looking to increase bottom end

njkx

Member
Joined
Apr 13, 2004
Messages
209
Likes
1
#1
the bike is a 05 YZ 250f. Lately is seems that there is a lack of bottom end power. It could be the performance of the bike or it could be that I have become more comfortable and more skilled with it over time. In any case I am looking to increase bottom end power. Everything is stock on the bike now except I went up 1 tooth on the rear sprocket (49).

Is an $800 investment in an aftermarket exhaust worth it? What are some other suggestions?
 

dirt bike dave

Sponsoring Member
Joined
May 3, 2000
Messages
5,349
Likes
3
#2
Are your valves properly adjusted and sealing properly? How about the piston and rings? Any loss of compression past a leaky valve, worn piston or loose rings will hurt bottom end power.

I would verify your compression, and make sure that the valve train and piston/rings are in good shape before spending money to 'upgrade' the exhaust.
 

njkx

Member
Joined
Apr 13, 2004
Messages
209
Likes
1
#3
valves were checked and in spec....but maybe 10-15 hours on bike since checked...still starts 1st or 2nd kick if that means anything.
 
Joined
Jan 3, 2007
Messages
1,860
Likes
0
#5
I think a Hot Cams stage one will increase the bottom end power for far less money then an exhaust system. You could try your hand at a JD jetting kit for more bottom end as well as a boyseen quick shot.
 

Rich Rohrich

Moderator / BioHazard
Joined
Jul 27, 1999
Messages
22,739
Likes
544
Location
Chicago
#7
njkx said:
What are some other suggestions?
How often are you replacing the piston and rings?
 

njkx

Member
Joined
Apr 13, 2004
Messages
209
Likes
1
#8
Rich Rohrich said:
How often are you replacing the piston and rings?

Ahhh, well...uuhhmm, never. At least I am honest.

approx 50 hours total on the bike.
 

Rich Rohrich

Moderator / BioHazard
Joined
Jul 27, 1999
Messages
22,739
Likes
544
Location
Chicago
#10
njkx said:
Ahhh, well...uuhhmm, never. At least I am honest.

approx 50 hours total on the bike.
That's where your bottom end power wandered off to. ;)
 

150rguy

I got fat bars!
Member
Joined
Dec 21, 2006
Messages
655
Likes
0
#11
I might be wrong, but doesn't the smaller rear sprocket give it less bottom end and more top?
 
Joined
Apr 13, 2004
Messages
209
Likes
1
#13
thanks for all your help..gonna have a friend do the top end. Maybe a high-comp. piston. I have a feeling that will be all I need.
 
Joined
Apr 13, 2004
Messages
209
Likes
1
#14
Any suggestion on compression ratio for this bike? Also manufacturer? CP, JE and Wiseco seem to be the most popular.