Author Topic: Dragonfly carb  (Read 1904 times)

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Offline davrhos

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Dragonfly carb
« on: 05 Feb 2012 at 12:07 »
Long standing member and owner, but new to forum, so Hi everybody.
  After 40 years ownership, have decided to replace carb on my D/fly, however
only new alternative is 15/16", whereas original is 13/16".   Has anyone had experience of running the bikes on the oversize carb?
  Davros. Mem 344.

Offline eddie

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Re: Dragonfly carb
« Reply #1 on: 05 Feb 2012 at 14:19 »
Hi Dave,
             Physically, it shouldn't be a problem fitting a 15/16" bore Monobloc carb on a Dragonfly as the 375 and 376 were - overall - dimensionally much the same - just the choke size and slide was smaller. Also, the bore of the inlet tract (in the bellhousing) is only marginally smaller than the 15/16" of the new carb, so there shouldn't be any appreciable step down into the manifold. The only other thing to check is whether your twistgrip has enough travel to enable you to get full throttle with the bigger carb. A bigger carb of course means slower air speed through it, so correct tuning may need to be a little more precise to obtain clean pickup in the lower rev range. Also bear in mind that the 1/8" increase in bore will actually increase the cross sectional area by about a third, so you will need to increase the main jet by about the same amount - say a 180 or 190. Obviously, you will have to experiment with the throttle cutaway, but I would suggest that you start with a No.3 slide as the modern unleaded fuel seems to cause our old motors to run a little on the weak side. Also, be wary of running on "super" unleaded petrol as this has a higher viscosity rating and tends to run even weaker in engines with carburettors - it doesn't seem to affect fuel injected engines as a specific amount is pumped in on each induction stroke.
        Good luck with the conversion.
                                  Regards,
                                                  Eddie.

Offline davrhos

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Re: Dragonfly carb
« Reply #2 on: 06 Feb 2012 at 20:30 »
Thanks Eddie, will give it a try.
Regards, dave