KLR 650 2010 pilot jet

[David JonesMember]

I have replaced the standard needle with a KLX needle that i bought from Schnitz racing,and using the recommended settings of #140 main,#2nd clip from top,1 3/4turns out mixture screw,removed the airbox snorkel and using a Staintune muffler.Now the bike goes great but when on a closed throttle and slowing down in gear,it pops and bangs, but not above 3000 rpm ,only from 3000 and under.So i am thinking it is a bit lean on the pilot jet.The bike shop (Canberra Motorcycle Centre) says no other pilot jets listed/available .When i put the muffler on i removed the header pipe and scotch brite and brake cleaned,then used threebond 1215 (grey) where the pipe joins the head,and where the muffler slips on too,tightened it all up and let it sit for 24 hrs,so hope that its not sucking in air and thats causing it to pop and fart.I don’t remember the stock muffler making the pops and farts as it was so quiet.So if you have a KLR and it pops and farts too for any reason and or you have cured it or know something that might work please let me know.Like drilling out the stock jet or just using ear plugs. Thanks Dave

[Nathan HeatherMember]

Try closing or opening your air screw half a turn it should be used as a fine tuner sort of. Does it bog when you crack it open? There will be more pilots available then what they tell you, What brand carb? Welcome to the site.

[Adam RodgersMember]

Dave,

The pilot jet works together with your mixture screw. If you have set the mixture screw whilst idling correctly i.e. idles nice and smoothly (screw idle screw in and or out to find the best idle having set the idle to correct revs) and your in the recommended range for turns on the mixture screw (check you manual or web) then at least you know you have the correct pilot jet. If your more turns on the mixture screw than recommended then you need a larger sized pilot jet and visa versa for too many turns in.

If all is good double check for air leaking in the manifold.

Hope this helps.

Adam.

[Nathan HeatherMember]

I also found this little piece.

Deceleration Pooping/Hanging Idle
Popping: I frequently hear someone say “I have popping in the exhaust under deceleration so my carb must be lean!” Deceleration popping tells us a couple things;
1: Inside the exhaust pipe is hot.
2: Idle circuit is allowing fuel into the engine.
3: Somewhere the fuel in the exhaust pipe (which is not burnt as we are not allowing oxygen into the engine) is coming into a source of oxygen! Thus finding some air so it can explode!
That’s it! It does not mean its lean! You can richen up the idle mixture until the exhaust is no longer hot and the popping may go away? But now you have a cooler combustion chamber and the AC pump is going to have more trouble getting the engine to respond to the twist, you may find yourself going around in circles?
If you want to understand the engines function better? The engine is a big air pump, as long as the engine is turning over it is trying to draw air in. That airflow is blocked by the throttle slide so under deceleration there is very high vacuum on the front side of the slide.
What is happening is a combo of two things:
1: High vacuum at the intake port is sucking fuel from the idle circuit, that tiny orifice forward of the slide so some fresh fuel is being run thru the engine, as the air supply is almost closed off this fuel goes thru the engine mostly unburned. (BTW, several years ago when cars got FI and the mileage improved! The reason the mileage improved is the FI shuts off the fuel when the vehicle is driving the engine).
2: Under deceleration high vacuum as the exhaust valve opens before BDC at the end of the power stroke it draws air from the exhaust back into the engine. The exhaust had momentum going out, suddenly there is suction making it reverse. At that moment the suction at the exhaust valve area is so high that the tinniest leak at the head pipe will draw in fresh, dirty air!
“Fresh” in that it has lots of Oxygen! This ignites the un-burnt fuel out in the exhaust port!
Dirty in that it brings with it dirt that is around the front of the cylinder head, this gets under the valves and causes some minor pitting of the valve. Not catastrophic but when I take a head apart I have a pretty good idea of how good your head pipe seal is! (it has been a growing problem since the Siamesed pipe design that KTM went to in 04).
Dave’s way;
1: Do not use popping as a gauge to lead you to modifying your jets,
2: Remove the pipe, seal its inside with high temp silicone, let it dry a few days before you start the engine.

[David JonesMember]

Thanks Nato.do you think i should take the bike for a run on a dyno and that way they can put a sniffer in the exhaust and that may give an indication of whats going on? .Also will let me know how much power its got too. Thanks again for your help/info i am a Cabinetmaker and not a Technician,thats how i came up with the drill idea…

[Nathan HeatherMember]

I dont think I would bother with the dyno but others might. Try the air screw first.

[David JonesMember]

Thanks Adam i shall turn in the pilot /mixture screw half a turn and see/hear what happens.I thought i might blag a ride on the demo bike at the dealer and see what it does.

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