VP C-12 in CR125

[Durt Cycler]

I am currently running Sunoco 94 pump with Motul 800 @ 50:1 and my dirtbike shop I go to just got some 5 gallon drums of VP C-12 race fuel. I am gonna try it since people on here are using it with good results. My question is would I have to do any special things to my jetting, sparkplug type, or premix ratio? Would mixing a 50/50 blend of C-12 and Sunoco 94 do any good? BTW what kidn of improvement can I notice from C-12 from regular 94 pump gas? Thanks for any input...:D

 

[KawieKX125]

Unles you can jet a bike perfectly, there is really no need to use it for your application. It will improve throttle response but I notice no actual power gains between C-12 and pump. MR-2 is a different story. It will impove power.
Unless you bike is detonating on pump gas, I would stay with it.
Spend your money on extr oil, because 50:1 is really lean for a 125. I would never go leaner than 32:1 in a 125.:)

 

[Durt Cycler]

Oh for sure Kawie that fuel ain't going in my bike untill I get this jetting set right. I will go back to 32:1 when I don't get enormance amounts of spooge all over my rear fender and swingarm. But if you or anybody else can help me with my jetting here goes.

STOCK JETTING
172 main
58 pilot
R1469N needle
3rd clip position
2 turns out on air screw
NGK BR9EG plug

CURRENT JETTING
170 main
55 pilot
R1470N needle
3rd clip position
2 1/8 turns out on air screw
NGK B9ES plug

With a new plug my bike will rev perfect and run fine for a few hours ( when I'm on the gas alot ) but then you will feel my bike starting to serge and bog out on 3/4 - WOT so it leaves me thinking I am running lean on the top. My bike will foul the stock BR9EG plug faster then a BR9ES but the B9ES seem to last longer. I look at the fouled plugs and it seems to be the right heat range ( first 3 threads are black ). I tried a BR8ES and it serges bad when I get on the gas. My plug is not wet fouled it is black but not wet when it gets fouled. I am stumped. I and running motul 800 @ 50:1. Some please help me! :scream: Also FMF recommends using a 55 pilot and R1468N needle and Boyesen recommends going down 1-3 on the main...

Also my Alttitude and temp. is 500FT and 40-55 degrees F
So my correction factor is .96 ( 172 x .96 = 165...58 x .96 = 56 )

 

[Durt Cycler]

Also what's weird is my bike will run perfect untill you can't hit the powerband in 1st or 2nd gear and it feels like it surges and bogs untill you hit 3rd gear then it runs fine and flys :eek:

 

[KawieKX125]

Go to a 32:1 ratio then get the jetting dialed with pump gas. It will take a while. Visit the jetting guides at www.eric-gorr.com for help.
Then if you decide that you need to spend your money on C-12(I dont think you do) then you will need to rejet again as the jetting will be different between pump and race fuel.

 

[scotts250]

C-12

Not really necessary unless your have cylinder/head work that would cause higher compression. Does improve throttle response and smells good when it burns though!
I run it 50/50 with 93 pump gas in my '01 CR250 cause it's jetted kinda agressive and when it gets hot outside it like to ping a little. My'94 is not jetted on the lean side and does seem to have more consistent throttle hit on pure C-12 mixed 32:1 but not as noticeable on the 50/50 mix at 32:1.

 

[Durt Cycler]

Well from what I know the cylinder is ported & polished, but I am not sure is the cyl. has been bored over or the head has been milled but I am gonna take the head off tommorow to check what size piston it has and clean the oil buildup on my piston tope and head. BTW it is getting a Vertex race piston which claims it has to run off race gas.

 

[KawieKX125]

As I said above, unless your bike detonates with pump gas and good jetting, you have no need for race gas, save your money.

 

[Mr. Clean]

If you are wide open when your bikes stumbles until you hit third gear,I am certain that your main jet is about two sizes too large. Two strokes will run ok slightly rich if under a big load and will stumble as you described under light load. This is manifested on your bike by stumbling in first and second gears(light load)and smooths out under higher loads in the higher gears. To prove my theory, hold your bike wide open in third gear for several seconds longer than normal and you will notice the same thing with a little less stumbling.

Kurt yz 250