125-200cc Why the big carb on the WR125?

Back when I used to race a TRX250R atv, it worked best in the woods with a 35mm carb. I tried a 38mm on it and it lost bottom end power and throttle response. I would think that the effects of the big carb would be even worse on a 125cc 2 stroke motor - why not run something along the lines of a 34mm (or even smaller) carb??

I think there are a number of guys that switched to a 36mm carb and really liked the better response and bottom/mid power. Of course they were switching from the finiky TMX to a PWK. My personal opinion is that when you have a carb that works as well as an airstriker PWK 38 why make the smaller carb compromise? JMHO

Walt

I am leaning towards the 36mm PWK. Maybe the Motorsportz - has or can test them as a comparison . They are selling them and the 38mm. "NWrider" has a 36mm and likes it .
I for one would sacriifice small amount of top end for more linear torque curve and better response.

How do you go pulling from a start on hills Walt ? ( even though you have a 144)
I dont get enough torque to re-gather momentum

I have to say that I am amazed at the level of torque my 144 is making currently. I was stopped on a number of steep hills today and was able to tractor off and pull the hill on the bottom end. I am going to gear mine back up to stock 13x50 as 1st is awful low when it pulls this hard. It also will easily climb up onto the pipe if you are somewhere you can fly. I was rarely in 1st in some tight steep stuff using 2nd almost exclusively for climbing around the trees and in the snow. I was finding myself in 3rd and 4th on slow hills just chugging away. The PWK airstriker is really an awsome carb for bottom and mid. The JD jetting kit is spot on and just works.

Thanks Kelly and Motosportz for the good deal and great service.
Walt

I went with the 36 first and eventually ended up with the 38 because I missed the top end scream and rev, granted I also ended up with an RB designs divider plate(permanent powernow). Here is a comparison thread I did a while back.

http://www.thumpertalk.com/forum/showthread.php?t=630538

Did you get more top end with the 38? I have a 36 and it will chug very well. But It does not rev as far as I think it should but I also have the compression raised and the timing advanced a hair which could make a difference. I would really like to test both back to back.

For what the OP said, the TRX is an old school motor without a power valve so they had to get low end other ways. Small bores generally have larger carbs because they need to rev to make power. Many MX 125 models come with 39mm carbs.

More top end than the 36, definitely, more top than the TMX?...hard to say. I do feel the 38 with the RB divider plate is the ticket, stronger throughout the range.

I have since thrown the TMX back on due to the PWK needing rebuilt, and the PWK is definitely better, bike has a weaker low end and midrange with the TMX.