The CV40 is a good
carburetor; we've had numerous customers break
100rwhp using a stock, rejetted CV. Likewise, the
Mikuni HSR42 is a popular aftermarket carburetor
used on many high performance projects.
We often get asked if the Mikuni is needed or worth
the money. Well,
on several occasions we've dyno tested the CV against the
Mikuni HSR42. Here are the answers.
On a mildly modified
bike like this one (883 to 1250 conversion with
stock 883 heads), the Mikuni just brings a little
bit to the top of the dyno sheet. We've seen this
result over and over, anytime we test it on a mild
bike, it's hard to justify the cost of the Mikuni
with the dyno sheet.
When the mod level goes
up, however, the story changes:
This motor has a 1250
kit and a set of Stage 2 '04 XL1200 heads, as well
as a set of SE .536 cams. The gains are still at the
top of the dyno sheet, but picking up more than 5hp
at this level is HUGE, and it's some of the cheapest
horsepower you can buy.
What the dyno sheets
don't show you is that in either case, the Mikuni gives
noticeably quicker throttle response. Twist the grip
and the motor reacts right now, giving the
impression that your wrist is connected to the rear
wheel. Also, the Mikuni is a tuner's dream, it's
main jet is accessible in seconds via a plug on the
bottom of the carb, instead of being a 20 minute job
as it is on the CV. There are a lot more
adjustments available on the Mikuni and although
they're dialed in very well out of the box, the
obsessive tuner can really get one perfect
with all the adjustments available to him. So even
if your bike is mild and your dyno sheet
doesn't stand to benefit a whole lot from
a Mikuni, it may be a worthwhile investment anyway.
I've never heard of anyone who bought a Mikuni and
What manifold do you need? Well, a
Mikuni HSR42 slips right into a stock CV40 manifold.
Eagle manifold is also available to accommodate the
HSR42, and it comes with an additional rubber booty
to allow the fitment of an HSR45 or CV44. But do you
need this manifold for the HSR42, or will the stock
one work just as good?
As luck would have it,
we've tested the HSR42 with the SE manifold against
the stock manifold, multiple times, and each time
the SE manifold brought nothing to the party; save
your money, you don't need it unless you're using
the HSR45 or CV44.
With the CV air cleaner
adaptor installed, the Mikuni's air cleaner surface
ends up in the exact same place as the CV's. A
standard carb support bracket made for a CV works
fine, and everything bolts right up. Late model
Mikunis even work fine with your stock throttle
cables. About the only thing you may have to do is
clearance the top fin on each cylinder just a
little, you're more likely to have to do this on
aftermarket big bore cylinders. But overall,
installing a Mikuni is largely a "bolt-on"
Mikuni carburetors are readily available from NRHS,
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