2021 CSC SG250 Carb Jetting
 

I recently bought a like new 2021 SG250. The prior owner decided riding wasn't for him after 14 miles and then let the bike sit up in his garage for 2 years before deciding to sell it. I've replaced the battery, starter relay, and thoroughly cleaned the carb. It fired right up and runs well. Obviously, I'm still in the break in period and trying to take it easy.

The bike is totally stock and I intend to keep the stock air box and exhaust for now. The stock jets are a 38 and 108. Not terribly small/lean and the 38 seems perfect (more on that below).

I bought the jet kit from CSC that includes a 40 pilot, a 112 and 115 main, and a slotted air/fuel mix screw. I have installed the air/fuel mix screw, but I didn't change the jets while I was in there. I want to get it broken in more before rejetting.

The stock carb and 38 pilot came set with the unadjustable air/fuel mix screw completely seated (leanest). Now that's precision and not leaving any room for error!! When I installed the adjustable air/fuel mix screw, I did open it about 1/2 turn richer. It's good. I like it. I'm at sea level in generally hot and humid Houston.

As stock, I see no need to change the 38 pilot to a 40. I'm happy with it. If I did, I'd probably need to completely seat the air/fuel mix screw if I'm lucky. The 38 seems perfect.

So, when the day comes.... Can anyone share experience on installing a larger main jet (110, 112, 115, 120)? I know these 230cc engines are common in a lot of different bikes and I've read a lot of different jetting 'advice' on TT250 (same as SG250), Hawks, TBR7s, etc. However, much of it done in conjunction with other mods (cone filters, more open exhausts, porting, etc). I don't think the 108 is terribly undersized/lean for stock, but I wouldn't mind a little more top end if available and a cooler running motor.

I can tinker and play, and try the 112 that I have in hand. But would like to hear from those in the know and actual experience. Thanks.

When I bought my first China bike, the Bashan Brozz from Peace sports, it came with a stock jetting of 38/108 also and I believe it ran pretty good too. If you don’t plan on doing any modifications and are happy with the way that it runs then I wouldn’t change anything if it were me. A 112 main may be beneficial to a small degree especially if it’s a tad lean. The main jet and needle play together so to a small degree you will flow a tiny bit more gas with the larger main from 1/4-3/4 throttle but the most change would be from 3/4 to full throttle where the main jet is taking over. Will the 112 main give you more top end? It would be so small that you may not even notice a difference. If at some point you want to make real gains then a new exhaust, better air flow and jetting would be required. Good luck with it, and have fun!!