KTM carb swap 38/36mm?????

[nom de guerre]

ok... I have a '12 125 with a 38mm PWK and a '13 250 with a 36mm PWK-

I thought about going oval bore, etc on both with a little other work, but I am curious to this swap, especially with the 250. I have read about a couple of guys going with a 38mm on their 250/300's and seem to really like it. Both carbs are identical dimensionally, just the bore is different.

My main questions are... will the bore changes/swap affect the actual jetting that much? Can I just change out the slides/jets/etc.? Then adjust from there if required?

Should I just leave well enough alone? Thanks TSM crew.

[_X_]

sounds like you need to go testing nom.

[2STROKEREVOLUTION]

Just wait for the new APT SmartCarb. Some of those oval bore with intelajets cost more than that new carb will and that carb is shaping up to be sweet. The cast model is supposed to be $350-400.

Your 125 has a bigger carb than your 250? That seems odd. In the mean time, swap carbs and see how your two bikes feel. That could be interesting.

[nom de guerre]

Thanks 2SR... You must be reading my mind, I spent all day reading about the APT carb. I am getting one for sure, can't wait. Yep,the 125 has a bigger carb. The 36 is for low end response I guess on the 250... I think with the swap, I need a larger MJ, 1 pr 2 sizes.

[2STROKEREVOLUTION]

Thanks 2SR... You must be reading my mind, I spent all day reading about the APT carb. I am getting one for sure, can't wait. Yep,the 125 has a bigger carb. The 36 is for low end response I guess on the 250... I think with the swap, I need a larger MJ, 1 pr 2 sizes.

Haha, I spent a long time reading about it too. I am sure you were reading through the GasGas forum talk about it. I want to join just to get those dyno charts, etc. that he posted there. Any other info you saw besides that and their website?

It really seems like a sweet product. It would be perfect for the impossible to jet 380s. And 10% more power? That would be crazy. Auto elevation adjust? Perfect for guys like me who suck at jetting.

I am new to understanding carbs, but a 38mm on a 125? Seems like it wouldn't be able to get any fuel, and get nothing at low revs. If they choose a 36 over a 38 for a 250 to get some bottom end, then a 38 on a 125 sounds like it would be super peaky. I think it would be worth the experiment to swap them and see the results.

[nom de guerre]

Thanks 2SR... You must be reading my mind, I spent all day reading about the APT carb. I am getting one for sure, can't wait. Yep,the 125 has a bigger carb. The 36 is for low end response I guess on the 250... I think with the swap, I need a larger MJ, 1 pr 2 sizes.

Haha, I spent a long time reading about it too. I am sure you were reading through the GasGas forum talk about it. I want to join just to get those dyno charts, etc. that he posted there. Any other info you saw besides that and their website?

It really seems like a sweet product. It would be perfect for the impossible to jet 380s. And 10% more power? That would be crazy. Auto elevation adjust? Perfect for guys like me who suck at jetting.

I am new to understanding carbs, but a 38mm on a 125? Seems like it wouldn't be able to get any fuel, and get nothing at low revs. If they choose a 36 over a 38 for a 250 to get some bottom end, then a 38 on a 125 sounds like it would be super peaky. I think it would be worth the experiment to swap them and see the results.

Yep... Read all that and the site. The Pikes Peak results were impressive... I have been in contact with the original buyer, he LOVES the carb. I will get it, the CNC version. Yeah, it really seems to be legit. I like new stuff and look forward to this.

I bet the 38/40 would rule on the 380...  Yep, big carbs are the norm for small bores... KTMs came with 39mm for a ling time. My Husky 150 had a bored to 39 from 38 and divider plate from RB... Speaking of that, the APT owner says the bored/divider plate carb isnt even close to the Smart Carb...

I will play around with the two, but will have the Smart Carb on the 250 sooner than later.

[SachsGS]

In the late 90's I had a 250 Maico with a 40mm Bing and it had a smooth torquey engine with lots of bottom end. At 8000 + feet the bike still carbureted well.

[2STROKEREVOLUTION]

Thanks 2SR... You must be reading my mind, I spent all day reading about the APT carb. I am getting one for sure, can't wait. Yep,the 125 has a bigger carb. The 36 is for low end response I guess on the 250... I think with the swap, I need a larger MJ, 1 pr 2 sizes.

Haha, I spent a long time reading about it too. I am sure you were reading through the GasGas forum talk about it. I want to join just to get those dyno charts, etc. that he posted there. Any other info you saw besides that and their website?

It really seems like a sweet product. It would be perfect for the impossible to jet 380s. And 10% more power? That would be crazy. Auto elevation adjust? Perfect for guys like me who suck at jetting.

I am new to understanding carbs, but a 38mm on a 125? Seems like it wouldn't be able to get any fuel, and get nothing at low revs. If they choose a 36 over a 38 for a 250 to get some bottom end, then a 38 on a 125 sounds like it would be super peaky. I think it would be worth the experiment to swap them and see the results.

Yep... Read all that and the site. The Pikes Peak results were impressive... I have been in contact with the original buyer, he LOVES the carb. I will get it, the CNC version. Yeah, it really seems to be legit. I like new stuff and look forward to this.

I bet the 38/40 would rule on the 380...  Yep, big carbs are the norm for small bores... KTMs came with 39mm for a ling time. My Husky 150 had a bored to 39 from 38 and divider plate from RB... Speaking of that, the APT owner says the bored/divider plate carb isnt even close to the Smart Carb...

I will play around with the two, but will have the Smart Carb on the 250 sooner than later.

Hopefully I can get the cast carb in a year when I have some more money. I would like to understand what he was saying about the 38-40 taper bore. He said it is good for pro riders. The way he said it earlier though it sounded as though it would provide the bottom end of the 38 with the top end of the 40. Sounds good to me, and the 40 would be more peaky. I'll have to figure that out when I can pull the trigger on it. Damn, life of a student with no money.