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Technical Motorbike Help

KMX 125 won’t start

KMX 125 won’t start - Forums [Biker Match] KMX 125 won’t start - Forums [Biker Match]
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KMX 125 won’t start

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Any ideas? Cleaned carb, it’s sparking normal yellow/blue, compression fine, cleaned spark plug. Fuel tank full. Fuel getting through fine. Won’t bump start either. It’s supposed to be going to the TT at the end of the month. Any ideas would be greatly appreciated

   Update Reply
ElegantTomboyZenmaster @ 02/05/2023 17:31  

Check the Air filter. Change the plug even if its sparking it could be failing and only producing a weak spark under compression. How old is the fuel if it has gone stale it cause starting problems when cold as it loses its combustibility ?

   Update Reply
JP @ 02/05/2023 18:11  

Have you had the bike long ? Could be lack of compression. General engine wear and tear, worn pistin rings. If you have weak compression then that could be your issue.

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Deleted Member @ 03/05/2023 05:42  

Hiya you could remove the sparkplug and pour a tiny amount of petrol and 2 stroke mix down the plug hole n see if that will start it..used to do that with my motocrosser if it was refusing to start once running it would pull the fuel thru ..also check the petrol cap breather isn't block ..try starting it with the cap loosened ..

   Update Reply
Deleted Member @ 03/05/2023 07:16  

Do a leak down test if you can't get it running or take it to someone who knows two strokes.

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YammiBrett @ 03/05/2023 07:22  

Although you have cleaned the carb, the pilot jet could still be blocked.

With 2T's when they have been stood the fuel/oil mix turns to jelly and eventually into a hard lacquer, which can take some shifting.

To check if fuel is going into the chamber, take out the spark plug, use some kitchen roll on your finger and cover the hole, crank the engine a few times and if you have fuel the paper will be wet and will smell strongly of fuel.

The problem could also be too strong an oil mix, as suggested you could pour some fuel mix down the hole first, but make it a weak mix, so you have a good volatile fuel, be prepared for a big bang on the backfire when it catches.

If you still have problems, I don't mind coming down to help out.

   Update Reply
dynax @ 03/05/2023 07:43  

Sounds like
You’ve already covered the basics, if you’ve not tried using a squirt or two of easy start into the air box (removed the filter) obviously easy to do if you get someone to squirt the easy start in as you kick it over. If it fires / tried to fire. It mostly likely a carb / fueling issue. These old machines don’t like modern unleaded petrol and while you’ve cleaned the carb, the best way is a total strip down of the carb and get it ultrasonic cleaned so it gets all the minute drillings / coatings clean too. I’ve had your problem with several bikes and it was the inner parts of the carbs all gummed up. Failing that if you’ve put a new spark
Plug in just try using the old one. I’ve had brand new spark plugs breaking down under compression but actually spark fine when tested. Oh check all
The HT coil connections too. Good luck with it. Rich 😎

   Update Reply
richie203 @ 08/05/2023 10:38  

Did you get anywhere with the bike ? Fixed or still not running?.

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Deleted Member @ 08/05/2023 19:03  

go easy with the easy start , have known people ruin a engine with that stuff ? ,

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baxi @ 19/05/2023 10:14  

Did you get the KMX running, was it running before this time, if so was it parked up for long ???.
I dont get on here much, so may be a while to see your reply.

   Update Reply
BIKEABOB @ 10/07/2023 14:46  

turn the kill swich back on lol

   Update Reply
alegsx @ 30/07/2023 21:40  

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