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Old 01-28-2013, 07:50 AM   #728
Professional Idiot
Joined: Dec 2010
Location: Deepest Southern France
Oddometer: 125
External choke progress

thought I owed a bit of an update on my progress with the external choke set-up. The news is mixed. All is installed and functioning reasonably well with adjustable fuel and air jets. Here's a general view of the installation:

The horizontal aluminium cylinders with the square bases are the mixing chambers and control valves, showing cables exiting at the left hand side... you can just see a brass adjuster for one of the cables... which are controlled by the OEM lever and some custom-built cables. The two throttle valves in the foreground are the air inlets which are plumbed into one of Chris' velocity stacks (which are FANTASTIC pieces of kit by the way Chris... many thanks!!):

At the base of each aluminium cylinder is the fuel inlet (small-bore tube), each fed from the float-bowl of the respective carb., again with a throttle valve in each feed:

On the far side of each of the aluminium cylinders are the mixture outlets, each feeding to the existing inlet vacuum-port tapping (normally blanked with an M6 screw), the fitting containing an emulsifyer jet (actually an FCR idle jet!!) which pokes into the inlet tract:

I'm still far from content with the solution as each time I start the bike I need to fiddle with the jet settings for it to fast-idle well on choke. I suspect that the outlet from the mixing chamber is just too far away from the inlet port; sometimes I get a well prepared mixture, more often it all condenses back to liquid interspersed with air bubbles.

My next step is to mount the mixing chambers directly to the inlet port tappings to try to avoid this, then maybe play around with the size of the injection jets a little.

I'm convinced this solution will work well once I manage to dial it in correctly. The only question is if I'll finish before the decent riding weather arrives... at which point all bets are off as I'd rather ride, despite this turning into an interesting little project.

I'm still watching and waiting to see how the internal choke works out too. No doubt it'll be a much more elegant solution than mine.

Cheers... Paul
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