motor always runs cold 58cc Grubee Starfire

I am running a 58cc Grubee starfire motor on one of my bicycles.It's hard to start also after a 30 minute ride if I leave the bike for 15 minutes and re start it it is like starting it from dead cold.I haven't had this problem with my other motors.With them once I have started them at the beginning of the day they are easy to re start all day.
But with this 58cc Grubee it's like trying to start a motor on a cold day even if the motor is warmed up on a hot day.

Any thoughts?

adam valentine said:

yep I have the same problem a new cdi will fix it it heats up expands enough to not make connection then it cools down makes enough contact to work try a cdi off of your other build and it will start when its warm

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Thanks mate.I'll give it a try.

I still have this problem.
So far I have:
Changed the CDI.
Changed the spark plug.
Changed the fuel mix from 18 to 1 to 25 to 1 and added a fuel booster additive.
Changed the carby.

I am reluctant to replace the magneto as the jackshaft kit makes it very hard to get to and a major job to replace the magneto.

Any suggestions?