Starting an AF conversion with 86 motor. Some questions

[Kaw391]

Been reading for a couple days trying to figure out all the differences in the engines over the years.  Building a AF conversion with a 2006 KX 250F.  What's the best carb to use if not the stocker?
I'm into this now as a full engine rebuild. I have the cases split now and ordering all new bearings.  Gonna have the crank rebuilt and balanced. Cylinder has scoring so have to recoat it. 

[dave916]

39 pwk standard carb from 88on, depends on what kind of power you want

 The 86 has a very small exhaust port{ good for low down power} if you are looking for topend power it would be a good idea to widen the exhaust port before you recoat it

[motopunk]

39 pwk standard carb from 88on, depends on what kind of power you want

 The 86 has a very small exhaust port{ good for low down power} if you are looking for topend power it would be a good idea to widen the exhaust port before you recoat it

i use also the 86-engine in my ´93 kx500sf .. the ´86-standard-carb was the 40mm mikuni-roundslide .
88- 2004 came the keihin-pwk 39 and some guys updated the k5 with the pwk 41 for more topend power .

watch out before you go on to widening the exhaust port is one question, where will you ride the bike? for mx-tracks is this cylinder perfekt without any exhaust-mods. 

[Kaw391]

Sweet. So sounds like I should be set. Yes this will be mx, maybe an occasional GP and general play riding. I've got a new ktm 450 that I ride, so this will be a toy.  I have used Eric Gorr on my son's Yz 144 and pw 50 so thinking the cylinder is headed to him as we'll. He also said he can put a decompression plug into the head.

[motopunk]

decompression valve is always a good mod for the 500cc engines. ...
 in the main time i ride 250 but for practice and playriding i use 500 . i like this bear power.maybe i race it later the year. but on the most tracks here is this bike just to big..