Hisun Carb Tuning

[SVTKen]

I put an OldMiniBikes Warehouse Stage-2 Kit with a Comet Torque Converter on a Coleman CT200U-EX. The kit comes with a Non-EPA carb and a .037 main jet.

It’s my understanding that the stock jetting is a .028 main and a .016 low speed. I did some searching and I don’t see a lot of info on carb tuning.

I was wondering if it would be smarter to go to something like a .020 low speed and try a .035 main. Adding fuel on the bottom should increase throttle response and taking a bit out on the top should should just balance the bigger low speed.

I also noticed that the exhaust pipe inlet shape was far from ideal so I reshaped it the best I could without compromising the weld.

 

[toomanytoys]

Im running a .20 pilot and a 37 main jet in my tillotson with a header and intake.

but jetting is dependent on elevation. I’m right around a 1000’

the pilot jet increase got rid of my off idle to half throttle stumble. I didn’t mess with the main jet much. Threw in the 37 and my plug color was perfect. I ran it.

 

[SVTKen]

Im running a .20 pilot and a 37 main jet in my tillotson with a header and intake.

but jetting is dependent on elevation. I’m right around a 1000’

the pilot jet increase got rid of my off idle to half throttle stumble. I didn’t mess with the main jet much. Threw in the 37 and my plug color was perfect. I ran it.

Excellent information,

I’m just above sea level (150’). Are you running a Tillotson 212?

Based on your results I’m going to grab a .020 pilot the next time I place an order.

 

[toomanytoys]

Excellent information,

I’m just above sea level (150’). Are you running a Tillotson 212?

Based on your results I’m going to grab a .020 pilot the next time I place an order.

Tillotson 212. I ran the exact same jetting in a predator with the same mods.

 

[SAS289]

If you don't have the off idle stumble you shouldn't need to change the pilot jet. You can, but chances are that it may only help with a bit more fuel at a higher RPM which you may not even be getting to.

I have never touched the pilot jet on my 196's. And most guys with stage 1 kits on stock 196's never touch the pilot jet, even after the common 212 swap on these Colemans.

A few weeks ago I found out that there's no real need to be loud with a header on a stage 1 196 when you have a stock 224 muffler. The stock 224 muffler is a performance upgrade on a stock 196. And I used it for "break in" under load on my 224 which has more compression, cam, and carb than my 196's. If you don't want the noise and can find one, get a 224 muffler. It will work with a larger main jet and filter kit.

 

[LIVIT]

Port matching is something, that I think gets overlooked too often. I did the same when I put a Wildcat 223 on my 200U-EX. When I put the stage 1 carb I took off the 196 and put it on my 223, it did not like it. It was running way too rich. I went back too the carb that came with the 223 and it ran great. I did port and polish the 223 and I live in the lowlands of SC near the coast. A new NGK7 plug showed it was still a bit too rich with the stock carb. So I changed it for a NGK6 and that has helped. I think doing the porting, polishing and port matching is why it's running rich. Just made it all work more smoothly. I'm sure that will all change when I do the cam change etc.. My point in all this is, sometimes changing out those jets is not always the best thing to do. Not sure if it was due to my porting or being at sea level. Good luck with your build and Happy Thanksgiving.

 

[SVTKen]

If you don't have the off idle stumble you shouldn't need to change the pilot jet. You can, but chances are that it may only help with a bit more fuel at a higher RPM which you may not even be getting to.

I have never touched the pilot jet on my 196's. And most guys with stage 1 kits on stock 196's never touch the pilot jet, even after the common 212 swap on these Colemans.

A few weeks ago I found out that there's no real need to be loud with a header on a stage 1 196 when you have a stock 224 muffler. The stock 224 muffler is a performance upgrade on a stock 196. And I used it for "break in" under load on my 224 which has more compression, cam, and carb than my 196's. If you don't want the noise and can find one, get a 224 muffler. It will work with a larger main jet and filter kit.

Snow is upon use in the North so tuning will have to wait for nicer weather. My plan will be to have a larger pilot jet on-hand and I’ll start with the main and go from there. I already have an assortment of mains.

Interesting info on the muffler, is it off a Predator 224?

 

[SAS289]

Yes, the stock Predator 224 muffler.

 

[SVTKen]

Port matching is something, that I think gets overlooked too often. I did the same when I put a Wildcat 223 on my 200U-EX. When I put the stage 1 carb I took off the 196 and put it on my 223, it did not like it. It was running way too rich. I went back to the carb that came with the 223 and it ran great. I did port and polish the 223 and I live in the lowlands of SC near the coast. A new NGK7 plug showed it was still a bit too rich with the stock carb. So I changed it for a NGK6 and that has helped. I think doing the porting, polishing and port matching is why it's running rich. Just made it all work more smoothly. I'm sure that will all change when I do the cam change etc.. My point in all this is, sometimes changing out those jets is not always the best thing to do. Not sure if it was due to my porting or being at sea level. Good luck with your build and Happy Thanksgiving.

I’ll make one change at a time on the carb and see what the results are. I’ve done a bit of carb tuning over the years and have learned to make small changes and test the results. At some point I may look for a pipe that is an actual D-port so it will better match the head, definitely want one with a muffler though. Happy Thanksgiving to you too!