My wrench says he can make a stock Keihan CV carb perform as well as
anything else. In this I do not doubt him, as he races a CV, but I do
wonder what he would charge. Unless you are a carburetor wizard or are
limited by a sanctioning body, dump the stock carb if you want to do anything
more than wake up your motor.
There are several good carburetors on the market. Mikuni is recommended
by many wrenches, but is made overseas (hssssss). They do sell a hell-of-a-nice
Two that are made in the US are S&S and Quicksilver. Because of its
popularity, the S&S is well known by every Harley mechanic and has
excellent parts availability.
The Quicksilver carburetor is much newer. Its advertised benefit is its
simplicity. Jeffery Stubbins reports that the milage is greatly improved
over stock, stock w/Dynajet and the S&S. This carburetor is California
Air Resource Board (CARB) approved. Its reputation is growing rapidly.
I installed a QS (4mmm I think) on my Dyna. Because I live in California
I had to order the 48 state needle separately but once installed I loved
it. If it's simple enough for me, it's simple enough for yoy.
"I ran the 38mm QuickSilver on a FTLCU with a Crane 316-2b and the
Thunder header. It work flawlessly. Was able get 73 HP to the rear wheel[.
T]he throttle response was great. Was a breeze to tune just put it on
the dyno to choose the proper needle (could be done by reading the plugs
but the dyno was more fun) then run it down the road a 2000 rpm and
check the plugs to adjust the low end. There is only three adjustments
total on the thing. The needle sets the mixture above 2500, the click
adjustment sets the low speed mixture and you just set idle speed like
any other carb.
I liked the carb so much that when my engine gets back with the 96"
kit in it I'm putting a 40mm QS on it. Of course the fact it supports
the cruise on my Ultra doesn't hurt either." -- Leonard Pennock
CV Carburetor Hop-up
The following was provided by Leonard Pennock as...
"...a very inexpensive hop up of the Stock Keihan CV Carb used
on the late model big twins. The information for this was extracted from
an article that appeared in the December 1994 issue of American Iron and
an article that appeared in the premiere issue of Thunder Alley. These
changes are only legal for offroad use (then again so are pipe, carb,
and cam changes). Refer to the harley shop manual for your bike for disassembly
instructions of the carb.
There are three things that need to be done for the low dollar hop
up of the CV carb. The first is to provide access to the idle mixture
screw. This is done by using about a 1/16" drill bit to drill the plug
that is covering the idle mixture screw on the bottom of the carb. After
drilling the plug insert a sheet metal screw and pull out the plug.
To adjust the idle mixture warm the bike up adjust the idle speed to
1000 rpm screw the idle mixture in until the motor starts to stumble
and then back it out 1/2 turn. Then reset the idle speed back to 1000
The next area that needs attention is the hole in the base of the slide.
This is the vacuum port. Drill this hole out with a #30 drill bit (.128").
This will improve the responsiveness of the slide and will also richen
the mid range slightly.
While the slide is out of the carb it is time to consider replacing
the needle. Most of the CV carbs have a needle that is fat for about
half the length which causes the CV to run lean in the mid range. The
idle needle has an even taper and was used in the 88 49 state Sportster
and is part number 27094-88.
The next and final area of the low cost hopup is the carb jetting.
For a slow jet use a #45 part number 27170-89; however, occasionally
for engines with real hot cams it may be necessary to go with a #48.
For the main jet start with a #165 part number 27116-88 which should
be correct for most bikes. Some times it might be necessary to run a
#170 but this is the exception not the rule. Read the plugs and use
the dyno to find out for sure.
This completes the low dollar hop up. The total cost of parts should
be under $20 but since I didn't price them I'm not sure.
This will give the CV a much better response and is really all the
money that should be spent on one in my opinion. If you want more performance
go with a good carb like the Quicksilver, S&S, Mikuni or Rev Tech
and put the CV on top of a stack of papers (it works good for holding
the manual open)."