38 or 39mm carb for CR 500?

[keen]

I am thinking about trying a 38 or 39mm Keihin PWK carb on my 90' CR 500. Not racing, just hill climbing and such. Any opinions on which size would be better? pro's & cons? Thanx

 

[cujet]

The CR500 likes big carbs when making big power. I have seen some people go to the Mikuni VM44. I even know of 1 person running 2 carbs, 1 of which is case reed!

I prefer the PWK 39mm for the big bores. My gut feeling is that the 39 is just a little small for a 500, but they seem to work very well.

Chris

 

[keen]

I want a better carb than the PJ and there seems to be quite a few 39mm PWK's on e-bay. I am not looking for max power but rather the best power across the board. 1mm doesn't sound like much but I don't want any jetting or power problems. Thanx

 

[Lorin]

I installed a 39.5 mm pwk (standard on the kx-500) on my wr 500 with very little trouble (different throttle cable). That said, I really liked what it did for me on my bike (coming from a round-slide mikuni 38mm VM). Jetting seemed much easier (seperate choke circuit), and jets are easy to find. I didnt notice any loss in the low end power of the bike, but I probably wasnt using it all anyway. I would buy the PWK 39 again in a heartbeat if I was experiencing problems with a stock carb, even on my 250. My bike eventually ended up running stronger, and better all around, mostly due to jetting with the new PWK. If you do buy an aftermarket carb, make sure it is the same width (distance between reed and airbox) as the one that you currently run (they make a few different sizes).