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Adam Fuller's account of how he installed Mikuni VM 34mm carbs on his XS650
I bought
the carbs from Halco as a complete kit which includes a new throttle cable
and foam *RamAir* filters. The kit costs about £350 including Vat. This
is not cheap but I had so much trouble with scabby ancient carbs and the VMs
are supposed to give much better mid-range I bit the bullet and bought them
when Halco were offering a *10% winter re-build discount* in January 2003.
Another benefit to converting to these carbs is that they get rid of the incredibly
fiddly OE Yamaha air boxes which are, in my opinion, a right pain to get on
and off.
The kit arrived and the carbs certainly look the business, they have a little sticker on the side saying *not for aircraft use* which is cool. I think. The throttle cable setup is in three parts, a single cable from the throttle to a junction box under the tank then two cables from there, one to each carb. Ok that's four parts.
I ran the cable from the throttle under the tank and have the junction box on the right hand side of the frame tube, this seems to work fine with no snagging of the cable and no pulling as handlebars are turned.
I had opted for inlet stubs with take-offs to allow you to fit vacuum gauges to balance the carbs, these never come from the manufacturers with caps to blank them off so I decided to join them together with a length of fuel pipe which seems to work OK. I have secured the pipe with jubilee clips as a belt and braces measure. 8mm ones from Halfords fit.
The manifolds bolt straight on, I re-used the existing gaskets because they were in good condition and a little thicker than the ones in the kit. The ones provided are genuine Yamaha though so if your old gaskets are cream crackered I would not worry. Also the ones in the kit would have needed a little fine tuning with a scalpel as they were a fraction too small ID and would have created a small *lip* in the inlet.
The carbs come from Halco with the jet size and needles already set up so no need to change anything there or fiddle with any settings.
The throttle cables are easy to fit to the junction box, I had to file a bit of solder off the ends to make them fit perfectly.
To connect
the cables to the carbs you have to unscrew the tops of the carbs taking care
not to send the throttle return spring that lives in there flying across the
workshop. This spring is also known as a pingfuckit*.
Its pretty easy to see where and how the cables connect to the top of the
throttle slide.
When fitting the carbs you will need to make sure the top of each carb is fully screwed down or you will end up with no play in the throttle cable. Do not over tighten though or you will crack the carb body and you don't want that.
Fit the carbs to the manifolds and tighten up the jubilee clip that holds them in place.
Finally fit the foam air filters, they do not come oiled and there is no oil supplied so I guess they don't need it. You can get air filter oil from car accessory shops, even the dreaded Halfords.
I found that my metal side panels fouled the pod filters so a pair of pliers was used to flare them out slightly. My bike is missing the little rubber dampers that fit over the side panel lugs on the frame. If you have these then the side panels will sit a little further out from the bike and probably not foul the filters. I have ordered the damping rubbers they are still available and are about £1.30 each*.
I took the opportunity of fitting new fuel line, I bought a metre of it from Halco and its better quality than you usually see. I used new jubilee clips here too.
The new carbs have a choke lever on the left carb and a lift up knob (tee-hee) on the right. After a couple of goes on the kick starter the bike started and sounded fine, after warming it up I backed the idle screws off ¼ turn to slow the idle a bit.
A quick short test ride confirmed everything OK although I have yet to test it on the open road.
In other words its really easy to do!
