1991 KDX no idle

Joined
May 31, 2001
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#1
I have a 1991 KDX200 that has a new top end, pipe mod per Canadian Dave, boysen reeds, air box mods, FMF silencer/spark arrestor and it seems to want to run only at half to full throttle. I cannot get idle or the enriching circut to work. The air screw and idle screw have no effect on the motor and I am seeing bubbles in the coolant tank when I rev it. I have tried several jet/needle combos including 155 main, 48 pilot and the needle clip moved down 1 from center. In this setup it would run at 1/4 to full throttle although it seemed a little down on power overall. There don't seem to be any air leaks around the carb and the reeds are new. I have taken the pipe off and the power valve is in time and clean. I should mention here that the cylinder was sleeved and a stock piston fit by Wiseco last summer. I am starting to think that I have a cracked head or bad headgasket. Any ideas what else to look for as I tear this thing apart one moe time?
 
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Apr 18, 2001
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#2
try a 155 main,45 pilot, stock needle with clip in second spot from the top, and air screw 1 and 3/4 turns out. that should help
 

Canadian Dave

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#3
“ I am seeing bubbles in the coolant tank when I rev it.” Sounds like a potential head gasket issue here. I wouldn’t even think about trying to solve your ill jetting issues until you insure you aren’t leaking coolant into the cylinder, well unless you really enjoyed your last top end rebuild ;)

For the time and minimal cost I’d just replace the head gasket and torque it to factory specs using the proper torque pattern. Remember to check the torque valves again after riding the bike a couple times.

After you’re confident there isn’t a potential head gasket issue try a 155 main, move you jet needle’s clip to the second from the top position, and try a 45 pilot. Fine-tune the pilot circuit using the airscrew. Be sure to check you main jet to insure you aren’t running lean by doing a plug reading at WOT. Check out the carb tuning section on the JustKDX home page for more details.

David
 
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May 31, 2001
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#4
I will try the carb recomendations when I get the cylinder and piston back from Wiseco. I tore the top end down and found that the piston had been installed reversed, the result being severe scoring at the exhaust side. My luck with KDX cylinders has apparently run out this week.