While trying to eliminate the sneezing and backfiring
problems I was having with my new 800 Classic,
I found that a 1/16" shim under my needle seemed to cure
my problems. When I posted this to the internet, a few people
emailed asking specifics on how to do this. They also
mentioned not wanting to change pipes, etc. This got my
curiousity up a bit.
Since I was waiting on a set of full length heat shields
for my Cobra Classic Slashcuts, I was back on the stock
pipes. I'd been reading about the CV carb tuning procedure
on the biketech website at
http://www.nightrider.com/biketech/carbadjust.htm.
They mentioned that you should idle the bike as low as it would
go, then "tweak" the low speed needle for peak rpm, and
blip the throttle. Open the needle in 1/4 turn increments
until the bike no longer "sneezes", or some such. They
cautioned that poor fuel economy could occur if this
proceedure isn't followed and the low speed circuit was
unnecessarily opened too much.
Since I'd been cranking the screw out to 3 turns and
letting it fly, and since I didn't really know when I'd
reached the peak RPM range because one has to take so
much stuff off of the stock setup each time to make the
adjustment, I decided to fabricate a remote method
to adjust my low speed (pilot) needle.
Below is a picture
of my remotely adjustable low speed needle assembly. This
picture was taken from the left side of the bike, looking at
the bottom of the carb bowl when it extends down below the
"Y" intake manifold. In the picture, my finger is holding the
fuel line to one side. Do you see the remote needle? It's the
black hose in the left center of the picture with the spring
clamp around it. Fabrication was easy. I drilled the plug
that covers the low speed needle, removed the needle, and
soldered a piece of brass stock to the "head" of the needle
where the screwdriver slot is. I then pushed a short section of
flexible vacuum tubing on the brass stock and secured it with
a spring clip I had left over from the EPA system removal. I
reinstalled the needle in the carb, and routed the hose out below
the air cleaner cannister and cut it off so only a short piece
remained (but was long enough to grasp).
![[vulcan pic]](bike20.gif)
I then removed the 1/16" shim I'd stuck under the needle
and re adjusted the carb's low speed circuit according to
CV's recommendations. (By the way, my low speed needle was
only backed out from "closed" 3/4 of a turn from the
factory!!! Damn, I couldn't beleive it!). Wow...no backfires
or sneezing. It's still a little cold natured, but once warmed up,
she runs like a champ. With the 1/16" shim back in, I only
need the choke to start it, then shove it in and go.
My "gut" feeling, based on CV's procedure and the results
I got, the needle shim isn't necessary with the stock intake, airbox,
and pipes. With my low speed needle set at 3 turns out, it
idles and runs great into the factory pipes. The fuel economy
is barely changed, and it still gets over 50 mpg.
I think, for those with the stock setup, I'd knock out the
plug on the carb that covers the low speed needle and crank
it out to three turns and ride. Maybe, the remote
needle adjustment mod I made might allow you to tune it
perfectly for your altitude, but I don't know how much
affect altitude has on the stock system.

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Stuff about Tweek's Bike
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