Okay so I bought a 450er as my first quad. It started right up at his house. Now all the sudden I am having a problem getting it started. I did the obvious tune up oil, filter, battery, plugs... But still after that it will not turn over it just keeps cranking.. Like I said I am new to this quad it might be something simple who knows..

When I bump start it it will start right up in second gear no problem.

Also sprayed some starting fluid in the air filter started up after giving it some gas..

After it is warmed up it starts no problem

 

Maybe clean the carb. Could be a plugged pilot jet.

 

It stays started once running tho...?

 

Honda gave the TRX450R a significant makeover for the ’06 model year. In ’06 it was mid to bottom of the pack compared to the Yamaha and Suzuki 450’s in stock trim. However, things changed once some modifications were performed and it leapt right to the front! Some changes made were to the headlight and cowl, engine, carburetor, ignition, airbox, exhaust, seat height, front end geometry, swingarm linkage, and an electric start version.
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Sounds like the valves need to be adjusted. It's a simple job but a common one for the trx.