12/10/2015 5:20pm
Most importantly check the timing on it. The 2005-2009's seemed to have varying timing from factory and can mislead you with jetting. There is a good thread on thumper talk. I had one bike with -1 degree from the factory and one with +2 degrees, that one always pinged and surged until I checked it

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