i run honda 20w-50 but i have that same problem with my 400 but it even did it with the stock exhaust
i know it burned the 10w-40 oil but mainly cause it had a little to much then it would stop
08 400ex , cut fenders, HMF slipon with modified stock header, 11:1 wiseco piston, stage 2 hot cams, burgard +2+1 a arms, rebuilt 450r shocks, tusk axle, rear itp baja rims with dunlop quadmax sports all around, racesin nerfbars and bumper, houser plus 1 stem with atv low bend pro taper bars asv lever streamline clutch cable and oury grips, rejeted 165 main jet 40 pilot and dynojet needle with K&N air filter, runs no airbox (sold)
05 trx 450r 13.5:1 je piston, port polish, stage 2 hotcam, full yoshi pipe, uni filter, +2 a arms +4 lonestar axle, stage 3 std travle elka, hiper rear rims, itp baja front rims, itp holeshots dunlop quadmax sport, bare gusset kit, quadtech hood, pro armor bumper, dg nerfs, +1 houser stem, protape atv low bend bars