just had my 450s rebuilt and the exaust pipe at the motor end is getting cherry red does anyone no why rebuilt carb also

 

You are running too lean, that is why it is running hot.
You rebuilt the carb, did you use the same jet sizes?
Do you still have the same pipe on it after the rebuild?

 

yees put all back stock but thinking that the person that did the rebuild didn't set the valves just right oil ring was broke but nothing wrong with head

 

would that make it run that hot and changed the fan to but didnt come on till later, did come on though

 

you need to rejet it sounds like. idk where you located but its getting colder out and cool weather means more O2 in the air. that combined with the rebuild, im assuming it was bored a little larger, mean your engine is running leaner.

rejet to the next size main and adjust your pilot jet out 1/2 ish turn. both will richen you mixture and stop it from overheating

 

all this guy did was put new piston and ring in didn't bore it out any he wants me to run it for a wile and thinks it will get better because it has so much compression
i just don't know enough about it to say anything

 

how much compression? if its more than stock you do need to rejet and mabe try some premium gas in it.

 

Thanks, will try one or the other did put 92 octane in it with sea foam was not gettin as red but fan not kickin on eather oil not getting hot just the to end will tell him about the jetting thing buddy of mine set his at 4000 in and 6000 out some way and it fixed his