Mikuni VM on a 750?

jko_78

jko_78

Full member
Location
The ever windy Northwest of Europe
In between I've been reading a lot on new carbs. My VHB's are old and rattly, and though they occasionally come up second hand I have no idea how good they are (sellers often are a bit optimistic about their wares I've noticed :D ), and if they are known-good (i.e. rebuilt by a renowned specialist) they are quite expensive.

A lot of threads here are about 3cyl conversions, but somewhere I read that Mikuni VMs are a possibility. Is there a conversion out there, does anyone run them, or does anyone have some pointers if they actually fit and such? Since my bike is far from original anyway I want something that works and originality is not really required.

Any pointers, tips, links?
 
Paul Marx said:
A friend fitted some to his GT some years ago.
So it can be done.
Are your VHBs really cooked? They're near eternal. Slides are easily obtainable.
Paul
Click to expand...
Where please, Paul? Dellorto outlets haven't offered them for years.

True, VHBs are almost indestructible and infinitely rebuildable. The slides wobbled around from new (I managed to obtain NOS items and was disappointed by the slide fit), a few witness marks do not detract from functionality.

piet
 
sfcpiet said:
Where please, Paul? Dellorto outlets haven't offered them for years.

True, VHBs are almost indestructible and infinitely rebuildable. The slides wobbled around from new (I managed to obtain NOS items and was disappointed by the slide fit), a few witness marks do not detract from functionality.

piet
Click to expand...
Which cut aways are you looking for?
Eurocarb have plenty of 50.
Andy Wagner lists them.
Paul
 
I have seen Mikuni VM on SF (and British twins), the only issue being that they never seem to have the choke on one side accessible. You won't find any kit, it will be fitting up yourself and working out all the jetting, could end up a lot of time and money compared to prerservering with the Dellorto. Alternative could be to fit PHF 32, probably easier to jet and get bits for than Mikuni.
 
Thanks for all the replies -I'd hoped ideally there would be a kit & some basic settings out there, as I don't trust myself to setup jetting, needles and what not, I can work with my hands but am not experienced enough for this kind of stuff. If they are really that good generally speaking it's not surprising I guess there isn't any. Good tip on the chokes too, hadn't thought about that.

I'll take a better look & take some photo's of the VHBs, my father took them apart before I got the bike and told me the bodies, slides and needle seat were worn. Since they are not too dissimilar (other than being square as opposed to round) to my BMWs, I'll have a look myself.
When all the new job stuff is more or less done I'll have a look and take some photo's. Any basic measurements I could take?

If the bodies are worn, can those be reworked, or are they fit for the bin only? They have done ~180.000km and were already used before they were fitted, so they haven't just been sitting looking pretty in the past ;)
 
There's a nice SF on UK eBay at the moment near me (see link) fitted with Mik VMs. My brother knows one of the vendor's friends in the motorcycle profession who vouches for it, says it runs well.
Mikuni jets and slides aren't cheap and given the number of variations it can take a fair bit of experimentation to get it right, took me ages on my Triumph 750 Bonneville and it's quite a common mod for those! Great carbs though, no slide wear (or rattles) in thousands of miles of use on a british twin and rubber mounted which is good for temperature and vibration isolation.
The choke is always on the left hand side which doesn't matter, it's just a cable operated plunger like the dellortos. With the hose clip loosened they're off in a minute if you need to access it.

I would imagine you'd realise a small performance gain versus the VHBs, about the same as PHFs in flow terms. Guzzis of the same period usually benefit from a VHB to PHF swap for example, sure there's more expert opinion on here than me on that conversion, but VMs do flow slightly better than Amal mk1 s for example. Might not be important to you.

ebay.us

laverda 750 sf | eBay UK

Short video of bike running,, done before I cleaned it. Paintwork not Brilliant, and would benefit from re-paint. Recent starter clutch re-furb by Motalia.
ebay.us

Hope that helps

Dave
 
wavey_davey said:
There's a nice SF on UK eBay at the moment near me (see link) fitted with Mik VMs. My brother knows one of the vendor's friends in the motorcycle profession who vouches for it, says it runs well.
Mikuni jets and slides aren't cheap and given the number of variations it can take a fair bit of experimentation to get it right, took me ages on my Triumph 750 Bonneville and it's quite a common mod for those! Great carbs though, no slide wear (or rattles) in thousands of miles of use on a british twin and rubber mounted which is good for temperature and vibration isolation.
The choke is always on the left hand side which doesn't matter, it's just a cable operated plunger like the dellortos. With the hose clip loosened they're off in a minute if you need to access it.

I would imagine you'd realise a small performance gain versus the VHBs, about the same as PHFs in flow terms. Guzzis of the same period usually benefit from a VHB to PHF swap for example, sure there's more expert opinion on here than me on that conversion, but VMs do flow slightly better than Amal mk1 s for example. Might not be important to you.

ebay.us

laverda 750 sf | eBay UK

Short video of bike running,, done before I cleaned it. Paintwork not Brilliant, and would benefit from re-paint. Recent starter clutch re-furb by Motalia.
ebay.us

Hope that helps

Dave
Click to expand...
Looking at the pics on EBay it looks like the cylinder head nut by the spark plugs is missing and no sign of the stud? Might be the picture but it’s leaking badly from there as well.
 
I doubt it's claimed to be professionally installed, also doubt it impacts the way the bike runs and am VERY certain it has fuck all to do with the question being asked by the original post.
 
wavey_davey said:
I doubt it's claimed to be professionally installed, also doubt it impacts the way the bike runs and am VERY certain it has fuck all to do with the question being asked by the original post.
Click to expand...
My point is, a carelessly chucked-in-the-tooltray ignition system that initially cost a small fortune reflects more than a bit on how well that bike has been assembled and maintained. Even though it has Mikuni VMs fitted, viewing the overall condition I'd seriously doubt the bike runs at full potential, despite a "professional" opinion. Describing such a tatty heap as "nice" is very distant from what I'd consider a "nice" bike.

Make what you want of it...

piet
 
before you buy different carbs and introduce more potential problems, get a Dell Orto rebuild kit and follow the directions. Ducati Paddy in UK , DAM Classic Racing in OZ, and Bevel Heaven in California are good sources, along w the usual suppliers.
 
wavey_davey said:
There's a nice SF on UK eBay at the moment

ebay.us

laverda 750 sf | eBay UK

Short video of bike running,, done before I cleaned it. Paintwork not Brilliant, and would benefit from re-paint. Recent starter clutch re-furb by Motalia.
ebay.us
Click to expand...
That’s a 1972 SF.
One could stabilise the DMC box with a dead rat or squirrel. 😉 Joking aside, at least the seller shows this messy situation in a photo, not sure if that was done intentionally though.

Marnix
 
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