Thursday, June 24, 2010

Making It My Own: Part 2 - Modifying the Carburetor

Before I bought my Harley, some guys I ride with tried to steer me toward getting a bike with fuel injection, but I was leaning toward getting a carbureted bike because it is simpler. Since I have trouble programming a VCR, I would rather fix something mechanical than computerized or electronic.

Some Harley owners ditch the stock carburetor for an S&S or Mikuni carb, but the factory Keihin CV carburetor is a simple, reliable, time-tested design that makes plenty of power for stock or slightly modified engines. The carburetors are set lean from the factory, due to EPA restrictions designed to reduce exhaust emissions. But, that results in drivabilty issues, such as the engine taking a long time to warm up; poor cold-weather performance; and an annoying tendency for the engine to stumble and 'cough' through the air cleaner when giving it a slight amount of throttle while cruising. This was a real bummer on group rides especially, and it also made me less confident riding the bike.

As always, I did a lot of online research before ordering a Stage 1 carburetor kit made by CV Performance (I ordered the kit through Besides main and pilot jets, and hardware, the kit includes an improved-design slide needle, slide spring and emulsion tube. I also ordered the optional EZ-Just idle mixture screw, acclerator pump nozzle and a new fuel inlet elbow made by CV Performance. From my local Harley dealer, I bought a float bowl O-ring; a carburetor-to-intake rubber seal ring; and a chrome top cover to replace the stock black plastic cover. I also bought a couple feet of 1/4" rubber fuel hose. With a factory parts and service manual, plus the instruction sheet from CV Performance, I was good to go.

After replacing my exhaust system first, I removed the carburetor, which came off quite easily. I am blessed to rent an apartment with a clean, well-lit garage and a workbench and stereo. Using my 'shop,' I took my time and disassembled the carb, spraying it with carb cleaner as I went along. The CV carb really is a simple design and I had no problems taking it apart or putting it back together. The only "oh crap" moment I had was when the EZ Just idle mixture needle fell off the bench and landed on the concrete floor with a "ping," but it didn't appear to be bent or otherwise damaged, thank God. (The only other glitch was that the carb cleaner discolored the plastic enrichener knob, but I can always get a chrome cover for that.)

The job went quickly, since I was able to save a few steps. For instance, I did not need to drill out the plug that the factory uses to cover up the idle mixture screw, since someone already did it previously. Also, I decided to leave the stock fuel inlet elbow, since it was already an all-brass piece (some of the stock fuel elbows are part plastic). While the instructions with the CV Performance Stage 1 kit were adequate, I do have a complaint with that company because there were no instructions with the EZ-Just needle or the accelerator pump nozzle. I suppose the needle probably doesn't need instructions, since it just screws into the carb, but I decided to leave the stock accerator pump nozzle since the new nozzle had no directions and I had no clue how to remove the old nozzle.

When re-assembling the CV carb, perhaps the most critical part is making sure the slide diaphragm is not pinched. I used a bit of petroleum jelly (actually, stuff used for spark plug boots) to hold the diaphragm in place, and it worked like a charm. After re-installing the carb and replacing the fuel hose, I struggled a bit reinstalling the throttle and idle cables, so I opened up the handlebar switch cover and disconnected the cables from the handgrip. I also used this opportunity to lube both cables, then adjusted them.

Next step: installing a high-performance air cleaner assembly.

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