i bought a 36 mm flatslide mikuni with accelerator pump for my 426 ex.Im just
wondering if anyone can help me with jetting sizes.My bike has 11:1 comp,head has
been ported ,web 150/151 grind cam,wb full
system,k&n filter with open air box. The standard
carb had 165 main jet,42 pilot and 1 notch down
on the needle.Should the jet sizes in the mikuni
be the same as the standard carb(the mikuni has flat jets)Any help would be appreciated.
oz_400ex

 

I could be wrong, but I believe Mikuni makes just two types of main jets; a hex head and a large round, slotted head and the size selections are equal, tho possibly not as wide a selection in both. Not sure what you mean by "flat jets", and if I understand you correctly you have the jet needle raised to the 4th position. As a suggestion, if you are just starting to re-jet, I'd return the needle to the 3rd, or nominal position, in order to focus on jetting your main first. (one adjustment at a time,mate). After getting the jetting for the top end of the band, then focus on other problems, if any, in the other parts of the band. I assume you are at sea level, i.e. 1200' or less elev. so I'd start with a main jet two sizes fatter than stock & do a test/plug read for the 3/4 to full throttle section of the band & go from there depending on plug color.