Honda Spree and Elite 50 Forums

I have a Honda Helix CN250 I picked up for a good deal 600.00 it needed a new top end.Now I have the top end all done I bored it 1mm over to 73mm making it a 251cc I know I need to up the jet size but no shop will help because California smog laws The stock carb is a 30mm Keihin the jets are 38 slow jet and 110 main jet. The help Im looking for is what size jet to start off with I know the 110 is to lean. I also changed the stock muffler to the muffler of a YY250T jonway here a pic I had to cut and weld the down pipe to make it fit.Any help will be appreciated.
Here a short video of it running. http://youtu.be/4PfdbW5HtDo

Here is a good starting point from Randy P. http://www.ch250.net/techtips/4.htm

Johnniespeed wrote:Here is a good starting point from Randy P. http://www.ch250.net/techtips/4.htm

I have read over the whole site he talks about whats good performance upgrades for the stock motor but nothing about motor that has been bored over There's got to be someone out there that has done this in the past. You spree guys know when you bore your motor this changes things like jetting and reeds etc need to be upgraded. Im just trying to find a good base line to start at for I don't have to buy half a dozen jets to get it right.

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On my ch250, I'm running 0.50 mm overbore and using stock main jet, runs perfect, plug looks good, I did go fatter on the pilot jet so the mixture screw didn't have to be out so many turns.
I agree with LMH, four stroke tuning is different from two stroke tuning.
Let us know what you end up using, once you get yours dialed in.
My guess is that the non-stock exhaust would have a greater effect on jetting than the overbore, and even then I think the effect is small, since this is four stroke.

I know its a little late Thanks for your guys help. This is what I have done since I've been gone I rebuilt the carburetor I changed the slow jet to 42 and the main jet to 120 I also drilling out the vacuum port hole on the bottom of the throttle slide to 1/8".The last owner broke off the top part of the stock pilot jet screw and that was fun to get out of the carburetor. I'm also still waiting for the pilot jet tool and mini tack for I can start tuning the pilot jet screw Honda put that dam screw in a stupid spot need a special tool to get to it because my hands are to big


California Epa Carburetor

Old pilot screw and new pilot screw

float height at 18.5mm / 0.73in

New float and new Keihin slow 42slow jet & 120 main. I got my Keihin jets from jets R us http://www.jetsrus.com/a_jet_kit_scoote ... _helix.htm