quick 'n dirty - like it!

but i'm not so sure how accurately repeatable that method is for tuning...

I thought I took more pics but here is what I ended up with, not pretty but it works well.

 

Where did you source your jet drills?

Ebay, I think they were about $30 the metric drills are in the blue kit and the imperial drills are in the handle of the hand drill.

 

Thanks

Slight caution here. I purchased a set of metric mini bits locally at KMS tools, came in an identical but orange case as granny's blue ones. According to my caliper, they are all about .03-.05mm smaller diameter than the advertised size on the box.... Maybe its my caliper, but it also was "confirmed" by comparing to a set of brand new 160 main jets that the 1.6 mm bit went right into with a quite a sloppy fit....

I guess the point here is, if your trying various jets in a tuning session, confirm the change in size from set to set via comparison to a known standard, don't think that going from a factory 160 to a you-drill 150 will actually be taking you down by .1 mm. You may be surprised at the result.

Jim,

Thanks for that. I was wondering about the exactness of these sets and how to source them.

Slight caution here. According to my caliper, they are all about .03-.05mm smaller diameter than the advertised size on the box....

 

Drill bits produce a hole larger in diameter than the bit itself. And the worse the drill is produced, the more poorly the two cutting lips mismatch, the larger the hole (within limits) it produces.

 

Those drills that measured undersize when static may actually produce the advertised correct size hole! Only real way to know for sure is to use the bit to drill a hole and then use pin gauges to check the hole size.

Soldering aluminum pin gauges in situ then pulling may be a nice technique.

or if you can get some accurate gauge wire that you can solder in and pull out. you might need to dress the top of the solder lightly to remove the lip/burr but you would def. get a better measurement than drilling. looks like your mini-bits use a hand twisted drill, which might be difficult to get a very straight, clean bore. these are all tiny nits we're picking, but it would suck to do all that work just to find out you were 1/2 a jet size off due to drilling inaccuracies...