jetting advice again

[Cox76y]

Hoping one of the jetting gurus on the forum can suggest a fix for me.. Currently I am running the stock n7 slide,Necj#2 mj172 pj40 air screw about 1 n half turns. The problem i am having is coming down off the throttle to the idle\pilot jet I have a bit of engine noise that sounds very similar if not the same as pipe banging. I know that generally pipe banging is associated with running rich but I have already gone down 1 size on the main.
Is anyone running a 170 main on there 2018 300 or is there a chance its actually running lean on the pilot and making a sound very similar to that pipe banging noise?? Plug looks ok, there is spooge coming out the exhaust but this could be from running the bigger main jet previously.
thanks
Josh

 

[taylor146]

hi
had similar issues with my 2018 300, was using NEDH 3rd clip with 42p and 175 main after the reprogram. I'm in the uk using 98ron fuel and through the heat of the summer seemed fine. last time I raced the bike in cooler conditions the bike was knocking /banging with racing idle when I CLOSED the throttle after a lot of 3/4 - full throttle fast riding, if your trail riding does not seem to be a problem. did some testing and by raising the main to 178 and richening the idle screw managed to reduce the problem, maybe excessive combustion chamber / exhaust temps igniting unburnt fuel. measured the squish and its 2.10 mm at the edge of the bore so too big, I'm thinking this is maybe part of the problem. Piston shows no sign of over heating, seriously thinking of getting the bike on a dyno.

 

[Gasser Nate]

I had almost exactly the same issues, mine were a loose rotor bolt that the loctite had set on before it was up tight against the rotor and excessive compression fixed with a machining of the head.