Yep. I drilled mine per his great instructions
Would you be willing to share your information and any tips?
This involves drilling the little holes in Keihin's "needle jet holder" (which holds the needle jet up inside the carb's throat) that everyone else always called the 'emulsion tube' out to a little larger size. There are 2 sizes of holes: the upper RPM ones are smaller at about 0.025" and are OK: it is the lower RPM ones that became an issue, more so as gasolines became more refined as our EPA got involved with their recipes. At first (1969) the 750K0 sandcast and early [prior to about 8/69] production 750s came with #120 mainjets and aeration holes of size 0.0325" in the lower positions: this proved to not aerate the gas very well and above about 1000 feet altitude would foul the stock D8ES sparkplugs in a week of city riding. To help solve this, Honda did several things, which in order to the K3 were:
1. Reduced mainjets to #115 by about 10/69 builds, then to #110 in the K1 (657A carbs) and #105 in the last few months of the K3, which became standard after that.
2. Opened up the tiny 0.0325" aeration holes to 0.035" around 12/69 or so, then to 0.0375" in the 657A series carbs (K1 bikes). Most knowledgeable wrenches would open them up again to 0.039" with the advent of MTBE added to our gas, and ethanol requires the same. Here in Colorado, the holes can be found bigger than that, but it doesn't seem to matter beyond that size.
3. Altered the airbox by reducing the inlet slots by about 25% overall by the early K1, at the same time the bowl vent tubes were dropped from 1-per-carb to 2, sharing the 1-2 and 3-4 carbs for each of the 2 vent tubes. These hoses were also made about 5 cm longer in this change, to reach further behind the airbox for still, quiet air to feed the carb bowls.
Generally, opening the larger (lower RPM) emulsion tube aeration holes to 0.039" in the K0, and dropping the mainjet by #5 size if it is/was #120, usually helps a lot with today's gas.
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Edit: my apologies to those who read my earlier version of this that mentioned the "upper" and "lower" holes without the RPM note, and the location. I was talking with someone at the same time about other things while typing, and my cut-and-paste got lost and out of hand!
The upper RPM holes are the lower ones (smaller, toward the bottom of the bowl) and the lower RPM ones are the upper ones (toward the carb's body).
---for those of you who remember 2006 when the book was cooking, the 6 weeks of "no news" about it at the end of writing and before publishing was the time I spent going over those pages, looking for dumb errors just like this this one was...
