Well I must say, this problem has been haunting me for quite some time.  When I start the quad I usuaully have to run it in choke to keep it running, even then it dies constantly.  The only thing I have found to get out of it is turning the gas to primer, but have to keep adjusting it back and forth to on.  After a while of doing that the motor warms up and gets a little better.  Now, to the big issue.  While riding, I get going between 20 to 40 mph, and it will backfire and die right their.
Usually I have to put gas in primer and choke it to get it going again.  I have had it looked at twice. Had carbuerator looked over.  They said they found nothing wrong.  I personally cleaned air filter and changed spark-plug.  I have ran alot of gas through it thinking I got bad gas.  I am stumped...any suggestions???  

yes check the diaphram in the top of the carburetor.
they may have overlooked a small hole in it.

if that's not the case then i would certainly take a look at the carb myself.

the carb may have been cleaned out but still got a little more trash in it from the tank once it was reinstalled.

also drain the tank see if there is water or trash in it.

also check the airbox and the airbox intake boot for water or trash.

it's possible that you have a worn valve stem seal, but normally those only worsen as you ride them more, and you would notice smoke from the exhaust due to oil burning.

also check the intake boot for cracks. ( the one in front of the carburetor.  

cool man thank you.  I will check it out.  Also, when I went to get part the other day, I asked for a new fuel filter.  They informed me that this model does not have one.  Is this common? It does not seem right not to have one.  

yes it really common.