All 2st Thottle opening by itself

I was riding yesterday and the bike died like it had the kill switch put on and then it went to full wide throttle opening by itself .
After restarting it was ok again . Did this about 10 times on a 3 hour ride . Fun!!
38 PWK carb . Slide was still working fine and wasnt being pulled on by the handlebars or anything like that.

I ve just read this can be caused by the vents getting blocked
and sucking the slide up .
Would that be it ? It was definately coming on buy itself to full throttle after going over a bump or something .
If thats the case its one to watch out for as ity was not fun
and I couldnt work it out on the trail

This could be an air leak.?.? Had this happen with my old 2 stroke and it was an air leak and a dirty carb jet.
What do you guys think? Air Leak?

Could it be the vents pipes getting pinched ? sucking the slide up.
the slide is moving up by itself.... Could it be the mikuni gremlin in there playing with the keihin
I cant see bike right now to check vents - but it works fine then does it again

On rare cases I have seen where the needle may not be in right.
Maybe the pilot jet blocking too as you are reporting the bog and then full thottle.

Keep us posted

Chow, Carl

vents: clogg or pinch? bike dies/bogs.

slide is hanging open. wont usually go wfo unless the slide is open. if needle is bent/cocking, slide may not go back down/hang up. check for spots on the slide where it looks like it's scuffing. check for kinked spring. pull entire system: tube, cable, carb top, slide etc and inspect very closely. make sure needle aint cocking/installed werid. look for grit getting in and causing scuffing. something aint letting slide come back down all the way, if it truly goes wfo and wont shut. might even be a combo of things. if its super cold out slide can gum up. safety wire cable/boot thingy on top of carb/tube end so it cant pop out of noodle. make sure teflon insert in cable/noodle aint sneaking out- if so equipped.

not a good thing. get her issue addressed before yer next outing. lemme know what ya find. interesting combo of symptoms mate. not saying it cant happen but ive never heard/had it happen to me personally with a clogged vent. spring will close the slide everytime if things are as they should be, at least in my experience. it's prolly something simple but...get it sussed asap.

I did check needle and it wasnt loose or anything but will remove fully .

Before the ride I did change the clip that was holding the needle to a different clip ( one from the minkuni) As old one was bent . Maybe it is not straight . But that would nt expain it coming up again -
it does bog then goes ballistic .
I was trying to run the bike in and wasnt too good as a run in ride!! had to ride like a granny and wait for the fun to start .
Its probably self inflicted caused by amature fiddling too much

Mikuni and Keihins take different clips. The mikuni clip is thicker and will not seat properly in the keihin needle. I don't know if this had anything to do with your problem but something you should probably correct.

We had something like this happen this year with a PWK. Throttle stuck open several times, once of a jump face that ended up in an injury. We pulled the slide 3 times to see why it might be sticking and on that 3rd time I saw a tiny score on it. Checked the gas and bowl and found a tiny amount of very fine grit. Cleaned out the tank and carb and put in a fuel filter. Problem never returned. Those PWK slides have very close tolerance. Closer than the TMX. Check it out, it might be what's happening to you.

I think you were all correct . Vent pipes seemd ok and couldnt see anything obvious
I pulled out the carb and checked slide action
Appears that the needle isnt centred and on slight angle
Pulled out slide - there are scratch quite a few marks on the side
Took off needle clip - was seated ok but is thicker and slightly larger diameter
Put on the old bent up clip .
Noted that bolt that goes on over needle has a uneven shaped hole at needle end - not circular . Looks like its normal but could be worn?
With bolt down the needle seems to now have some play and movement - normal?
Back in the carby it sldes up and down and seems to be better centred
Hopefully that was the issue.
I still can t understand the bog and then the raising of the revs by itself

On a side note I dont really like the needle movement and when the bikes revving hard there is a slight bouncing sound at times which could be this looseness , Never had this vibrating noise with the Mikuni .

Thanks guys

It might be a good idea to check the reeds while you're in that area. Maybe a cracked edge not seating all the time.

If the throttle was not stuck in the open position then it would more than likely be running itself out of fuel. just remove carb, clean jets, be sure there is no blockage in your fuel line and or petcock. This will surely eliminate fuel as an issue. If the reeds were worn, you would suffer from hard starting and poor idle. Plugged vent lines usually cause the bike to run rich. However what I do to eliminate this possibility is trim the vent lines about an inch below the carb and slice the tube with a razor vertically.
If this does not help you message me and we can trouble shoot more from there.

I don't think the reeds are causing WFO throttle, I was thinking about the rattle sound or bouncing sound maybe a piece of debris bumping around and occasionally getting under the slide.

Thanks every one - I need to get an impact driver to remove float bowl screws - screws are soft. To have a look inside the bowl to see if anything is in there .
I will also get a filter on the fuel line but I dont think this is dit its not erratic runnning
I think jets are ok as it runs well until this issue comes on . Starts fine runs crisp but then the issue comes on when you think its all good.

The first time it happened I thought the bike had siezed - it just died very suddenly.
The next time it died for a second then went up to 9 to 10,000 .
The throttle slide was probably getting stuck due to needle angle but I dont know why it bogged first or came up . Even if the slide was going down to closed it wouldnt bog as it would still idle
I dont know enough about how carbs work to understand possible cause
Other noise -
I will look at reeds but I dont think it was happening with Mikuni -
The bounce noise seems to be coming from the carby . Would a float make this noise?
Sounds plasticy and like a fast vibration . I have notice this from first time i used Keihin but have been using it for 4 months and hasnt caused other issue
Thanks for the help .

replace them with stainless steel allen head screws. the stockers will go to crap on you if your in and out of the car enough

In the bowl there was a fair amount of sand grit but also two large
bits of crap - nearly 4mm in length!!
I dont know which way it came in
need to get that fuel filter
View attachment 7390

Bloody hell...they a boulders not particles

Where were they lodged or was it just freely sitting in the bowl? I would be surprised if you weren't leaking fuel as that would/should have wedged itself in the needle and seat which could have caused damage to your throttle needle.

I'd get in the habit of stripping the keihin regularly and blowing it down...cheap insurance

This is a handy vid:
http://www.videosurf.com/video/reas...retor-116625834?vlt=ffext&vlt_position=inline

They were on the top around the float , there was a lot of similar bits in the bowl when I flushed it
I think it must have come in from the tank
I always clean and oil my air filter but there does seem to some dirt getting in that way as well
I hate the air box on these things its always so dirty
I will keep checking more regularly

If you have dirt and junk coming past your air cleaner its not going to end up in your float bowl,its going to get stuck in your slide.If all that was in your float bowl then it came from your tank or vent lines.

I agree with Bill502...it would be a pretty good chance that those won't get stuck to slide but straight through to the reed change and then into the motor.

Fuel filter and again, regular checks with all the vent hoses and the carb in general.