Hi,

Posted in expert section, but have more info.
2005 kazuma 250, appears cn250 engine clone.

Quad bogs down on low end and when I start to accelerate and will jerk until I hit 5mph and then will be ok above 1/2 throttle. Runs better once warmed up. but will die when I slow to a stop.

Hard to keep it idling for 1st 10 minutes.

Cleaned carb, its spotless, replaced spark plug. adj carb mix screw does not seem to help.

Any help, I was thinking auto choke might be issue, whats normal voltage.
Poss valve adjustment needed.

It does have an aftermarket unifoam filter.
90 degree weather, 2000ft elevation.

Thanks,
Jason

 

Normally the bystarter valve (auto choke) fails in the "enrichen" mode such that the quad starts up fine and runs progressively worse as the engine warms up. That is backwards from what you describe. I suppose it is possible that the choke could stick in the heated, closed off, position - but that seems really unlikely.

Here is a link showing how to test the bystarter valve:

Troubleshooting

Click on the "electric choke" section...

The bystarter valve is powered (heated) by 12 volts (AC or DC doesn't matter since it is just a heater that heats and expands a wax pellet), but it is a little more complicated than that. Some quads power it off the raw AC output from the stator, but then put a resistor in series to knock the voltage back down to 12 volts at speed. Others power it off an auxillary output from the voltage regulator that is separate (diode isolated) from the battery charge output. This is so the bystarter valve is only heated when the engine starts up, and not simply off the battery voltage when the ignition is on with the engine stopped.

In any case it is powered off equivalent 12 volts (AC or DC), and is unlikely your problem.

 

It needs richer jets.. at the least a bigger pilot jet.. try turning the fuel screw out 2.5 -3 turns out from seated.. should help some..

 

OK, so I turned the fuel screw out like 5 turns, quad idles higher and better and also responded alot better, still dies when i come to a stop. Still had some jerking/bogging issues on acceloration.

Prior to that I duct taped over most of the air intake and also ran better. I am definately lean.

Can anyone point in to where I can get bigger pilot jets and size recommendations?
I also understand you can adj the main jet, any instruction on that would be awesome or new size for that also.

The kazuma is a cn250 honda water cooled clone engine.
I did also check for leaks at the carb.

Thanks,
Jason

 

I want to say Ive got a 45 or 47 pilot jet in my 250 and a 124 main jet.. ride at sea level to 3500 ft..

95% of the jets used in Chinese carbs are copies of Keihin jets.

Keihin jets are available at Honda dealers and ebay.

If you have or know some one with a number drill set..0-60 for the main and 60-80 for the pilot.. you can make your own.. but of course you can only make them bigger.. not smaller..

Jet sizes are in millimeters.

a 39 pilot jet is .39 X .03937(1mm)=.015 it has a .015 dia. hole..

a 115 main jet would be 1.15 X .03937 = .045 it has a .045 dia. hole..

 

The only "adjustment" for the main jet is the needle.. not a big difference but some.. the higher the clip is on the needle the lower the needle drops into the main jet(less gas gets thru) in a lower groove the needle is raised(more gas gets thru) It has no effect on 1/4 to wide open throttle.. that needs a larger main jet..

 

OK, so went to 45 pilot and 122 main and ran much better. It will still die when I come to a stop, but will idle once I restart and then once I slow to a stop again it will die. Played with fuel screw and could not improve.

Went to a 48 pilot but after reinstalling the carb, i noticed this hose was disonnected. See photo as disconnected at yellow arrow. It than ran worse. Unsure if due to 48 or reconnecting hose. Did not have to much time to mess with it.

http://i1097.photobucket.com/albums/...oser/pict2.jpg

Would that hose effect fuel/air?

Also where it T's up in the middle and connects at 2 spots, the middle T connects to a long hose that just hangs down, so it might be a slightly different cn250 version.

Thanks, as I seem soooooo close to be dialed in.
Jason

 

As long as that hose doesnt connect to the carb or intake manifold it shouldn't affect anything.. What does all that plumbing connect together?

What is the fuel screw set at? will the engine idle in neutral? how long? im wondering if the clutch is dragging when you come to a stop?

 

When I had the 45 pilot, it would start and idle fine, if I took a couple laps around the garage at 5 mph, it had slight hesitation, but close to perfect. When slowing down from 5 mpg it would typically stay idling. If I ran up to 20 mph and slowed to a stop, it will always die. I messed with the screw from 1-4 turns and still would not idle on slow down.

I put in the 48 and it was worse.

I figured I will put the 45 back in and play with the idle and fuel screw this weekend, as it seems close.

I will also test the auto choke. It has been 90-100 degrees everyday but I do not remember the quad idling any higher during initial start up.

Could valve timing be an issue. Ive seen buggynews where they adjusted the valves while it was idling, and just listening as the engine seems to have a slight clack. Just a little nervous.

‪250cc Valve Adjustment‬‏ - YouTube

Thanks for all the help!!!!!
jason

 

Was a solution on this ever found out? I have the same issue but with a Chinese Buggy, same motor. Idles fine, but step on the gas, it's very low power and barely moves the buggy.