06 yz450f hard to start when hot and weird idle

10 replies to this topic
  • kjadair91

Posted March 05, 2016 - 02:25 PM


once my bike gets hot its is so hard to get started. It will bump start just fine. Also i cant get the bike to a consistent idle. ill set the idle blip the throttle and it will sit at a higher rpm and blip it again and it might drop to where it was set or it will stay at the higher rpm. 


I am running a 170 main and a 48 pilot with a NFLR needle at sea level

​valve clearance is in spec 


ive been trying to fix this since i got the bike and cant figure it out. 



  • duck996

Posted March 05, 2016 - 02:30 PM


Make sure pilot is not plugged. Also check out ring seal on slide plate. The only ring was my problem.

  • damnbiker94

Posted March 05, 2016 - 03:45 PM


Hanging idle is often times a lean condition. Check for vacuum leaks, proper adjustment and operation of the hot start, etc. Another common oversight is a poorly adjusted or binding throttle cable.

  • kjadair91

Posted March 05, 2016 - 04:59 PM


I'll pull the carb apart when I get back Monday and inspect everything. I'll probably just order a rebuild kit while I'm at it just to make sure.

  • kjadair91

Posted March 05, 2016 - 05:04 PM


Can anyone point me in the direction of a good rebuild kit for these carbs

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  • Krannie McKranface

Posted March 06, 2016 - 06:37 AM


Hanging idle

Caused by small air leak in one or more places

Very common on carbs that have not been serviced in a while, or that run un-treated pump gas (ethanol contamination)


No rebuild kit for what you need:


- slide plate seal

- fuel screw oring

- needle jet (emulsion tube that ovals)

- hot start plunger, cavity, and cable service (or block off with a choke plunger)


Before anything else, properly adjust the fuel screw for max idle (then lower idle with fuel screw if needed) to see if that helps.

  • grayracer513

Posted March 06, 2016 - 07:38 AM


A hanging idle can also be caused by tight intake valves.  Check your clearances.

  • kjadair91

Posted March 06, 2016 - 11:40 PM


pulled valve cover and checked valves, they are all within spec. Pulled the carb apart and noticed a pit of play between the slid plate and the carb. Is this normal? Also is the seal on the slid plate a vacuum seal? or does it block all air from passing the seal?

  • kjadair91

Posted March 07, 2016 - 06:05 PM


ended up cleaning the carb las tnight pretty well (i think) and put it back on. it was too late to fire it up. so this morning started the bike and it ran fine no more hanging idle and seems to start when the bike warms up with the hot start. i read somewhere online that you can seal the slide plate seal so i tried that it it seems to work so far. but we will see when i take it out this weekend. only problem now is bog off of idle when i gas it quick. but i can deal with that over a hanging idle and no start when hot. im running a 168 main not a 170. just found that out last night. 

Edited by kjadair91, March 07, 2016 - 06:06 PM.

  • NW Briff

Posted March 07, 2016 - 06:26 PM


As long as your jet and needle settings are correct and accelerator pump works properly it Sounds like you still have blockage somewhere or vacuum leak. Did you remove the a/f screw and blow the passageway with compressed air? As well as the jets? Inspect/replace the a/f screw oring as others suggested?

Also check your fuel lines. I have seen them degrade due to ethanol. You clean the carb, fire the bike up and proceed to suck a bunch of black crap in it and your back where you started.

Edited by NW Briff, March 07, 2016 - 06:44 PM.

  • kjadair91

Posted March 08, 2016 - 03:30 AM


I did not replace the a/f screw o ring. Local dealers are closed on Mondays. But I put a new fuel line on when I put the carb back on. I also sprayed carb cleaner all around the carb, boot and air cleaner and did not notice a bog or increase in rpms.

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