Kx250f No idle,lots of backfire.

[Krossipoiss]

Are 04 original valves titanium or steel ?

 

[Ol'89r]

Are 04 original valves titanium or steel ?

Steel exhaust, Ti intakes.

 

[Krossipoiss]

New valves and springs (kibbles) and dynojet stage1 installed now.
With choke on bike runs great, but when choke is off, it starts to backfire and when hitting kill switch a small flame gomes out of exhaust...
What could be problem ?

 

[whenfoxforks-ruled]

What is a dynojet stage 1? I sure hope its not generic jets.

 

[Matt90GT]

hot start is stuck open

 

[Krossipoiss]

Cable is fine and when i release hot start handle, it pulls itself back nice..

 

[whenfoxforks-ruled]

Is the fuel screw effective? Where is it at, how many turns out? What size pilot and leak jet?

 

[Krossipoiss]

Yes it is. 1.5turns out.
Now theres new problems:
Backfire while decelerateing.And after ca 10 minutes riding bike will die and after stopped it goes from first kick. Jetting or ignition problem ?

 

[helio lucas]

seems that the carb isn´t getting enough fuel on sustained fast riding or ignition goes with heat.
check fuel lines, tap and cap. let fuel drain to a deposit or tank and see if flow breaks down with time, or enough fuel is flowing.
the ignition specs are very simple and quick to check, per service manual. all you need is the blessed book and a multimeter (or electrical tester).

simple and faster procedure first?!?!?!?

 

[Krossipoiss]

Have checked all fuel system, cleaned carb for like 10 times.
Could it be caused by bad fuel ? I'm runnin on last autumn 98(euro.)
Couldn't find how to inspect ignition....

 

[helio lucas]

i am in europe as well (portugal) and haven´t any problem with fuel unless it´s really old. it doesn´t hurt to buy a litre or something to be sure.

ignition is tested buy measuring resistance (ohm) and voltage (volt) of the stator coils, high tension coil and cdi.
you really must have the service manual for this one.

if you don´t have one, shoot me a pm. eventually i may help you.

 

[whenfoxforks-ruled]

Sounds as if the pilot is correct. What size is the leak jet?

 

[Krossipoiss]

Had some time in garage...
Main jet is 150(dynojet, with new adapter and needle) Without dynojet bike didn't even run.
Pilot is 40
Leak is 60
And the last one(starter jet???) is 56
And i also discovered that blue wire was loose from throttle sensor..

Cleaned carb and put on new spark plug. With choke on,bike runs nice. Without choke= fast/high idle, backfire.

 

[whenfoxforks-ruled]

You did not type the mixture screw position? You may need 2 sizes bigger pilot jet.

 

[Krossipoiss]

Mixture screw is : http://images.motorcycle-superstore.com/ProductImages/OG/2007_Sunline_Fuel_Mixture_Screw_Red.jpg
and only 3/4 turns out.
So i should try 42 pilot jet ?

 

[Krossipoiss]

Brought 42 and 45 pilot. Tried them both, nothing changed.

 

[whenfoxforks-ruled]

What about the ap circuit?

 

[Krossipoiss]

What is ap circuit ?

 

[whenfoxforks-ruled]

Accelerator pump. And where is the mixture screw at? I do believe you went the wrong way with the pilot jet size? You should have tried a 38 or something.

 

[Krossipoiss]

Popping/Backfiring = pilot jet too lean
Hard starting = pilot jet too lean
Unable to idle = pilot jet too lean

Too lean= too small pilot jet ?!

When i pull trottle, ap sprays..
Mixture screw is 1 1/2 turns out.

Bike ran ok with choke on(mixture was richer?) and backfire when choke off while idle and deaccelerate..

 

[whenfoxforks-ruled]

The top 3, you can write rich and have the same issue. The ap is timed correctly, the mixture screw says the pilot is correct, so the choke says put a bigger jet in. That leaves the leak jet. Put a bigger leak jet in, its actually has smaller number. Triple checked the timing is spot on? Do you know the throttle position sensor works? There was once, after a very nice valve job, some still leaked a tad? 1 other time, the very small o-ring atop the mixture screw and washer had issues, popped and ran with issues?

 

[Krossipoiss]

Leak jet is 60 atm. What should i try ?
Timing is right. Not sure about the throttle position sensor..
Will check valves for leaks. Washer and o-ring are new.

 

[whenfoxforks-ruled]

The mixture circuit, we lost that real small o-ring, later found out it got shoved up, and broke up, into the passage, it was a real bugger to dislodge and remove all the parts. And popped until it was clear. Look on a parts micro fiche, and order a leak jet with a lower number. I have only seen Honda in 06 and older that was off, for the record. This was also confirmed with JD jetting by the way. And Yamaha power jets are supposedly the same sized jet.

 

[Krossipoiss]

So, i'll try 50 and 55 leak jet..

 

[whenfoxforks-ruled]

Yes, and those numbers sound more familiar than the 60! Especially the 55.