Cr-125 racebike

So I have a 2006 cr125 that I race and I love it! I’ll give a quick list of all different mods

 

Fully rebuild motor trans/bottom/top to full OEM specs.

 

I run 100LL with a 40/1 ratio

 

Vforce3 Reed

 

Pro circuit pipe and shorty silencer

 

JD jetting carburetor

 

So the issue I’m having is when I’m revving the piss out of the bike in 3rd or 4th flying around the track I have almost little “hickups”in the high revs (mostly happens in 3rd gear) it gets me in trouble cause when I’m trying to make a big double coming out of corners in third it will hickup in high revs and slightly cut out...my first initial thought is that it’s starving for air at higher revs. Would simply drilling holes in my air box for more air flow help this? Or is it starving fuel at high revs and I could simply change jets out to fix this? Thanks for any brainstorming!!

Dirty air filter?

Dirty air filter?

No I replace air filter with clean one after every ride. It’s my race bike I take very good care of it and everything is in good condition. Just trying to fine tune the engine now

Personally I would cut out the avgas if you are stock. Or at least 50 50. Whenever I used it my bikes simply didn't run as good. JMO though.

What is avgas?

What is avgas?

Aviation fuel. Used in airplanes. 100 octane LL- mean “low lead”. Has very good lubricating properties which is a bonus for 2 strokes!
6 minutes ago, Caleb99olsen said:


Aviation fuel. Used in airplanes. 100 octane LL- mean “low lead”. Has very good lubricating properties which is a bonus for 2 strokes!

Ok, so fuel with Xtra lube.  Where would you get it?

Ok, so fuel with Xtra lube.  Where would you get it?

An airport haha you have to make sure your engine can take it. My squish tolerance is set up to be able to take the higher octane rating
Personally I would cut out the avgas if you are stock. Or at least 50 50. Whenever I used it my bikes simply didn't run as good. JMO though.

My squish tolerance is set up to handle the higher octane.
Just now, Caleb99olsen said:


An airport haha you have to make sure your engine can take it. My squish tolerance is set up to be able to take the higher octane rating

Haha i see. thanks

I also have a cr125 i have similar problems i hope you figure this out

2 hours ago, Caleb99olsen said:

Would simply drilling holes in my air box for more air flow help this?

Remove one side cover for a few laps. Easy way to see if more air is effective. IIRC, the 02 and 03 CR125 airbox was said to be air restricted so the mod was to switch to the 05+ airbox and air boot. 

So I guess the proper terminology is that the top end is going “flat” and I’m wanting to get more over rev for my bike

Get rid of the shorty and try a full length silencer.

From my limited experiences on my YZ125, a shorty added a bit of 'hit' at the cost of top end & overev.

 

1.  Mix your fuel at 32:1 and stay at that ratio on a 125 engine. Make Sure your float is set perfect as well...........

2.  100LL Av Gas is good fuel, especially since it is "Ethanol Free"

3. NEVER use Gasoline with Ethanol in it..Engines hate it, Carbs hate it...My bike will not even run on the Ethanol shit........and you likely have no access to ethanol Free gasoline in  California with the "Reformulated" Gasahol crap....

4. Av Gas has a slightly different specific gravity...You usualy have to play with the jetting a little have it dialed in for Av fuel it should be good to go.

The Specific gravity and distillation curve are similar to Race fuel which means it runs slightly richer than automobile pump gas. Usually one jet size lower and dropping the needle one position will get you close............Tune the carb to run on this fuel and you should be good to go......................

You did the Khein swap from OEM Mikuni calibration and may have to play with leaner or  Richer to get it dialed in though........

 

Edited by Smokin CR 125R

Da fuq? Damn my bike must be completely screwed up then...

1 hour ago, gscx said:

Da fuq? Damn my bike must be completely screwed up then...

Ethanol. Rotella. No-Toil. The three sacred cows of TT. 

1.  Mix your fuel at 32:1 and stay at that ratio on a 125 engine. Make Sure your float is set perfect as well...........
2.  100LL Av Gas is good fuel, especially since it is "Ethanol Free"
3. NEVER use Gasoline with Ethanol in it..Engines hate it, Carbs hate it...My bike will not even run on the Ethanol shit........and you likely have no access to ethanol Free gasoline in  California with the "Reformulated" Gasahol crap....
4. Av Gas has a slightly different specific gravity...You usualy have to play with the jetting a little have it dialed in for Av fuel it should be good to go.
The Specific gravity and distillation curve are similar to Race fuel which means it runs slightly richer than typical pump gas. Usually one jet size lower and dropping the needle one position does the trick on............Tune the carb to run on this fuel and you should be good to go......................
You did the Khein swap from OEM Mikuni calibration and may have to play with leaner or  Richer to get it dialed in though........
 

I’ve always ran 40/1 it’s given me plenty of lubrication for my engine and less oil=more power. I know many factory riders that also always have 40/1 in their bikes. Yes you have to rebuild more often but I’m racing it only so it’s expected. And yeah im going to try fine tuning my carb. I’m gonna see if it’s air starving or if it needs more fuel
1 minute ago, Caleb99olsen said:

and less oil=more power

:thinking: 

Factory 125's ran in the 28:1 range, 

it's been dyno proven that more oil helps the ring seal and increases compression

even all the way to 16:1 but at that point the downside is reduced throttle response.

 

Edited by mlatour
Factory 125's ran in the 28:1 range, 
it's been dyno proven that more oil helps the ring seal and increases compression
even all the way to 16:1 but at that point the downside is reduced throttle response.
 

Yeah that’s also on heavily moded motors I’m going off what local motocross trainers like BJ in Southern California. He was a pro for a long time and owns his own motocross school and he recommends to run a 40/1 ration with the specific oil in my motor

40:1 is modest for a high performance engine. you could go 50:1 with a top quality oil.  wacker compactors have a chrome bore and recommend 100:1 mix. a machine built to squash dirt wont be as high performance as a race bike.  IMO take your time, change ONE thing at a time and test small adjustments to see what helps or hinders. being such a narrow window of issue your looking for a very small adjustment to fix said issue and not effect the rest of the operating range. try adjusting the slide needle and or main jet and see what happens. good luck with it I hope you get to chase some chooks soon.:ride:

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now