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Classic Bike Trackdays

SDR200 cable-operated choke conversion

 
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James P



Joined: 31 Mar 2013
Posts: 109
Location: Sydney, Australia

PostPosted: Sat Oct 17, 2015 5:43 am    Post subject: SDR200 cable-operated choke conversion Reply with quote

Although I generally like to keep things simple, I also like to have ready access to the choke control. Anyone with similar requirements may like to consider this conversion:


This is the left-hand switch block from the SDR200 and a choke lever assembly from an FZR250. Coincidentally, the holes for mounting the choke lever assembly (B) align perfectly with the bosses on the underside of the switch block (A).
All that is required to mount the choke lever assembly is to drill holes through at A and tap M3. I'd definitely recommend removing the internals from the switch block first, to save them from damage or accumulation of swarf. Use M3x8 pan (or similar) head screws to secure the choke lever housing to the switch block.


This is the assembly mounted on the bike. Unfortunately, the cable entry angle for the choke lever housing is not ideal, meaning that the cable would be kinked slightly where it passed the fork stanchion. Although it would probably be OK in practice, I used a Venhill FB9 elbow/adjuster to keep it well clear. The FB9 needs shortening where it plugs into the choke lever housing (I cut it down to 7mm).
I made the rest of the cable using other bits from Venhill (LB1TS conduit, R77/1 wire rope, 2x F1 ferrule, nipple BN608 for lever end, nipple EE7 for carb end). At the carb end, I used a standard TZR250 1KT choke boss, spring and plunger.


This is the steering at full lock to the left. There is plenty of clearance between the choke lever and fuel tank. I've got the cable adjusted so there is some free play in it for the full range of steering movement (i.e. turning the handlebars will not operate the choke!).


These are the ends of the cable. Outer conduit length is about 740-750mm, including ferrules. With the cable on the bench (i.e. off the bike) and the adjuster set on minimum, the maximum free length of cable at the carb end is 52mm (not including the 3mm long nipple). The adjuster does give some margin for error.
The FZR250 choke lever offers about 23mm linear displacement of the cable, but the plunger in the carb needs only about 13mm. Thus, the lever travels only about halfway in use.

This particular choke lever assembly came from an FZR250 2KR. As far as I can tell, the FZR250 3LN choke lever is practically identical. My research suggests that the following FZR choke levers are also suitable:

FZR400 1WG
FZR750 2LM
FZR1000 2GH, 2LL, 3GM

There are likely other Yamaha choke lever assemblies (FZR or otherwise) which would also work. However, if carrying out this conversion, I'd suggest doing your own research before buying any of the 400/750/1000 choke levers though, just to make sure they will fit!
I briefly considered using the similar but different NSR250 choke lever on the right-hand switch block, but it wouldn't be as neat and easy as the FZR250 choke lever on the left.

While I was at it, I also made myself a new throttle cable. I'll be using pre-mixed fuel & oil, so the oil pump and YPVS motor portions of the standard throttle cable assembly will be redundant. I've been able to reduce some of the clutter under the fuel tank by using a single cable from the twist-grip to the carb.

Regards,
James
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