125-200cc Mystery problem on new bike

I have a new 09 WR125 with the factory 144 kit installed by the dealer. I also put a new PWK on it before I rode it. Last weekend I put 18 miles on it and got the jetting about perfect and had to make a power valve adjustment. This weekend I took it out and it ran great in the morning. It was a very hot day so I leaned the needle a clip later and rode for about another hour and a half. Then the problem started.

I would crack the throttle and it felt like I was running out of gas. If I would just hold the throttle position after a few seconds the bike would pick up and feel like it was running fine. I rode back to my truck to investigate. I checked the fuel level, the vent cap, I removed the fuel line to check the flow, and I pulled the plug. The plug was chocolate brown so I don’t think I had a dangerous lean condition but can’t be sure. I started the bike and it ran fine for about a minute. Then I climbed a big hill for another minute and the problem started again shortly after. I think the heat is having something to do with it. I did not have time to work on it last night but here is what I plan to do.

Electrical – the stock plug cap is a known problem which is why I bought a NGK one already, just haven’t put it on yet. I will install it then check the ground points and put some dielectric grease on all the connectors while I check them.

Fuel – I will pull the carb and look really close for any signs of dust. Then I will check for a blocked or loose jet and clean it really well.

Air leak – I already put some gasket forming stuff on the V-Force when it was new but maybe I should get an actual gasket? I also need to check the torque of the cylinder and head bolts. I should make sure my shock spring is not sawing through the air boot at the same time.

I am not sure what else I should check? I hate problems like this because if I do not find an obvious cause I have to check everything. If anyone has any idea what the likely culprit is please let me know.

Thanks

Maybe the float is sticking? Bad fuel?

new bike?
Believe it or not.....check in tank filter. Crap could have gotten in at some time. Anything from plastic bits to other debris. Just cause it is new to you....does not mean it was isolated before it got to you. Rare but known to happen.
Joe

I don't think there is a fuel flow issue, at least it looks good. When the bike was new I removed the tank and dumped all the fuel hoping to get any plastic junk. The bike has had a fuel filter since new. The fuel was the same all day so I don't think it is bad.

The float bowl sounds like a good thing to check.

Was there a specific RPM range it would bog or was it anytime you cracked the throttle? Something with the power valve? Sticking? Spring broke?

Once it got past the "running out of gas" feeling, which would last a few secnds, it felt good. I did not test it past the midrange though as I was not sure if I had an air leak or some other lean condition. I will pull the power valve cover and make sure it all looks the same as it did when I last adjusted it. Unless I see an obvious problem it sounds like I am going to have everything apart! Oh well, it is too hot to ride anyway. Thanks.

Love to know what is the issue was you have it sorted.

Hasnt there been a few posts about floats sticking on keihin carbs?
Try the Mikuni again - that will tell you if its the carb
I bet my left nut it is

Before you go to crazy, put the needle back to where it was when it was running good. I had been having basically the same problem with the mikuni and pwk, and the cure is more fuel.
GP

Update- I just spent a couple hours in the garage. The only obvious problem I found is that the cylinder base bolts were loose. A couple were probably only about 10 pounds. I knew I should have checked them before and after the first ride. Maybe they would leak a little air when I first hit the throttle and then once some vacume built they sealed up? I torqued them to 14 which I think is correct.

Before this I pulled the carb and the float worked fine and there were no plugged jets. Also there was no sign of dust.

I pulled the reeds. Looked good.

I pulled the power valve cover and the spring was fine and it was in the correct adjustment.

I pulled the tank petcok apart and out of the tank and there was no debris in it.

I looked at all the electrical connections and they seem good. I still need to pull them and apply dielectric grease and also make sure there is no paint on the ground points. I'll put a NGK plug cap on also.

I guess I will give the bike another try and if the problem returns it is off to the dealer.

Was it having issues before you adjusted the PV on the first ride? Did you change jetting to see if there is any change?

It was a little flat on the bottom before I adjusted the power valve. I did lean the needle a clip that day but it was over an hour earlier. I was pulling big hills with no problem and it only got hotter from that time so I am sure it was not the jetting. It did not feel exactly like a lean bog anyway, more like running out of gas. I am thinking that with the loose cylinder it could not make enough vacume to pull the reeds open and suck in fuel. At least I hope that is the problem and it is solved.