more midrange needed on 2007 250

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phil-coley

Member
Dec 9, 2006
7
0
i have a well sorted 2007 yz 250 but need more midrange power, my bike has std exhaust,power core2 silencer,9oz gytr flywheel,powerblade,boyesen radvalve,shaved head to 050 and tidied all the std ports,i run 14/48 gearing and ride enduros std carb with 185 main,45 pilot n3ew needle on clip5 the ignition is set as std. any advice on how to pep up the midrange would be appreciated and does anybody use a quicker action throttle on their 250. philip coley
 
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Matt90GT

Member
May 3, 2002
1,517
1
go back to stock flywheel and run the Vforce reeds. Then double check your jetting.
 

whenfoxforks-ruled

Old MX Racer
~SPONSOR~
Oct 19, 2006
8,129
2
Merrillville,Indiana
Depending exactly how "tidied up" the cylinder is, you may never get that mid-range back. Was the power valve altered? Where did you get the head cutting specs from? Vintage Bob
 
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OriginalRider

Member
Nov 23, 2008
124
0
def get a fmf gold series you'll see a pretty sweet diff in your mid but vforces are want you want.my suggestions are to get fmf gold series,twin air filter,vforce reeds..Flywheel what i was told allow helps either the speed top end or the bottom end.
 

Pete Payne

MX-Tech Suspension Agent
Nov 3, 2000
933
38
.050" is alot off of the yz250 head. Did you do any reshapping of the dome or narrow the squishband? If not your squish velocity is probably WAY high.

I would loose the flywheel weight.
 
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phil-coley

Member
Dec 9, 2006
7
0
more midrange

i dropped my squish down from 078 to 050 which i read was good for a late yz 250 i didnt change the size or shape of my combustion chamber and forgot to measure the ccs of the head after modifying, do you have any info on what is best as i plan on changing the rings in the next couple of weeks.philip
 

Pete Payne

MX-Tech Suspension Agent
Nov 3, 2000
933
38
OK I missread that you took off .028" and now have a squish clearance of .050" (1.27mm) That is a good squish clearance . But you should measure the trapped volume -- I am pretty sure you will be up into the race fuel only zone.
 
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wayfastwilly

Member
Dec 29, 2005
45
0
Eric gorr forward motion racing

contact eric gorr, he ported my 01 rm265 with his "4 stroke" port job and its awsome. He said he could put the power anywhere i wanted it and as much as i wanted. I watched my kid take the inside line on a faster rider on a kx450f, and come out behind and pulled ahead 2 bike lengths on him down the deep sand straight. when asked what happened, the 4 stroke rider said, "I had it pinned, he just seemed to have more power." :) I was very pleased. Wayfastwilly
 

whenfoxforks-ruled

Old MX Racer
~SPONSOR~
Oct 19, 2006
8,129
2
Merrillville,Indiana
jcroley said:
Eric Gorr is the man, best around, a miracle worker!
Click to expand...
No miracle worker! Just plain proven facts. Its the guys who have done it a thousand times, that does fast Johnny's bike, that makes it look real pretty, you need to watch out. Doing your own mods is fine. The likely hood that you or anyone else will find a miracle mod? Not likely at all. You can get all the facts that Eric uses, Virtual software and the SAE archives has every bit of information. Good luck with the talent and tooling part though. I take the easy road, send it to Eric. Pete Payne comes highly recommended also. After that, look out! Bye bye wallet, and ever being able to jet the engine easily. Vintage Bob
 

BSWIFT

Sponsoring Member
N. Texas SP
LIFETIME SPONSOR
Nov 25, 1999
7,926
43
I'll echo Eric's recommendation. I went to a 11 oz FWW because of too much mid-range on my 05 stock YZ. Hope you find what your looking for. I've read a lot about a torque ring spacer, cheap, easy to try, and disgard if you don't find it useful. I have not tried it and I'm not advocating it but for little effort and cost its worth a few minutes of time.
 
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