Bike stalls when twisting the throttle

[blic]

(I post this here, cos I don´t seem to get any response on the thumper forum.)

Its a Honda XR650.
The bike stalls when twisting the throttle fast from idle to 3/4 or full throttle. Gear in neutral or in any gear.
No matter if the bike is warm or cold.
And I haven´t touch the engine before this started, it just happened.
After it has stall in this way I can´t start it up in first kick, that it usually takes. In second kick it will fire up.
The old sparkplug was black and sooty. I have inspected it before the problem started and then it was gold/brown as it should be.

What I have done:
Put in a new sparkplug.
Cleaned the carb. with air pressure.
Raised the needle jet one step, no difference so I put it back as it was before.
Tested without air filter in it (just for some seconds), to see if it was clogged.
Raised the idle, didn´t helped.
Played with air screw, didn´t helped.
Tried gas from another tank, nope...

So still the problem is there.

Jetting: 175 main, 65 pilot, needle in 3th(from up). Air screw 1 3/4 out.

Please help me out!

 

[cr25096er]

Sounds like the main jet is blocked or very lean. Has the weather changed lately? Did you remove each jet and look through it when you cleaned the carb? How well does the gas flow(from the petcock)? If i were you i would put it back to your original settings where it ran good. Do you think the float could have come out of adjustment? It has to be something simple...........

 

[whitesands26]

If you determine that your carb is clean and everything is flowing properly you may want to look towards the jetting...Does the bike sound like it's surging when you open the throttle or does is bog ? Surging would suggest a very lean condition and the bog indicates a rich condition....Based on your spark plug being wet and sooty it seems like it may be too rich.....

Also one thing you may want to consider is that the air temperatures are getting much warmer...Has this problem coincided with the warmer summer temperatures ? The warm air thins out the amount of oxygen for a given volume of air which will also result in a rich condition (less oxygen/more fuel).

 

[blic]

The carb is now 100% clean, cleaned it again. The gas flows good from the petcock. I have it in the original setting, haven´t changed it. And it ran good there one week ago, no weather changes.
When I use the choke in middle position the bike works better when I throttle it, but not good. Isn´t this a lean condition?
But the sparkplug is black, but not wet.

I´ve also been checking for leaks between the carb. and cylinder head. I´ve sprayed start gas to see if the engine start to rev when it´s running, but I can´t find any leak.

Maybe it´s the float, but can the float change by itself?
I´m also thinking of checking the valve adjustment.

I can also tell you that the idle is not steady, it goes up and down.

Thanks

 

[cr25096er]

try to richen the pilot jet.

 

[blic]

Isn´t jetting just a way to go around the problem, cos it worked a week ago in the same conditions with this jetting.

 

[falcon1]

Hey,
Maybe try checking the ignition system for faulty wires/connectors. I think your right that if you cleaned the carb thoroughly (blown the jets out well) thats not the problem. I think its in the ignition. Does it sound like the engine is missing/skipping at any RPM?