96 and Later Model
CV Carburetor Modifications

Changes improve the performance of your late model CV carburetor are easy to perform. This is another variation of the CV carburetor modification that does not require the OEM needle to be replaced. Here is what you need to do to create your own basic 'Stage 1' engine.
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, re-jetting the carburetor to improve the air-fuel mixture and increase engine power. That's what these instructions are all about.


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 64 horse power with a modified CV carburetor.

Parts needed:
27114-88 Main jet (#180)
27170-89 Pilot or slow jet (#45)
Late model bikes may run better with the #48 slow jet.
1/8" Thick small washer

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 leave the choke cable hooked to the carburetor and disconnect the pull-handle end, taking the entire choke cable/carburetor assembly with me. Your call.

IDLE MIXTURE ADJUSTMENT:
Before we really get started, you might as well remove the aluminum plug covering the idle mixture screw. Using about a 1/16" drill bit, turn the carburetor over and CAREFULLY drill a hole in the small plug just on the motor side of the float bowl. If the plug did not fall out when drilling, remove your drill bit and use the back side to pry it loose. Some carburetors may require the CAREFUL insertion of a self-tapping sheet metal screw the get a good enough grip to pull the plug.

Underneath you will find a slotted screw. Turn this screw clockwise until GENTLY seated...jamming the screw down too tight will ruin both the carburetor and needle. Now back off about 2 1/2 full turns. This gives you an approximate starting point for tuning.

SLIDE MODIFICATIONS:
Remove the top of the carburetor (slide vacuum chamber cover) being ca

 

Is there a finish to this thread?