2004 YZ125 Single Track...Need more bottom end power!

Hcallz5
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Hcallz5 1/9/2023 6:23pm
1/9/2023 6:23pm

Thick base gasket and cut the head to compensate.

Get a slide and needle combo to dial in jetting.

Twist the throttle and slip the clutch as needed lol.

By the way the Tusk Emex35 comes in a 100/19 size, been running the 110 on my 350 and it's held up great.

whips
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whips 1/10/2023 1:01am
1/10/2023 1:01am

Built a 08 yz125 up for the wife a couple years ago,ran a 35 pilot to crisp up the 1/4 throttle, needle 2 nd clip,thinner base gasket to improve bottom weaken top,dep pipe, was awesome compared to a stock 125 on the bottom end,maybe just start with the easy mods 

JBoneMotorworks 1/10/2023 4:53am
1/10/2023 4:53am
Hcallz5 wrote:
Thick base gasket and cut the head to compensate. Get a slide and needle combo to dial in jetting. Twist the throttle and slip the clutch...

Thick base gasket and cut the head to compensate.

Get a slide and needle combo to dial in jetting.

Twist the throttle and slip the clutch as needed lol.

By the way the Tusk Emex35 comes in a 100/19 size, been running the 110 on my 350 and it's held up great.

Accelerating the port timing by raising the cylinder will take away low-mid and effective stroke and add upper rpm. 

A thinner base gasket will retard the port timing and add low-mid at the expense of top end.

This is backwards- J

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Mykdee
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Litchfield Park, AZ, USA
Mykdee 1/11/2023 4:30pm
1/11/2023 4:30pm

Installed V force 3 Reed valves, definitely helped. Seem to smooth out the low to mid range and the power came on sooner. Took it out today for about a 30 mile ride and it ran great other than the spooge. I really need to read yet or at least go back to the old style foam filter. I had in it before I installed the UNI filter.

The Shop

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btroxler
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Saltillo, MS, USA
btroxler 1/18/2023 10:05am
1/18/2023 10:05am

Easiest is install a 134 or 144 kit. I, at one time, had a 04 - YZ125 that I installed the 144 kit on it and rode it in the woods and it was the ticket. It is also a reliable kit as well, cylinder, piston, cylinder head and small jetting change.

I chose to use the Athena 144cc kit, because I wanted to retain my stock cylinder etc.

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MxAddic
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MxAddic 1/18/2023 11:57am
1/18/2023 11:57am

MX53/100

Air down from 12 until you get the traction you want.

A lighter tire is free low end.

squabblecreek 1/25/2023 5:57pm
1/25/2023 5:57pm
Mykdee wrote:
Installed V force 3 Reed valves, definitely helped. Seem to smooth out the low to mid range and the power came on sooner. Took it out...

Installed V force 3 Reed valves, definitely helped. Seem to smooth out the low to mid range and the power came on sooner. Took it out today for about a 30 mile ride and it ran great other than the spooge. I really need to read yet or at least go back to the old style foam filter. I had in it before I installed the UNI filter.

Over oiled the air filter?

RK Tek
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Preston, ID, USA
RK Tek 1/26/2023 5:46pm
1/26/2023 5:46pm
Mykdee wrote:
I have a 2004 YZ125, completely rebuilt motor and runs great. Looking to build it into a decent single track bike.  I added a 51 tooth...

I have a 2004 YZ125, completely rebuilt motor and runs great. Looking to build it into a decent single track bike.  I added a 51 tooth rear sprocket, kickstand, Protaper bars, new chain. But need more bottom end power.

I went for a ride at The White Tanks in AZ today. While I was out there I meet a guy and he took me out on some serious Single Track trails, destroyed me! I need more bottom end, ideas? I had a hard time on the steep hills. I know, get a bigger bike, that's not in the budget right now. I was really surprised how well the 125 did, just need a little more bottom end! Ideas of what I could do?

ALSO, what rear tire would be good for rocky, sandy single track. I kind of want to stick with a 19" for weight savings.

Thanks!

It is very easy to gain more bottom end on the YZ 125.

The FWW is a great addition but that doe snot add "engine power" 

If you re-chamber (not shave) the head to a better design, this will increase low end torque considerably.

Also, getting the jetting correct is a big part of the recipe.

The difference with the head, properly modified, and the correct jetting is substantial.

Pit Row

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