So I may get a little better performance if I increase the main jet to a 128 with my current foam filter; I guess it is worth a try just to see.

Are you saying that an unplugged 300 exhaust is the same noise level as a Big Gun exhaust? With such a small motor I agree that the header i.d. size makes little difference. If I ever install a big bore kit, I think a better header would be a 'must' to get all the performance out of the motor.

Thanks for your input!

 

I went ahead and installed a 128 main and clip 2nd down tonight. I noticed 'Chris from Winston Salem' on here is within an hour from me and maybe a few hundred feed in elevation. He had good performance with this jetting so I will give it a try.

I found a carb vent plug was missing tonight; this may have been the cause of the decel popping and funny idle. I should have plugged it and ridden it but had the bike apart and the time to rejet it, so tomorrow I will find out how it runs.

 

carb vent plug? 2 vent hoses off the body of the carb should be open, 1 hose off the float bowl (overflow and drain hose) should be open too

yes big gun had a multi tube quiet insert that you could remove for freer flow. With it in db was about the same as 300 can with baffle tip installed. (louder than the 250 cans peashooter). Both pipes uncorked were pretty close, big gun a little louder. I noted it because can usually tell by how louder a pipe is, how many steps up on the main.

 

I'm glad you mentioned this because on my test run this morning I noticed it seems louder. I did not realize larger jets would do this.

The capped port/vent is on top of the carb, towards the front tire. The Dirt Surfer smog removal post shows it needing to be capped after removal of the smog.

The bike is running great again; just in time for my vacation starting at 5:00 today! No more excessive decel popping or slow return to idle. The increase from 124 to 128 main jet seems to have helped the mid-top end power, but I have lost a little bottom end. I assume it has more to do with the clip placement than the larger main jet? The throttle picks up good and smooth, no stumble or hesitation. I hoping when I put the 13t spk on that some of the bottom end will return.

 

Took the week off last week and rode several hundred miles. I'm still happy with the current jetting. I installed pro-taper bars, zeta bark busters and shields. The bars are CR Hi bend and there were no issues with cable length. They feel very comfortable. Also installed the 13th sprocket and a 4.10 X 18 rear tire. I really like the smaller sprocket; mpg dropped from 66 to 64mpg with the change. The 4.10 looks small on the bike but hooks up great on dirt/gravel roads and the little 250 motor seems to like it better than the 4.50 that was on it.

 

After several rides the bike is collecting a little black exhaust on the back of the bike so the 128 main jet must be a little too rich. I am still happy with the performance and gas mileage is good; 68mpg road, low 60'ish dirt roads.
What are my options for final jet tweaking? It has a foam filter, would a K&N help lean it out. How about the backfire screen, would removing it help lean it a bit? Or should I just pull the carb again and drop back to the 124 main jet with clip 3rd from top?

Thanks!

 

Dropped back to the 124 main jet with the clip 3rd down; bike seems to have a little more bottom end feel this way. Next I will start covering the air box to richen as needed.

 

Good. Keep us apprised.

 

no, didn't mean main jet size effects sound

meant pipes that are about the same db level usually jet about the same. And ones that are significantly louder need more fuel.