[DieselB59]

Okay, here goes. Maybe someone out there can help me with this one. I went out with my 450R today and did some riding. First time out with the Yoshimura exhaust. The day went great, until just before I was going to put it onto the truck. Just pulled off the track, and it stalled on me as I downshifted. Thought nothing of it, and restarted it. Ran fine, until I tried to just touch the thumb throttle, then stalled. Checked gas, plenty in tank. Was quite a distance from the truck, so I tried some more. Noticed that it will not stall if I slowly bring the revs up just a bit, then give it anything from about 3/4 throttle to WOT. Limped it back to the truck in 1st gear, but it was not running right at all. Breaking up and popping and stuff. When it shuts off, it's almost like it's running out of fuel. But it's not. Took the carb off, checked the bowl, and the main and pilot jets, and cleaned them all while I was in there. Does not make it any better. Tried taking the fuel cap off to eliminate vapor lock, but still stalls. Tried tank petcock at all positions and problem still remains. A member of the track I was riding at asked if it has a Throttle Position Sensor, said maybe that is it. I don't know if it has the control to do this or not.
Here's what I have done to it.
Yoshimura Stainless Exhaust Full System
Uni Filter with lid off
DynoJet jetting kit with their needle installed and 175 main jet (per DynoJet instructions with exhaust and no lid), Air/Fuel screw 2-1/2 turns out.
Note, it ran fine all day long and idles okay
Stalling problem just occurs off idle.
Spark plug was black/dry carbon on it, but that could be from the poor running condition.
Anyone out there have a shop manual that may troubleshoot this?

 

[DieselB59]

I think I found a big piece of the puzzle I was looking at. Did some research on jetting troubleshooting, and narrowed it down to a needle problem as I cleaned out the main and pilot jets and the bowl, etc. So, I took off the top cover of the carb and found the slide piston jammed about 2/3 of the way open. I knew something wasn't right when I was looking at the carb hanging out, but was too busy running around like an idiot to see the thing wasn't seated through the air inlet. Just took it for granted that I could see the butterfly and put it back together. Anyway. Soaked it in WD40 and ran the throttle linkage from idle to WOT about a thousand times (literally), then sprayed it again, and left it sit overnight. Will reassemble tomorrow and let you all know. I'm 99% sure that's my problem indeed.

 

[DieselB59]

Thanks desert_450r! All went well with the WD40 overnight soak. Today, I cleaned it all up with some Q-Tips and reassembled it with care. Took a couple extra kicks to start it, but I'd assume that's due to the WD40. Cleaned all the dirt and mud off it, and ripped it up and down my yard a few times. Feels good as new! B)