250-500cc 09 WR 300 hot starting issue

[RobNewy]

Hi All,
My 300 is a dead set bitch to start when it is hot. Cold, not a drama, first or second kick
It goes like a cut snake, but stall it or stop for a breather, and it is a mongrel.
I'm assuming it's a jetting problem, but I'm not sure were to start.
#420 main
#40 Pilot
#80 Start Jet
Air Screw out 2 turns
Needle Clip middle 3rd from top
It was in the 2nd from the top, but was a bastard to start, hot or cold. I ride in temperatures from 10- 35 deg C and an altitude of 0 - 1000 feet.
Any help is appreciated

 

[Johnnymannen]

I guess you have tried to open the throttle while kicking it? Is it wet on the plug?

 

[BillO]

If it's hard to start hot, it might be a little rich in the idle circuit. It can be hard to get it perfect, but you could try a 35 pilot. You may have to richen the needle again if you do change the pilot, but probably not. Or just try cracking the throttle a little when you kick it hot.

You're not using the start circuit are you? I know it sounds like a silly question, but I have seen this done by someone used to modern 4T's. The guy though it worked like his old hot-start.

 

[krieg]

Try fiddling with the air screw in 1/2 turn increments. I'd start by going out to 2.5, see it helps... then go as far as 3. If going out on the airscrew helps put the next smaller pilot jet in it and start at 1.5 out on the screw. If that doesn't help, try the same thing going in with the air screw. If you have to go in beyond 1 turn out, then a try a bigger pilot.

Also, some folks have reported their reed valve gaskets leaking as the bike warms up. Wouldn't hurt to check that all is well with the reed valve and gaskets. Normally, however, when the reed valve gasket leaks air badly enough, the bike will run very lean and overheat.

 

[mkenn72]

On my 09 wr300 I am running:

460 main
32.5 pilot
Lowered the needle one notch (raised the clip)
Air screw at 1 1/2 out

Starts and runs great hot or cold. Basically all I did was lean the pilot circuit from stock. Bob at Central Jersey gave me a 450 main with the bike but we agreed it was running fine with the 460 so we kept it in. This is at sea level NJ.

 

[krieg]

On my 09 wr300 I am running:

460 main
32.5 pilot
Lowered the needle one notch (raised the clip)
Air screw at 1 1/2 out

Starts and runs great hot or cold. Basically all I did was lean the pilot circuit from stock. Bob at Central Jersey gave me a 450 main with the bike but we agreed it was running fine with the 460 so we kept it in. This is at sea level NJ.

Come to think of it, I think I was running a 32.5 pilot in my 2009 300 so the 40 is probably too rich.

 

[RobNewy]

Thanks for the input guys.
I will try the air screw first and see what happens.
I might invest in a few different pilot jets to.

 

[motosapiens]

I'm not the world's jetting expert, but I do own several 2strokes. I found a similar problem. I kept going leaner on the pilot, and cracking the throttle while kicking, but it persisted. I just don't think the mikuni carb works that well at idle or very small throttle openings. I screwed with it for as long as i had patience and then just shelled out $250 for a keihin carb from motosportz and called it good. I had that dialed in a couple rides. I think the air-stryker design works better at situations of minimal airflow (like starting).

I was riding in spring conditions here at the time, 3000-6000', 40-70 degrees, and went to a 32 pilot, then to a 30 (too lean) then back to a 32.5. With the stock needle in the top clip and a 450 main, that was as good as i could get, but the keihin starts better and runs better anyway.

 

[RobNewy]

The PWK is definantly on my list of things to do, but at the moment it's not an option.

 

[tony_dt]

If you are in the middle of a race or ride you might try this.

1. Make sure you are in neutral
2. Open throttle fully open.
3. Give a good full kick preferably just past (TDC)

This seems to work for me with my two stroke huskies. It seems to really work well with the Mikuni carbed ones.

Of course jetting could be your culprit as people have pointed out.

 

[Johnnymannen]

I'm not the world's jetting expert, but I do own several 2strokes. I found a similar problem. I kept going leaner on the pilot, and cracking the throttle while kicking, but it persisted. I just don't think the mikuni carb works that well at idle or very small throttle openings. I screwed with it for as long as i had patience and then just shelled out $250 for a keihin carb from motosportz and called it good. I had that dialed in a couple rides. I think the air-stryker design works better at situations of minimal airflow (like starting).

I was riding in spring conditions here at the time, 3000-6000', 40-70 degrees, and went to a 32 pilot, then to a 30 (too lean) then back to a 32.5. With the stock needle in the top clip and a 450 main, that was as good as i could get, but the keihin starts better and runs better anyway.

Totally agree! The Keihin is the best investment i´ve mad on my bike. We have about 10 degrees Celsius here now, sea level, and i use a 40 pilot, 460 main and JD red needle in 1st (leanest)clip or the EEL in second, airscrew about1 1/4 out, but it´s soon time for a 42 pilot as it´s getting colder. No spooge, nio plugs fouling, clean and crisp everywhere and starts at first or second kick hot or warm. If you decide stick with the Mikuni i can recommend a needle named 6DEY15-74. I used this in my Mikuni and it was much better then the 6 GAY69-74 that came in my bike with the "powerkit". Started easier too. You have to go down to sizes in pilot with this needle.

:sweden: Johnny