Mikuni on a Monza

[Chuck]

I finally gave up trying to get the UBF24BS Dellorto to work on my '66 Monza and am now using a Mikuni VM26 carburetor. The bike start cold with one or two tries and also starts hot. The motor idles and has power throughout the rpm range and is a pleasure to ride. I have had lots of classic British bikes and was always able to get the Amals to work but the Mikuni is better.

Chuck

[JimF]

I must admit, the Mikuni on my 250 works very well after I jetted it correctly - I can fine tune it more than I can the DellOrto SSI29 on my other 250.

The Mikuni wears the scrambler circular air filter can that says "DellOrto" so it looks the part on the Ducati.

Jim

[ecurbruce]

Jim,
Sorry for resurrecting this thread after so long, it just seems a good place to ask...
Are you still satisfied with the performance of the mikuni carburator on your 250? What jets did you end up with? Do you remember, or have it written down somewhere?
I ask because I'm ordering a new VM26, and thinking your jetting must be the best place to start... if it works well.
I read back through several of your mikuni posts, and could not find it, but it seems you ended up with a 120 main jet?

Thanks,
Bruce

[JimF]

I am very happy with the Mikuni. I did sort it by addressing engine response, performance and spark plug color throughout varying throttle openings (carb circuits). I bought many jets from Sudco, as they gave me a starting point but my engine needed subtle variations.


I will look for the original "Sudco" recommendations and my changes to that.

Jim

[JimF]

I talked to Chad @ Sudco (310-637-8330.) I don't know if he still works there.

Here's Sudco's recommendation (based on 40 years experience) for a Ducati 250 running a VM26:

140 main
30 pilot
182-02 needle jet
5DP7 needle
2.5 slide
0.5 air jet

I did wind up with a 120 main. If I deviated elsewhere I don't recall but I will try to find out short of taking the carb apart.

This is exactly the kind of stuff I should write down when I am doing it, but my MO is to go to fast and not pay attention to the details.

Jim

[ecurbruce]

Jim,
Thanks for the reply, and specs. That's about the way I remembered it, now that I see it, just couldn't find it. Also good to know that you're solid on the results, gives me a good baseline.
Please don't take your carb apart for this, I'll get close enough without going to that extreme (you probably weren't going to anyway).
My vintage OEM mikuni 26 has a non- standard 134 size needle jet,that's no longer available, and non-servicable air jet,,, so I've hit a brick wall on being able to tune it further. And I didn't get where I needed to be with it. It's getting replaced.

Thanks again for the info,
Bruce

[cooperplace]

I finally gave up trying to get the UBF24BS Dellorto to work on my '66 Monza and am now using a Mikuni VM26 carburetor. The bike start cold with one or two tries and also starts hot. The motor idles and has power throughout the rpm range and is a pleasure to ride. I have had lots of classic British bikes and was always able to get the Amals to work but the Mikuni is better.

Chuck

can I ask where you got the inlet manifold shown in the photo in the original post? That would fix my problem, I think. I would love to get my hands on something like that.

[ecurbruce]

Sudco sells a manifold that can be made to fit, page 225 in their online digital catalog
Syd Tunstall at Syd's Cycles in St. Petersburg FL custom made mine for a hefty price.

Bruce

[cooperplace]

Thank you. I will look at the Sudco catalog. I was worried that it might involve a big $$$ custom job.....

[Nick]

I was in the same situation when putting a Mikuni on my 350 Sebring. Thought I'd use the trick Sudco manifold until I saw the price! What a joke. Went down to the hardware store, got a piece of PVC pipe with the same OD as the Mikuni OD. Then, if you have access to a lathe or know someone who has one, bore out the PVC so that it slides snugly over the stock Ducati manifold, then blend the other end to match the ID (in your case 26mm) of the Mikuni. Radiator hose and hose clamps and you're good to go, all for about $4.00.

And yes, the Mikuni is one of the best things you can do for your Duc, especially if you actually intend to ride it regularly.

Rode my Sebring to work today and it was, as usual, a pleasure.