Evolution Road King

Garage time with the old Harley.




 Amongst other things, the carburetor has been dissected.

  Replacing it with the ever popular Mikuni was considered, but after a lot of reading, the realization that the stock unit performs exceptional under a variety of conditions has materialized.

The Mikuni does have an edge, especially if you build a radical engine, but considering the price and my plans of a relaxed riding style with this bike it is not necessary at this time.

First thing was to note the current state of tune of this Keihin CV (Constant Velocity) Carburetor and compare it to the sound recommendations that have been gathered and decide if any course of action needs to be taken.

 A lot of Harleys on the road are over jetted and running excessively rich, gaining no more power than a properly jetted bike and compromising fuel economy and range.

 This is what I found -

#42 Pilot Jet is stock.

#180 Main is stock

Needle has been replaced with an adjustable unit and the clip has been placed in the 3rd groove from the top with a thin washer shim under that.

Slide hole has been enlarged to 9/64th".

Air/fuel mixture screw has been uncapped (factory tamper proof cap removed) and turned out 3 turns.

Well, the bike was running and starting exceptional, and these findings are pretty much in line with what the guru's have suggested, so they are going to remain intact.



 The #42 Pilot jet is a tad on the lean side, but the mixture screw backed out to 3 turns, which is max, makes up for it. Those two things control the idle circuit.

The main jet is fine. The consensus is that stock Harley main jets are if anything, too rich.

But the most important mod is to replace the needle with one possessing a more efficient taper and a richer condition off idle to eliminate any stumble or flat spot; Better drive ability.

 Wide open, which is primarily the main jet, is fine. EPA doesn't test at WOT, so the factory can install a rich main jet.

The enlarged hole in the slide is controversial, arguments from both camps are mixed - to drill or not to drill.

 The intent of the enlarged hole is to receive a stronger vacuum signal on the slide, thereby obtaining a quicker throttle response.

 Some swear by the results while others say it creates unwanted oscillation in the slide , less fuel economy and negligible, if any, benefits.

 Supposedly lighter bikes benefit more greatly.

The slide is already drilled so it will stay, but if starting from scratch, I would probably opt not to.



While removing the fuel line from the carburetor, the notorious two piece metal and plastic elbow broke. That is fine, as it needs to be upgraded to the newest iteration anyway.

When ordering, the new factory part is all metal.

But, the remaining metal stub must be removed from the inlet. The best method to achieve this is to run a 1/4-20 tap into it creating threads within the ID and then assembling a makeshift puller with a 1/4-20 bolt, washer and socket.

Once removed though, the carburetor must be cleaned thoroughly and blown out with compressed air to ensure no debris remains.

No problem, as I perform these actions as part of the carb service regardless. Then after slightly starting the new fitting by lightly tapping it and ensuring it is square, a large vise presses it home efficiently. You must ensure the 90 degree fitting is oriented properly to accept the fuel line routing before pressing. You only have one shot at this.