300 14 running great @ offroad and not @ mx

[BSM2]

Hi,

My bike is running great at offroad and enduro tracks.
Normally it has a very low, but strong idle and picks up quickly with a hole shot to the end, love it .

Only yesterday I ride at the MX track and was pushing the bike. Now the revs are hanging above idle and stay there. After 30sec it wil drop to normal idle.
My airscrew was 0,75turns out, and only when i turn it to close position, the idle was responding by dropping the revs, but now it wasn't idling anymore.

I'm running with the setup:
178main
45 leakjet
airscrew 0.75
Needle N3CJ #4
Altitude sea level and 15-20?C
mix oil 1:50

Normally I think to take a bigger leakjet, but i'm not a jetting expert and I see that everyone is running a smaller leakjat. So maybe I have to change the needle?
What do you gues recommend?

 

[bergerhag]

Perhaps float bowl fuel starvation, the flow of fuel to carb is too low. The air flow through fuel lid vent is sometimes too restrictive. Also check fuel line for debris.

 

[BSM2]

Perhaps float bowl fuel starvation, the flow of fuel to carb is too low. The air flow through fuel lid vent is sometimes too restrictive. Also check fuel line for debris.

Serious? Fuel flow to low? Didn't know that.
I will check that.
If someone else has some other good tips...

And i'm from origin not english minded, so can you please explain:
The air flow through fuel lid vent is sometimes too restrictive.

 

[wence]

The cap will create a vacuum in the tank if the breather is not working correctly. To check this undo the cap a little and then ride how you would when it bogs and see if it continues. If it does the cap is fine you would assume.
I have had a similar problem with the float level and the fuel tank debris.
I would definitely check the fuel tank and remove the pet cock and clean. I have put a fuel filter in line to stop the crap from entering the carb now.
Cheers Mark

 

[bergerhag]

The fuel cap needs to let air in to replace fuel that is beeing consumed. The flow of air is on some caps very low, and it almost creates a vacuum when bike has been running hard for longer periods.

 

[BSM2]

Thank you, I will check it

 

[desertgasser300]

your pilot seems rich for a 300?

 

[memphis2857]

Yes pilot should be 40 or 42 but with the hanging idle it sounds too lean. Check to make sure the carb is seated in the boot properly and that there is no air leaks anywhere


Sent from my iPhone using Tapatalk

 

[Jakobi]

Different fuels in different parts of the world. The whole setup is richer compared to what we would use in a 300 here, so I'll assume they have come to their setup through testing.

I'd check what others have. Blow out the pilot jet and check the float height. Check the cap is venting. You can do this by simply removing the cap from the bike and trying to blow air through from each side. It should only vent back into the tank direction and do so at a decent rate.

If that still doesn't work, I'd go one richer on the needle or main. Richer on the pilot will stop the hanging idle, but its likely that your lean running and heat is building up while sustained at open throttle (above 1/4 I'd imagine).

 

[BSM2]

Yes Jacobi, thank you.
I come to this settings through testing. The bikes runs the best with this setting, however didn;t ride a mx track until last weekend.

I have modified earlier the float height because it was leaking.
Perhaps I modified it to much, I will check this first! (and the fuel cap)