36mm or 38mm ??
 

All right "experts" Here's one for ya, How do I tell what carb is on my '10 300. Is it a 36mm or a 38mm. And which one works better? Thanks!

Not an expert or even close.

If your 2010 came with the PWK ASII it will have a smaller bowl than the older models and a flat metal cap which is held down by 2 screws. On the top of this cap will be a circle with a number printed in it. 36/38.

If its the older style with the screw cap odds are it is a 38mm. Not sure if anyone reported 36mms sneaking through with these. Think it was more a 2011 thing actually.

The KTMs use 36mms so you can get it to work for you. It will flow better at lower velocities. Smaller openings. Will sign off a bit up top. The opposite for a 38mm. Ideally you'd want an oval bore to get the best of both worlds. Thats what I'd be doing if I had a 36mm.

The pwk as11 is also known as pwm and looks like this

http://www.keihin-us.com/am/products/pwm.php

If you have it on a 300, consider yourself lucky believe it or not, it adds punch and as jakobi says, get it oval bored to 39 mm or get your squish corrected and it has plenty of top end, infact if your in the us, get the rb head mod before you do anything as its the cheapest mod and it will prolly be enough unless you ride desert long haul only!

Big THANKS guys!
It appears as though I have a PWM38 on my bike. So, this is supposed to be a good one? Is there much difference in jetting it?, or is it pretty much the same as any other 38mm GASGAS 300 carb?

Dig through the carburetor sub-forums - there is a wealth of information there. Just beware that the 2011 established a new baseline in jetting, so you'll need to be careful that what you're reading is applicable to your model.

I think you'll find the baseline changes for the 2011 were more of a result of the change away from the screw top capped carb. The new style seem to like much leaner jetting.

My bike is a 2010 EC300 running the same PWK ASII/PWM 38mm. As stated jetting section has many threads, and my findings are about the same as those running the 2011's. Then again my bike was shipped as a 2010 Euro but around the same time as the 2011 EC300 Kicks. Same everything except for headlight and fender. Euro came with Ohlins shock and different valving in the forks.

This may seem like a really silly question, but:
Can the cap stamped with the carb size fit on both the 36 and 38? Is it possible that there are "36's" out there "mistakenly" on 300's that may actually be "38's" with the wrong cap?

I measured my carb body at 38mm and it is stamped 38 on the top cap. So I got one of the "rare" 38's on an '11.

Well, right now I have a #7 slide, N1EF needle, 175 main, 40 pilot.
I just got this thing, so I'm just prepping it and trying to find out what it has before I start to make any changes. I might like it "as is" then again, I might not... Thanks to you guys I can at least look for the right threads!:D

I saw six different '11s, all with 38s.

Yeah the 38mm carbs are far from rare on the 2011's. TBH there are probably more 38mm carbs out there than 36mm ones. It was like Spain ran out of carbs and there was going to be a delay or shortage of 38mm's so they back filled with the 36mm. I can only think of a few people who have reported having 36mm ones, but the thing is if you think you're jetting for a 38 and find out you have a 36 it does make a significant difference so it pays to know which one you have.

I'm think the cap would be interchangable between 36 and 38 but am not certain. I can't see why they would have got mixed up but anythings possible.

Some also have a plastic spacer between the carb reed block (i think.. or air boot?) and others don't. It seems to be an area of variation. I think most 300's came with a #7 slide. Some with the notch, some without. Not sure about the 250s. Then theres the actual reed block spacer aswell.