Author Topic: Starting an AF conversion with 86 motor. Some questions  (Read 3308 times)

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Offline Kaw391

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Starting an AF conversion with 86 motor. Some questions
« on: June 11, 2013, 06:25:23 AM »
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. 

Offline dave916

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Re: Starting an AF conversion with 86 motor. Some questions
« Reply #1 on: June 14, 2013, 02:25:38 AM »
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

Offline motopunk

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Re: Starting an AF conversion with 86 motor. Some questions
« Reply #2 on: June 14, 2013, 10:02:33 PM »
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.  8-)
big 2 stroke bikes are weapons for real men, who don´t fear death or devil. ;O)
´83 kx250, ´87 kx250 (with 360 big bore), 87 kx500, ´93 kx500 sfc

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Offline Kaw391

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Re: Starting an AF conversion with 86 motor. Some questions
« Reply #3 on: June 16, 2013, 02:46:04 PM »
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.

Offline motopunk

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Re: Starting an AF conversion with 86 motor. Some questions
« Reply #4 on: June 16, 2013, 04:28:55 PM »
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..
big 2 stroke bikes are weapons for real men, who don´t fear death or devil. ;O)
´83 kx250, ´87 kx250 (with 360 big bore), 87 kx500, ´93 kx500 sfc

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