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Kfx50 hard start / dies on idle

Old 12-25-2018, 08:13 PM
Weekend Warrior
Thread Starter
Join Date: Dec 2018
Posts: 4
Default Kfx50 hard start / dies on idle

I have a 2019 kfx 50 that takes a couple of tries to start (pushbutton) and dies on idle. The sound of idle sounds weak.

Sometimes when coming up on a stop after riding for a bit, it will die while idle. Runs fine otherwise.

If i open the throttle a little when using the electric starter, it starts immediately.

Should I adjust the idle by turning the screw clockwise to turn it up? Or do I add some carb cleaner to the fuel?

Supposedly the dealer checked everything before i left...
Old 12-26-2018, 05:02 AM
Extreme Pro Rider
Join Date: Oct 2013
Location: Lancaster England
Posts: 3,522

Adjust the throttle stop screw a bit. However new engines are a little "tight" and idle speed rises as an engine warms up anyway, so you may need to slow it down again once warm, or after the engine is "run in." It is quite common on non fuel injected engines, to need a little throttle when starting.
Old 12-26-2018, 01:06 PM
Weekend Warrior
Thread Starter
Join Date: Dec 2018
Posts: 4

I got a newbie question - how much do I adjust the idle speed screw? Is 1/8 turn too much? I bought a contact tachometer, but it won't arrive for a couple of days, so I can check if the idle is ~2,000RPM per the manual.

Sales guy said it wasn't run for a couple of weeks, so he drained the carb and switched to reserve to get it started. It wasn't exhibiting starting issues after that. Then they took it in the shop to get it tuned (I didn't test starting then) and this started happening when I got home.

Any answers are appreciated as the little guy is exciting about riding it.

Before adjusting idle speed

Without throttle, the KFX50 doesn't start most of the time. Sometimes it starts after lots of attempts, but the idle is "weak" and dies after 10-15 seconds. Video:

With light throttle, it starts immediately. When cold, releasing the throttle will cause it to die either immediately or after 10-15 seconds. When warmed up, it may still die when coming to a complete stop and letting it idle for a couple of seconds. Doesn't happen all the time. Video:

After adjusting 1/8 turn clockwise to increase idle

After adjusting the idle screw 1/8 turn clockwise to increase idle, it starts within 2 seconds of cranking. It stumbled the first time after a bit, but it was still cold. Video:
Old 12-27-2018, 04:25 AM
Extreme Pro Rider
Join Date: Oct 2013
Location: Lancaster England
Posts: 3,522

Yes, the last video shows the machine working fine, idle is still a bit slow, but will probably increase as the engine warms. As long as it doesn't rev high enough to set off on its own, and doesn't stall, the idle speed is OK. Like I wrote earlier, most bikes fitted with a carb need a bit of throttle when you are starting them.
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