Does anybody recognize the branding mark on those jets?

 

That is actually a K for Keihin.

 

If you have a drill set with drills (fraction or number) small enough to find the largest size that will fit in the jet, your dealer should be able to use that to find the next larger size jet. I've even drilled out a low speed jet, but I'd get the correct one up size first if you could, and that shouldn't be a problem for a Harley carb.

 

42 pilot = .0165"
45 pilot = .0177"

 

These jets cost a few pence each (around 7 bucks), so I wouldn't mess about any more! 98hotrodfatboy suggests a 45, so simply buy yourself one that size, so you know where you are for any future changes required.

 

Just back from my local HD. All they had in stock was a #45. They told me #48 is the stock size (which I found baffling). However, 45 is where I was planning to start so here we go. Now I just have to battle the heat in my garage on this 108 degree northern California day. I'll let ya'll know how it goes. Thanks again for all the help. You guys are great!



This is inner or outer diameter? I'm getting something quite different:





Drill bit for comparison. Not a bad idea. I don't think I'd mess with drilling them, but for comparison; I'll keep that in mind.

 

Wait a minute here. We're talking about the size of the little holes on the shaft/tube aren't we?

 

Use the drill bit as a gauge only to determine the ID, with the plain end, not the sharp bit. Better still, as these things are high precision and pretty critical, leave the poor jet alone! No need to know the diameter if you know its size.

 

I get that, but what hole am I measuring. Inner diameter of tube or diameter of little holes in the tube? I'm guessing little holes in the tube?

Upon visual comparison the unmarked one I pulled out looks exactly the same size as the #45 I bought today.

 

You are not going to be able to tell the difference in size by the naked eye... Just put the known 45 in and go from there.................. You need a starting point...........................

Just so you know it's always the inside diameter of the tube and not the little holes........ K? Actually it's not the tube but the little pilot hole where the screw driver seats into it....