There are 4 circuits in the carb, any of which can be independantly rich or lean. Focus on the idle circuit for the backfire on throttle letoff. You can have a situation where the main is too rich, but still be too lean on the idle circuit.
If you get to the point where the mixture screw is 4 turns out, then youll need a bigger pilot jet.
A good way to confirm for yourself, that its too lean on the throttle letoff, is to pull the choke on, right before letting off the throttle...it wont backfire, or pop. And it isnt really a choke..it wont restrict any air, the choke lever opens up a starter jet, which just enrichens the mixtures.

 

thanks hondabuster for the info.. i will have to try that and see what happens. i will test that on the weekend hopefully and get back to yas.

 

Buy a stage 1 dyno jet kit a out of denniskirk and set it up just the way it says, I did but I went with the bigger jet it says you can if you run a pipe or what ever... Mine runs great

 

i tried mine at the settings that came with the stage 1 kit. it didn't work very good. which jet did you use? what setting for the neddle and what about the air mixture screw?

 

i know the post is old but did you ever fixed your problem?

 

I had the same problem with all 3 of my yamaha's and then a buddie pointed out that they require at least 90 octane (there should be a sticker on your air box) so now i only fill up with preminum gas and all my back firing and hesatiton has stopped