How to ID and overbore stock carb main jets

[noiseguy]

From www3.telus.net/dougsimpson/Elite_1.html

Included with edits. Describes how to redrill stock jets to larger sizes. I would still recommend buying the right jet, so that you don't have to keep track of what size the jet actually is after you overbore it. Maybe file the number off and rescratch it in. Someone had asked about this previously.

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I had ordered another main jet from Honda in the same size I had as they don't offer an oversize jet. The idea was that I would drill the new jet until it was obviously too big and then I could go back and drill the original jet to one drill size smaller, hopefully the "right" jet size. My jet (1990 Elite 50) was stamped with an 88 which I finally figured out meant it was 0.88 mm. I figured this out by comparing some guitar string sizes against my main jet. The strings carry metric as well as imperial measurement so I noted which of the various strings would fit through the main jet opening. My D string (.711 mm) would fit but my A string (.965 mm) was too big. The chart below shows the various number drills that will increase the scooters main jet size.

Jet Number Drill Size Imperial measurement Metric measurement
63 72 .00208 inch .6350 mm
66 71 .00217 .6604
71 70 .00233 .7112
74 69 .00243 .7417
78 68 .00258 .7874
81 67 .00267 .8128
84 66 .00275 .8382
89 #65 0.0350 inch 0.889 mm
91 #64 0.0360 " 0.914 mm
94 #63 0.0370 " 0.940 mm
97 #62 0.0380 " 0.965 mm
99 #61 0.0390 " 0.990 mm
102 #60 0.0400 " 1.016 mm

The (1990 Elite 50) stock main jet is just a small amount less than a #65 drill so it would make sense to start with a #64 drill and work towards the larger sizes (larger holes; the number drill sizes get smaller). A word of caution here before you start. The richness or leaness of your mixture can also be affected by a number of other factors so make sure these other parts are operating to specs before you start drilling.



--- Edit - 04/29/2010 mousewheels : The table is incorrectly showing the diameter in the "in" column for jets 84 and smaller. Here's a corrected version: