White Brothers DR400T

[oldmxracer]

Well done! I like it....

[Curtis]

Hell yes! Love it. Strange that it pops when you wind out the mixture screw? Maybe try a slightly larger pilot jet, see what happens.

[FourstrokeForever]

I agree with Curtis. With you saying the header gets hot very quick that would indicate a lean mixture to me. Also, the fact that the problem (popping) gets worse when you wind out the mixture screw also indicates a lean mixture. Remember, the more air you put in by opening the venturi size, you will also need more fuel  I would enlarge both the pilot and main jets as a start.

[mick25]

Also check the header pipe is sealed good , take it off and look at the header pipe gasket and make sure the gasket is crushed all the way round so there's no air getting sucked in when backing off on the gas , if it's leaking it can make it pop to .

[Momus]

Check the ignition timing. It could be retarded if the pipe heats quickly.

[oldfart]

Come up one on the pilot   (Std  is # 15 )   

[pmc57]

From my understanding most 4 stroke carbs have their air (fuel screw) screw located  somewhere between the carb body and the cylinder. The further out it's turned the more fuel it allows hence making a richer low end fuel/air mix. This is opposed to a typical two stroke carb like a Mikuni where the airscrew is at the rear of the carb body and that by turning the screw out allows more air and a leaner mix.

Make sure you know which way to turn the air/fuel screw to make a richer or leaner mix.

Air screws at the back of carbs: turning the screw out = more air and a lean mix
Air/fuels at front of carbs: turning the screw out = more fuel and a rich mix