Posts
6161
Joined
1/31/2018
Location
Mansfield, OH
US
Edited Date/Time
11/19/2019 12:40am
My kx250f is backfiring as the rpms fall. Head, valves, and cams are new & in spec. Motor has stage 1 hot cams. I run cam2 110oct gas. Carb was taken to a dealer to be cleaned. Running condition did not improve. Tried going from a 40 to 42 pilot jet & backing the fuel screw out & it still backfires. Sprayed carb cleaner around the boots and it made no difference. The bike is running lean obviously. Below is a video of what mine is doing(not my bike however). Mines also not quite this bad. Additionally theres a hanging idle. Forcing the throttle forwards seems to help that issue.
https://youtu.be/yb7wEYvHf4w
Not sure where to go with this. Sadly my local kawasaki dealership has zero clue where to go with this issue either.
https://youtu.be/yb7wEYvHf4w
Not sure where to go with this. Sadly my local kawasaki dealership has zero clue where to go with this issue either.
Also check for air leaks at the carb to head manifold.
Also remember that running too high an octane fuel can cause issues as the fuel burns too slow for the engine application. I can see no reason for the use of 110 octane, but here again I don't have all the engine spec's either.
Paw Paw
Wiseco Racers choice piston
Stage 1 hot cams
Prox SS valves & spring kits
Exhaust seal is new & the bolts are torqued to spec. Should i put anything like anti seize or copper silicone around the header where it goes into the head? The joint to the muffler seems ok, i cant feel any air coming out.
Also the dealership mechanic sprayed carb cleaner all over the air boot on both sides of the motor & it did not affect the idle. Im almost lead to believe the choke or hot start is leaking - i have a brand new pluger, seal, and oring for the hotstart.
As far as the gas, im assuming your logic is its not burning fully, thus being expelled into the pipe and burning off from the heat?
You may want to try and reduce the octane and see how that does.
Paw Paw
The Shop
Paw Paw
When i first got the bike, the hot start was seized in the hole. I pulled it out and replaced it. Is there a chance air is leaking through it even tho its new with a new spring & seal? If the plunger isnt seating fully with that allow air past the seal?
Paw Paw
https://youtu.be/nnp63CTYhJw
My recommendation
Replace hot start
Set float bowl height
Check proper jetting
Reset idle
Set accelerator pump timing
Paw Paw
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