Issues with my Mikuni VM34

robs ss said:

It may be that someone here (according to Freudian psychosexual theory) may have excess libido stuck in their anal stage (1-3 years old)

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Really? And who would that be? Freud was discredited years ago. He had his own problems. And your point is?

Fullauto said:

Really? And who would that be? Freud was discredited years ago. He had his own problems. And your point is?

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My point is, much to my embarrassment, that I actually must have listened to some of those boring psychology elective lectures in 1977 - whoda thunk?

Fullauto said:

Really? And who would that be? Freud was discredited years ago. He had his own problems. And your point is?

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....or another way of saying it is - it really is a bit puerile to "call denigrating names" on someone else's choice of carburettor simply because you choose not to use them.
I'm sure forum members expect a bit better than that.

Just to get the thread back on track as far as single carburetors (I would still use a TM40 with a fabricated manifold) , has anyone used one of Phoenix SU kits out of the UK ?

No carb type is completely without issues.
I get by Ok with Mikunis on two bikes but they have not been as trouble free as the Premieres.
The biggest issue has been sticking floats on the VMs. These were new units that had problems from the get go.
Do an internet search and it's obvious that many VMs have this problem
Another minor issue is the very heavy spring tension. Not a problem with a single but makes for a very heavy throttle on twin carbs. The twin Amals give a light, easily modulated throttle.
I've tried lighter than stock springs in the Mikunis, but that did not work.

Starting is also better with the Amal equipped bikes.
The tickler seems to facilitate cold starting better than the enricheners of the Mikunis.
Finally, cosmetics are a minor concern but definitely part of the package.
Mikunis are a bit of a homely apparatus.
It's as though the designers said " no one will ever see this, it just has to work" whereas all Amal carbs, up to but not including the MK2 Concentric, are designed with an eye to appearance. They are nicely shaped and look right on there.

worntorn said:

No carb type is completely without issues.
I get by Ok with Mikunis on two bikes but they have not been as trouble free as the Premieres.
The biggest issue has been sticking floats on the VMs. These were new units that had problems from the get go.
Do an internet search and it's obvious that many VMs have this problem
Another minor issue is the very heavy spring tension. Not a problem with a single but makes for a very heavy throttle on twin carbs. The twin Amals give a light, easily modulated throttle.
I've tried lighter than stock springs in the Mikunis, but that did not work.

Starting is also better with the Amal equipped bikes.
The tickler seems to facilitate cold starting better than the enricheners of the Mikunis.
Finally, cosmetics are a minor concern but definitely part of the package.
Mikunis are a bit of a homely apparatus.
It's as though the designers said " no one will ever see this, it just has to work" whereas all Amal carbs, up to but not including the MK2 Concentric, are designed with an eye to appearance. They are nicely shaped and look right on there.

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So, it really comes down to "it looks better".

robs ss said:

....or another way of saying it is - it really is a bit puerile to "call denigrating names" on someone else's choice of carburettor simply because you choose not to use them.
I'm sure forum members expect a bit better than that.

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Hahahahahaha! Spoken like a true believer in his own psychology.

Fullauto said:

So, it really comes down to "it looks better".

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How do you get to that from the issues I detailed?
Cosmetics were mentioned at the end and listed as less important than function.
I guess you read the last sentence but skipped the rest.

Glen

Funnily enough, I have Mikunis, Keihins, Amal MK11s and Amal Premiers, fitted to my ‘stable’ so am able to compare them all easily.

The biggest challenge Japanese carbs give people using them on bikes they were never intended for is setting them up. Many folk struggle with Amal’s and Japanese carbs are many times more difficult to get right than Amal’s. Luckily for us, there are specialist suppliers out there and a whole internet community of people who have already done it, so buying a kit with good base settings is easy, and fine tuning with the help of the community isn’t so difficult any more. The really serious can do what Ken did and fit a gas analyser to their bike, but not many folk do this.

An issue I’ve had with Mikunis and Keihin carbs is their sensitivity to dirt. I’ve had them flooding out of the overflow pipe and, long story short, it’s been down to dirt particles so small I could hardly see them. Perhaps it’s not a ‘fault’ as such, it’s actually a symptom of the greater precision of the Japanese instruments and more of a calibration issue of the owners more used to Amal’s, which will run happily in situations where the Japanese instruments will not. Fitting good filters cures it of course.

Actually, the Amal’s work very well indeed, they start well, run well, tick over well, etc.
The MK11s were jetted incorrectly from Amal, not by error as such, but due to the fact that the Triumph manual and therefore the Amal, upon which they are based, are both wrong!
The Premiers came with pilot jets that turned out to be too small, this was a common issue which I believe Amal have now rectified.
Neither pair of Amal’s came with any swarf or assembly errors, but due to the reports of this, I did strip and inspect carefully.

So, overall, I’m happy with them all. The Japanese carbs are fitted to rather special / tuned engines, the Keihins have accelerator pumps which work very well, and, although I’ve never tried Amals in these applications, I cannot imagine them matching the performance of the Japanese carbs. And anyway, new Amal’s are not available in these sizes. The Amal’s I have are fitted to fairly standard bikes, and as they work so well, I see zero advantage in swapping these for Japanese instruments.

So once again it’s bad news for those looking for a fight cos IMHO it’s all down to different horses for different courses and personal preference.

