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Mikuni VM36

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  • Mikuni VM36

    If I have to move away from the GP2 carburetor, I am thinking of the Mikuni VM36 which can be supplied by motocarb.co.uk jetted to suit the Silverstone. Has anyone used this setup please?

  • #2
    The first time I gave up on a very worn GP I fitted an ex-TZ 34mm VM. I was a little concerned about the carb downdraft if I fitted the VM directly to the cylinder, ala GP, so I made an aluminium adapter to reduce this to a similar angle to the VMs on my Yamaha TD2B (20 deg. if I remember correctly). An adaptor is require anyway because the studs on the GP are on different centres to the Mikuni rubber mounts. I used this set-up for many years but then tried the GP again for one season after buying replacements for all the worn parts. While the top end was better, I could never get it to carburate cleanly in mid-range.

    At that point I decided to buy a 36mm VM as I figured it would probably flow a similar amount on full bore as the "smooth bore" 1 3/8", 35mm GP. I bought the carb from motocarb and had them machine the horn off the intake and fair in the carb intake to match the TZ (and TD2B) carbs. At the same time they fitted a UFO in the bottom of the slide to smooth out the air flow. This set-up worked straight out of the box and the jetting they provided was very close. They also provided a couple of jets either side of those fitted to fine tune the carburation. I have used this carb for several seasons of racing now. I highly recommend this company.

    They may have some suggestions about fitting the VM directly to the cylinder at the same angle as the GP and whether his would be OK, given that some provision has to be made for the different stud centres.

    Stan

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    • #3
      Hi Stan - thanks, I'll be ordering mine tomorrow. As a matter of interest, does the VM allow the engine to tick over a bit better in the warm-up area as the GP clearly does not? Rene

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      • #4
        Hi Rene, The VM does have a throttle stop screw, unlike the GP which was manufactured for racing, so I suppose it could be set to allow a tick-over. However I have always set up my carbs to close completely when the throttle snaps closed on release, as required by our rules. In fact, the original VMs on the TD2B and the TZ do not have a screw to allow holding the slide partly open. My thinking was that this requirement was so that the motor shuts down if and when the rider parts company from the bike. Hopefully this also eliminates or reduces the amount of dirt the motor ingests when it is laying on its side in the dirt . Of course, this does mean that I have to crack the throttle open slightly when downshifting to keep some lubrication going in!

        Consequently I have to try and hold the throttle slightly open when sitting in the mock-grid to try and maintain a steady rpm about 1,500 to 2,000 to warm up the motor, not always easy when surrounded by others constantly blipping their throttles. I have found from past experience that it is important to get the motor up to working temperature before going on the track or a cold seizure is most likely. I would rather have the motor too hot than not warm enough as it soon reaches normal temperature once moving. That is why I am usually first up to the mock-grid when my race is called .

        Stan

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        • #5
          Thanks Stan - understood. When all this bug stuff is over, see you in Lymington some time. Cheers Rene

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