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Single Carburettor

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I am sure that this is a topic that has been discussed many times before but here goes.  I am planning to fit a single Mikuni carb to my 850 engine which is currently being rebuilt by Norman White.  There does seem to be 2 schools of thought on which size carb to fit; the VM34 or VM36.  Has anyone got experience of using both or either and which is the better?  I am looking for easy starting, good tick over and low to mid range pick up without hesitation.  I am not looking for out and out top end performance as I am far to old for that :-)

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Hi Graham,

Smaller carburettors are a lot easier to calibrate for good idle and smooth progression from idle as the gas speed is greater. Personally, I would expect there to be an undetectable power difference (caveat - both carbs being properly jetted) between the two carbs until the engine was north of 5000rpm.

When the Ducati 900 was a current model (late '70's) I got to ride both a 900SS and a Darmah on the same day.

The Darmah was by a long way the nicest of the 2 to ride - not talking ergonomics or comfort - as it 'drove' so much more easily at normal speeds and especially around town. The Darmah had 32mm carbs, the SS 40mm. 

Hope this helps your decision,

George

 

 

I fitted a 34mm single Mikuni to my Mk3 around 20 years ago. I have done around 80,000 miles with the carb needing little attention. I was advised at the time that a 36mm carb would increase the petrol consumption but would make little or no difference to the useable power other than at the top end in 4th gear.

 

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Hi Tim,

Was that attention late August 2017 on Olivers Mount, Scarborough and fixed by the Great Late Mark McLennon? I seem to remember the carb coming loose and you had to manually richen the mixture to keep going. I have the photo. Treasured memories.

For me, my Mk 3 Commando runs very well on a single 32mm Mk 1 Amal.  (68 mpg) E0 petrol.

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I run a VM 34 with the 2-1 manifold cleaned up to blend with the ports and the largest K&N filter that would fit in. Running with a PW 3 cam, good for road speeds but probably looses out at top speed on a track. Pulls strongly low and mid range and uphill.

 



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