Personally I have 3 28mm VMs on my trident I'd never go back to Amals
The only issue I have with these is constant flooding despite fitting viton tipped float needless and I have to glue the cables into the splitter box to keep them in balance and the throttle is heavy but the bike is so much better with these than Amals that I can live with it
I had a 34 VM and I've had a 36 VM and a 32 CV mikuni as well as a single 32 mm concentric on my commando but the single TM 40 is a league away from all of these
The issue I have had with the single VM is mainly flooding and with the 36 VM the slide would often hang up the only way I managed to stop this was by fitting an Amal spring inside the mikuni one
But for me the bike was just too gutless
I presently have twin Amals on my commando I fitted these because the TM could be difficult to start when I only had a Kickstarter and knee surgery, the Amals are a one kick start for me
And they carburate perfectly so they are staying on for now
Wild horses would not make me refit a single VM to my Norton and similarly I would never go back to Amals on the trident
So I guess I have a foot in both camps?

worntorn said:

How do you get to that from the issues I detailed?
Cosmetics were mentioned at the end and listed as less important than function.
I guess you read the last sentence but skipped the rest.

Glen

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Well, you read into it what you want. You said it, not me.

baz said:

Personally I have 3 28mm VMs on my trident I'd never go back to Amals
The only issue I have with these is constant flooding despite fitting viton tipped float needless and I have to glue the cables into the splitter box to keep them in balance and the throttle is heavy but the bike is so much better with these than Amals that I can live with it
I had a 34 VM and I've had a 36 VM and a 32 CV mikuni as well as a single 32 mm concentric on my commando but the single TM 40 is a league away from all of these
The issue I have had with the single VM is mainly flooding and with the 36 VM the slide would often hang up the only way I managed to stop this was by fitting an Amal spring inside the mikuni one
But for me the bike was just too gutless
I presently have twin Amals on my commando I fitted these because the TM could be difficult to start when I only had a Kickstarter and knee surgery, the Amals are a one kick start for me
And they carburate perfectly so they are staying on for now
Wild horses would not make me refit a single VM to my Norton and similarly I would never go back to Amals on the trident
So I guess I have a foot in both camps?

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Well, remarkably fair of you Nigel. Actually, I was never looking for a fight, I just wished to point out the ridiculousness of some people's position on this. Even though you never experienced swarf, different jets etc, Plenty of people have. It should'nt be too hard to get right after 50 odd years.

baz said:

Personally I have 3 28mm VMs on my trident I'd never go back to Amals
The only issue I have with these is constant flooding despite fitting viton tipped float needless and I have to glue the cables into the splitter box to keep them in balance and the throttle is heavy but the bike is so much better with these than Amals that I can live with it
I had a 34 VM and I've had a 36 VM and a 32 CV mikuni as well as a single 32 mm concentric on my commando but the single TM 40 is a league away from all of these
The issue I have had with the single VM is mainly flooding and with the 36 VM the slide would often hang up the only way I managed to stop this was by fitting an Amal spring inside the mikuni one
But for me the bike was just too gutless
I presently have twin Amals on my commando I fitted these because the TM could be difficult to start when I only had a Kickstarter and knee surgery, the Amals are a one kick start for me
And they carburate perfectly so they are staying on for now
Wild horses would not make me refit a single VM to my Norton and similarly I would never go back to Amals on the trident
So I guess I have a foot in both camps?

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The flooding could be very fine dirt, at least it was with me, ie finer than the gauze in many filters. Sintered or paper are best in my experience.

Fullauto said:

Well, remarkably fair of you Nigel. Actually, I was never looking for a fight, I just wished to point out the ridiculousness of some people's position on this. Even though you never experienced swarf, different jets etc, Plenty of people have. It should'nt be too hard to get right after 50 odd years.

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Think you answered the wrong person

If you never go over 90 mph then the mikuni CV 32mm really would take some beating
But the TM 40 will give much more midrange than a VM 34 or 36 but with the added bonus of the top end of twin Amals

I have an almost new phoenix SU setup on my shelf
If I ever get around to fitting it I'll post my opinion on here if people aren't too sick of same old same old
Cheers

It’s revs Baz... not speed... more correct to say “if you never go above x revs” (but in any gear).

I don’t spend too much time above 90mph unless I’m on private roads (!).

But I like access to the full rev range in the lower gears in order to get my fix.

Interesting you mention the SU. I rode a trick 650 Triumph once that was fitted with an SU and it was a real flyer ! There were no Commando style space issues though, and it was on a long, shallow Y shaped fabricated manifold.

Fast Eddie said:

It’s revs Baz... not speed... more correct to say “if you never go above x revs” (but in any gear).

I don’t spend too much time above 90mph unless I’m on private roads (!).

But I like access to the full rev range in the lower gears in order to get my fix.

Interesting you mention the SU. I rode a trick 650 Triumph once that was fitted with an SU and it was a real flyer ! There were no Commando style space issues though, and it was on a long, shallow Y shaped fabricated manifold.

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Yep I realize it's about the revs ,I was just generalising
As a sidenote when I was tuning the single TM 40 I had a flatspot at 6500 rpm but if you hang on it got through it at around 7000rpm and it was picking up at 7500 rpm this is the highest I have ever revved my commando (a 750) I keep it under 7000 rpm normally

Fast Eddie said:

It’s revs Baz... not speed... more correct to say “if you never go above x revs” (but in any gear).

I don’t spend too much time above 90mph unless I’m on private roads (!).

But I like access to the full rev range in the lower gears in order to get my fix.

Interesting you mention the SU. I rode a trick 650 Triumph once that was fitted with an SU and it was a real flyer ! There were no Commando style space issues though, and it was on a long, shallow Y shaped fabricated manifold.

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Nope.
The engine will rev 7000 in first gear with a tiny carb.
Ask that in fourth, it won’t.
It’s the difference between “free revving”, and making an engine’s “full power”.

baz said:

Think you answered the wrong person

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Sorry Baz. You are correct.