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What can I do to make an mx bike easier to start/make them run better

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My four stroke mx bikes are often hard to start and they just seem to run a little off. I don’t know why. I’m not really concerned about power, I just want them to be easier to start.

 

2005 Kx250f

2006 crf450r

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do they hold a valve adjustment?

the 06 crf was not a good year for valves/seats

do you have fresh vac release plate seals in the slide?

nice clean fresh pilot jets?

kick her through slow once and get the piston right after TDC, and use a long follow through kick to fire it up.

 

if they have ever sat for long periods of time they may need a full carburetor strip down, even mid body separation.

 

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Hard to say with bikes that are a dozen years old. The life expectancy of a motocross bike is measured in hours, not years. As William1 said, verifying that the engine is in good operating condition is step # 1.

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The engine is great, the hondas valves are perfect, the kx’s are a little loose. It’s about 20 degrees Fahrenheit where I am so that’s definitely playing a role, I just want them to be ready for the spring

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23 minutes ago, ryan_cin said:

The engine is great, the hondas valves are perfect, the kx’s are a little loose. It’s about 20 degrees Fahrenheit where I am so that’s definitely playing a role, I just want them to be ready for the spring

Hondas have always been cold blooded beasts.  Every Honda I've ever owned was harder to start when cold.  Street bikes and dirt bikes. 

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1 hour ago, ryan_cin said:

 

My four stroke mx bikes are often hard to start and they just seem to run a little off. I don’t know why. I’m not really concerned about power, I just want them to be easier to start.

 

2005 Kx250f

2006 crf450r

 

Jetting, proper valve adjustment.

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