Jetting Problem

[racerdad33]

My son has a 2002 yz 125 and now has a new cylinder on it with a complete new top end w/stock piston, rings and so on.We installed a v-force reed valve when we rebuilt also.it has a pro-circuit works pipe and shorty silencer.Problem is before we rebuilt it had ran for a year and a half fine then one race blowed.Right before it blowed I noticed we were losing coolant and the bike seemed to run hotter than usual.Now I am really concentrating on jetting a lot.We run Turbo Blue fuel w/ klotz super techniplate oil @ 32-1.Been that way ever since he got the bike.Problem is now we are up to a 490 main with needle clip in the fourth position which is one step from all the way out of main jet.Bike cranks and runs good except when you get it warmed up and let engine idle down to almost dying and hit the throttle hard it will bog for a sec.I f you choke it it will not do that.Next jet size jumps in 20 increments.in other words next jet will be 510,530,etc.Installed a drilled out main jet and it still did it.Help!!! I am just not sure what the next step will be.

 

[atc3434`]

Down at low throttle, you need to increase your pilot side. Your main isn't doing much at such a low rpm, most of your fuel is coming through the pilot till the RPMs come up a little. I'd pull the next size pilot, and see how that goes. Also, at a low idle, if your jetted so your not too rich on the bottom, you probalby will have a slight bog. Thats the way I've settled with mine. I'll trade that slight bog from a dead slow idle for not having touble fouling plugs.

 

[RM_guy]

atc is right about your problem being lean in the low speed circuit. You might be able to adjust it with the air screw if it's not too bad. Turning the air screw out will richen it up. If you have to turn it out more than 2 turns then try a the next size smaller pilot jet.

 

[yam 3]

Originally posted by RM_guy
Turning the air screw out will richen it up. If you have to turn it out more than 2 turns then try a the next size smaller pilot jet.

Out???? Richer???
I thought the opposite
please clear up my confused mind

 

[Eddy V]

Turning the air screw out means more air and the same amount of fuel wich means leaner mixture.More than two turns out tells you to use a smaller pilot.

 

[RM_guy]

Oops!!! :confused:
You guys are right. Turning the airscrew out on a 2 stroke leans out the circuit. On a 4 stroke it richens the it.

You need to turn the screw in. Less than 3/4 turn indicates you need a leaner pilot jet.

 

[jmics19067]

Originally posted by RM_guy
Oops!!! :confused:
You guys are right. Turning the airscrew out on a 2 stroke leans out the circuit. On a 4 stroke it richens the it.

You need to turn the screw in. Less than 3/4 turn indicates you need a leaner pilot jet.

dang dude you need some coffee ! wouldn't turning the air screw in too much to richen it recquire a richer pilot?

 

[RM_guy]

I give up. :(

 

[atc3434`]

So he's saying, basically, your turn in the air screw to richen the mixture. If you get it in to being less that a turn from all the way in, you want to go with a bigger pilot jet, hence a richer pilot. :) I agree, you need to hit the coffee today RMguy.

 

[bclapham]

Originally posted by racerdad33
We installed a v-force reed valve when we rebuilt also.it has a pro-circuit works pipe and shorty silencer.Problem is before we rebuilt it had ran for a year and a half fine then one race blowed.Right before it blowed I noticed we were losing coolant and the bike seemed to run hotter than usual.

Did the vforce requite cutting the carb manifold? if you have got a funky lean condition, check for an air leak.

for what its worth, ive got the vforce on my rm and i am having to lean the pilot so far its rediculous- not uncommon for vforced bikes to require 3 sizes leaner on the pilot! :eek:

 

[RM_guy]

Originally posted by bclapham
...for what its worth, ive got the vforce on my rm and i am having to lean the pilot so far its rediculous- not uncommon for vforced bikes to require 3 sizes leaner on the pilot! :eek:

I went from a 45 to a 40 on the pilot and may try one step lower on my '01 RM250 with the V-Force reeds.

 

[jmics19067]

coool you going to try this weekend? heheh care to show me your trick with the air screw all the way in for a leaner jet :p

seriously though since jetting accurately is new to me I would like some opinions and CONSTRUCTIVE :confused: critisism to make it less of a chore

 

[RM_guy]

Yeah, we'll set your bike up reeeal good, promise:p