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]
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.