#Mikuni pilot jet sizes how to#

Good jets can vary as much as 5% cheap jets can be closer to 10% variance. None of the above takes into consideration the changes in fuel vaporization characteristics as you change altitude, which can have a profound impact on the final air/fuel ratio available in the combustion chamber ( the only place a/f ratio is really significant anyway) when the sparkplug fires.ДЄs fun as it might be to look at jetting this way, the sad fact is the cross sectional area of two jets marked with the same number can vary FAR MORE than the difference in flow due to small changes in density. Weight of fuel = jet area * ( SQR Root (head pressure * fuel density) In simplest terms fuel weight is a function of the area of the jet multiplied by the value of the square root of the fuel head pressure multiplied by the density of the fuel. So we really need to know the weight of the fuel flowing through a jet to understand all this. Now to further confuse the issue keep in mind that air/fuel ratio is based on weight of fuel and weight of air, but jets essentially meter by volume. 0008' (I'll let those so inclined do the math to determine the flow difference). Keihn jets are numbered by jet id, and the difference between a 178 and a 180 is about. The flow difference between a Mikuni 175 hex jet and a 180 is about 6cc ~3%). Mikuni hex head jets are numbered by bulk flow, while Mikuni round head jets and Keihn jets are numbered by inner diameter in mm. Well, Once again Help will be greatly appreciated. Surely there is a chart out there somewhere that someone has formulated for this (I Hope).

#Mikuni pilot jet sizes how to#

420' and you'll see what I mean) Sooo, Can anyone enlighten me as to how to know what size drill I need to goto a 470 then a 480 then a 490 etc. My reason of writing is to try to find out what these numbers mean (420 cannot be Thousands of an inch, Get a vernier caliper and open it to. Plus if it were an airleak causing this then I think it would make the 'ying ying' sound and it would be lean from bottom to top NOT just on the top end right?, Right? I can get the low to mid jetted OK but if I get it on the pipe (Main Jet) It gets WAY too lean, Everyone keeps telling me Ive got an airleak or something but I dont buy it (Or see it) everything is clean and dry including under the LH Cover. Im jetting my 01 CR250 and have ran out of sizes of main jets so Im afraid Im going to have to resort to drilling one out (Just for this weekend 'till I can get more sizes) Im up to a 460, Stock is a 420.