Mikuni on a Monza

[cooperplace]

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

That is the manifold that Sudco sold me. I cannot get it to work, despite its hefty price. With the 50mm bolt spacing, that manifold is squished into an oval when its installed. Yes, I can push the VM26 into it and tighten the hose clamp, but it doesn't seal, which is why it's backfiring. I've ground away as much of the wall thickness of the manifold as I dare, and still it won't allow the carb in to do a proper seal.

[cooperplace]

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.

stock ducati manifold? There isn't one: on my 250 the Dellorto carb bolts directly onto the head. No manifold.

[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

Hi Chuck,

can you please advise where you got that bit of hose, the rubber thing that attaches the carb to the manifold?

thanks

Peter

[amartina75]

The stock mikuni manifold uses 60mm bolt spacing, I believe. Most old Brit bikes use 2" spacing. The ducati is 52mm, which is 2.047". You could try a manifold made for converting a Brit bike to mikuni carb. They are available on eBay.
Possibly oval out the holes slightly so it fits or you could install 8mm to 6mm studs.
360285389975 eBay item # in UK

image.jpg

You could also try to find a local shop to make you one, if you make a pattern for them it would be cheaper.
Try to find a motorcycle enthusiast, they will probable give you a better deal.

[Nick]

Some of the Ducs do use spigot manifolds, find one and use the rubber hose mentioned above.

Or, save the Mikuni for your next Duc, and bolt on an Amal concentric (they bolt right on, just don't over-tighten!) An Amal from a 500 Triumph Daytona should work fine with the Triumph jetting.)

Or, have someone help you make you a manifold so you can use the Mikuni. You can cut the base plate out of aluminum using a hack saw, trim it up with a file or belt sander, drill a big hole in the middle and a couple more for the studs, weld on a piece of aluminum tube at the desired angle, then file to finish. Easy, peasy, oder? Then imagine how proud you will feel knowing that you made your own part for your own bike!

As a last resort, you can always make do with the stock carbie (horrors!).

[cooperplace]

That british bike manifold looks good. On the Ebay site, it says "best attached with Allen bolts". Yes, I had already worked this out. But that means removing the existing studs. I tried to do this by locking two nuts together and succeeded in stripping _some_ of the thread. I still have enough thread to attach a manifold, so maybe I'll order the aluminium one from Guzzino:

http://guzzino.stores.yahoo.net/duinma250350.html

because continuing to try to get the studs out will be my worst nightmare: stripped thread, stud stuck in place.

[amartina75]

i wouldn't try to remove the studs unless i were going to replace them or use stepped studs to make them 6mm. the ones on guzzino are reproduction of the original, they are zinc or cad plated steel.
pretty expensive IMO. I'd recomend trying to find a used original one on ebay.

[Rick]

You should try to replace the studs if the threads are stripped, the best method I've found- especially if the double nut failed, is to put a nut on the stud just slightly above the end of the stud and weld the inside of the nut to the stud. The welding heat will slightly expand the stud and possibly breaks some of the corrosive bond, but it will also make the stud more brittle just past the weld, so be careful not to snap the stud off. I'd use an impact gun on the welded nut in very short bursts- drop the trigger as soon as you pull it- if the stud breaks off below the surface of the head you've got a big problem.
I like to see people fix things rather than do a halfway repair- someday you'll probably sell the bike and the new owner shouldn't have to fix a 'might work for a while' repair.
Rick

[amartina75]

Yes if they are damaged I'd replace them, I'm not sure why you were trying to take them out though. Was it because they recommended using Allen head bolts? That was surely just a recommendation, and also for the intended application of Amal to mikuni on a Brit bike, also with the standard 2" hole spacing. That's really not what you are doing. If you don't feel comfortable taking the studs out you could always take the head to a local machine shop. They shouldn't be too rough on you for just replacing a couple studs. And if it turns out you need a helicoil put it they can do that also.
Hopefully you might have some friends with tools, it's nice to know people with welders and lathes and mills. They make everything easier. Good luck

[double diamond]

The double locknut technique will usually work to remove the studs but you may want to try some extra measures. Heat the flange with a propane torch or heat the entire head in an over set to 250 degrees. Have a can of computer keyboard compressed air at hand (often called “keyboard duster”). The keyboard duster is actually liquid air and at that pressure, the liquid air is really cold. Use precautionary measures (goggles, gloves). Invert the can so liquid air will be discharged and spray the heated stud. This will make the stud contract ever so slightly and make it easier to remove. Be sure to turn the lower locknut (the first one installed on the stud) to loosen the stud. This technique has worked for me on some very difficult studs and press fits that required heating to diassemble. The reason for installing allen bolts is that with these manifolds there may not be enough room to get a socket or wrench on the nut that holds it in place because the mounting holes are so close to the spigot the carb fits into.