New miss in bike

My son's 04 crf450 developed a miss this weekend at the track and I'm trying to figure out the most likely causes before this weekend.Bike ran fine at practice on Saturday. At end of the day i added some Lucas ethanol treatment to the gas but did not run it through the carb. The next morning it started very quick but shut right off, did this several times, then i drained the carb bowl. bike missed first half of moto and then did better. Then i adjusted the fuel screw out ? (clockwise 1/4 turn) ran good the second moto. Today he rode again and said it was acting up when he turned (always to the left.)

It has a new plug, valves still in spec, compression 70, spark looks good. Any suggestions what to check? After reading what i wrote about the left turns i'll probably check to make sure the throttle cables are not binding some way. Any suggestions would be appreciated. Thanks Ed

So you put a fuel treatment in and then started running shitty?

How about trying this, drain the gas, add new gas WITHOUT THE LUCAS, then try it. You don't need the Lucas anyways. Hey seanc, you should be a cop, good investigative skills.

I appreciate the replies and I would have thought ethanol treatment too if it had missed in the second moto, but it ran fine. I didn't put different gas in it for the second moto. I also would not expect the fuel treatment to bother it only in the turns. I'll try untreated gas but honestly will be surprised if that completely solves the problem. Thanks Ed

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