95 and Earlier Model
CV Carburetor Modifications

If you are an owner of a stock late model Harley-Davidson you may have noticed that it does make all that much power for all that displacement. There are many reasons for that fact, many of which you can't change. Luckily there are a couple things you can do to get some some significant increases in HP without laying out much cash. Here is what you need to do to create your own basic 'Stage 1' engine.
If you have a 1996 or later model CV carburetor and do not want to change the OEM needle, additional jetting information has been provided to Motorcycle Performance Guide that should improve the performance on these bikes. If you have one the these later model bikes, go to the 96 and later CV carburetor modification page

MAKE IT BREATHE:
Fundamentally, what you want to do is get more air into the engine and allow more exhaust to get out. To allow more exhaust to escape the engine you'll need to punch the baffles out of your stock exhaust system, or get a set of better pipes. A word on pipes. Straight pipes may look and sound good, but this is not the best setup for a street performance engine unless you are willing to give up Torque and useable HP. Straight pipe will not give horse power readings greater than other pipes and the power band created by this type of exhaust system is very narrow. It will not win you any stoplight Gran Prix's against a similar engine with well designed pipes such as SuperTrapp, Python, Rich Products, Bartell, Vance and Hines, or even the H-D slip-ons. You make the decision. Follow the pack or make it Fast.

Step One for getting more air into the engine is to first get more air into carburetor. That means buying a high-flow air filter element like those made by K&N. The Screaming' Eagle brand is as good as they get, but most after-market companies also offer them. K&N now makes a replacement for the stock air filter. If you use this filter element, you will need to add holes in the plastic air cleaner cover. Do this by drilling a series of 1/4" to 1/2" holes in the plastic cover. This will improve the air flow to the filter element.
Step Two is to make changes to the stock Harley-Davidson CV carburetor. That's what these instructions are all about.

This step-by-step instruction are a consolidation of articles and information from Mark "Tusk" Amos, Charlie "Hacker" Powers and Steve 'V-Twin Cafe' Mullen. These techniques were used in the V-Twin Café Stage One Basic Engine Development. It's easy and it works. The techniques described here were gleaned from:

Do not under-estimate the ability of the stock 1990 and later Keihin CV carburetor to produce good power. The stock CV carburetor has a venturi diameter of 40mm (1.575 inch). Properly tuned, a CV carburetor is capable of supporting 80+ horse power in modified engines. A well tuned, stock cam late model 1340cc ( 80 CID) can develop up to 61 horse power with a modified CV carburetor. Look at the V-Twin Café Stage Three Round One Engine development. The engine combination listed here produced 81 HP with 85 Ft.Lbs of Torque. The same engine combination with a Mikuni HSR-42 produced 85 HP. This is not a significant difference for a street engine. Review the Dyno run results for yourself.

Parts needed:
27094-88 Main needle ('88 XLH part) Lowers MPG
Or shim the stock needle with 2 - #4 washers
27116-88 Main jet (#165)
27170-89 Pilot or "Low speed" jet (#45)

Tools needed:
Drill
1/8" bit (.125 inches)
1/16" (or approximate) bit
Hand tools for removing and disassembling carburetor
Good quality fine flat metal file (i.e. Nicholson)
400 or 600 grit emery paper

Remove the carburetor per your service manual. You MIGHT get away with leaving the throttle cables OR the choke connected to the bike, but don't count on it. It would be much easier if you remove the carburetor completely and go to a work bench. I usually lea