Mikuni VM24

[George]

for what it is worth according to Ian Fallon's book Overhead Camshaft Singles, 350 scramblers from 1971 to 1972 engine numbers were from 11051 to 22500 and had a Dellorto VHB29A carb

[Mark3Cam]

It wasn't obvious from the post that this was a W/C. It's obviously from these pictures it's W/C probably circa 1973 and a 24mm carb is too small relative to the port size. A strange choice of carb for the previous owner.

The port has obviously been modified in some way if it is close to 32mm. The largest standard port on a spring valve W/C single is 29mm. As you say a 30mm carb should work OK.

Regards Nigel

Thanks Nigel! It is starting to add up now. If the frame is from the late 60’s(likely a 68) then the bike would have originally come with a narrow case engine? Perhaps the 24mm carb was a swap from the original engine when the previous owner switched to the newer engine?
She was rough when I got her but starting to come together now

C4E40B49-263D-4D0D-86AA-D92193A58E34.jpeg

5FDA90CA-1169-4C11-BF3F-80E625932A3A.jpeg

[graeme]

You have a wide case frame.
Narrow case frames are different.
Don’t put too much faith in Ducati numbers matching a certain year build.

Graeme

[Mark3Cam]

It really is a crap shoot with Ducati of the singles time era! I will probably never know what this bike was originally! Oh well still love it

[Dan C]

Bit late to the party here.
Yep engine numbers can be very deceptive. My 350 has been re-stamped as a 250. I only know this because the previous owner told me he'd done it, the reason being that back in the day anything 250 and under was a lot cheaper to register in NSW. If I didn't know that, I would have assumed someone had put a 350 head and barrel on a 250.....
Anyway back to the carb and the appropriate jetting. Since fitting the VM30 carb I haven't ridden the bike a lot, I still need to sort an oil leak and it's cosmetics are now getting a well overdue upgrade, but the carb (with the jetting mentioned earlier in this post) seems fine for all round useability except for just off idle where its still a bit rich so I need to try a 25 pilot. Hope that helps.

Cheers Dan

[ducwiz]

If I didn't know that, I would have assumed someone had put a 350 head and barrel on a 250.....

This is not as easy as it looks or sounds. The (cast iron) cylinder liner does not fit into the opening of the 250 case, hence this has to be machined to the approptiate inner diameter. The 350 primary gear set has a different ratio, has to be changed too. And of course you need not only the cylinder head but all the upper bevel parts including the guard tube; shaft and tube are longer than the 250 parts.

Hans

[Mark3Cam]

Here’s a pic of the VM30 dry fitted to the engine
Did a top end oil flow test that looked positive too and also getting the regulator all figured out as well…progress boys!

A9D0DB64-573C-4415-AC40-3534B7575B63.jpeg