hi all, i'm having a stressful issue with my trials bike. the idling rpm is wildly inconsistent, sometimes will lower down to a total stall, sometimes will keep raising rpm on its own.

nothing i have tried changes anything. when it does idle to where it sounds somewhere decent i will go to apply throttle, sometimes bogs, sometimes doesn't. on the occasions it doesn't it will rev up and stay at hight revs for a good couple minutes even when i only gave it the one blip of the throttle, it will very slowly and gradually make its way back down to idle.

i've had the carb off and cleaned a million times over, tried vacuum leak testing (none from what i could tell) and its had a new spark plug recently.

if anyone has any ideas it would be greatly appreciated as i don't want to kill the engine from it running like this. thanks in advance

2 hours ago, scotta said:

hi all, i'm having a stressful issue with my trials bike. the idling rpm is wildly inconsistent, sometimes will lower down to a total stall, sometimes will keep raising rpm on its own.

nothing i have tried changes anything. when it does idle to where it sounds somewhere decent i will go to apply throttle, sometimes bogs, sometimes doesn't. on the occasions it doesn't it will rev up and stay at hight revs for a good couple minutes even when i only gave it the one blip of the throttle, it will very slowly and gradually make its way back down to idle.

i've had the carb off and cleaned a million times over, tried vacuum leak testing (none from what i could tell) and its had a new spark plug recently.

if anyone has any ideas it would be greatly appreciated as i don't want to kill the engine from it running like this. thanks in advance

@scottatake off fuel tap and take it apart and clean it, then  flush out fuel tank , take off supply fuel pipe/tubing from tank to carb and blow it through  if it has a in line filter make sure it flows well or fit a new one. make sure breather tubing on top body of carb is clear into upper chamber of float bowl. check float height is 19mm if your carb is Keihin PWK28 and make sure your float arms are not fouling on your brass in overflow pipe in the float bowl stopping it from moving downwards fully also make sure the needle valve that lets fuel into the float bowl is not sticking in its bore  also make sure  there is nothing in the inlet rubber that leads to the cage that holds the reed valve petals , best to take it off and make sure the petals are secure and closing properly and they are complete.  Sounds to me like you have a slow / restricted supply of fuel  to the float bowl causing a change in air/fuel ratio but it could be something other of course. 

Air leak after the carburetor could do it, starved for fuel at the emulsion tube inside the float bowl part of the carburetor, faulty bottom end seal. 

Probably the death  barble. You need a set of security torx to take the jet tower off. The original oring shrinks. Best to order a replacement oring from Oko carbs as they are slightly thicker.

https://www.advrider.com/f/threads/keihin-death-barble.1285977/

@scotta If you decide to change the part that lineaway is referring to it is called a  jet block gasket. It sounds like it is a likely cause of your problems E10,  E5 fuel is not helping gaskets I would think , Its best to use fuel with only 5% ethanol at most , even Shell v power 99 ron has about 5% so thats no help 

A friend riding a 2023 gas gas 300 experienced the exact symptoms today, it was like omg and then he could hardly make it back to the house, pulled the carburetor and the low speed jet was completely plugged.  We ran a thin wire through the hole and that totally fixed it.

hi all, thanks for the responses

@Tr1AL tried this, the fuel tap was fairly clean inside and i've replaced the filter. sadly no change. 

@lemur sadly my low speed jet was pretty clear, give it a good go through with a wire and carb cleaner anyway but as with the previous suggestion. 

@lineaway got a full rebuild kit on the way from oko but am away next week so will have to wait until the weekend :(.

i dont even know what else this could point to if the carb and fuel lines are clear. anything to do with the engine itself possibly?

1 hour ago, scotta said:

hi all, thanks for the responses

@Tr1AL tried this, the fuel tap was fairly clean inside and i've replaced the filter. sadly no change. 

@lemur sadly my low speed jet was pretty clear, give it a good go through with a wire and carb cleaner anyway but as with the previous suggestion. 

@lineaway got a full rebuild kit on the way from oko but am away next week so will have to wait until the weekend :(.

i dont even know what else this could point to if the carb and fuel lines are clear. anything to do with the engine itself possibly?

It is more than likely carb related if it was running OK at some point and has since started running badly then it must have a blockage somewhere in a passageway  that can be rectified by cleaning everything in a ultrasonic bath or hopefully fitting a new jet block gasket will cure it. Best of luck.