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[Blown265]

I currently use a VM34 on mine, and it does everything perfectly.
Purchased from our hosts, it ran well as delivered. Once setup up to suit the bike, it's now perfect- crisp, clean, powerful.
Size will depend on the modifications to your 612, but you'd be in the ballpark with a VM32 or VM34.
Regards
Paul.

[Presto]

Hitchcocks 612 champion winning scrambler produced over 50bhp at the back wheel on a 36mm Mk 1 Concentric! I don’t buy into this idea that the Mk 1 isn’t up to the job.
It all depends on correct setting-up – and the competence of the setter-up!

[mauri]

have are host mikuni kit on my 612 for many years.



needed minimal set up.
and has been trouble free with the exeption of the rubber mouting flange.
which was prone to sheering, also due to the older series being shipped with a over the top airfilter.(size and weight)
problem has been solfed with a aluminium flange and separate rubber connection and correct airfilter.

you can even add kit 90195, but you have to change the plunger as it is initially for a Mikcarb.
as i did on mine, due to the fact that the older series did not come with a lever as of now.
it work a treat.

[stinkwheel]

It runs fine with the Amal once you're out on it so I don't think it's a setup issue. The issues I have are with the Amal are mainly to do with starting drill, cold running and getting it to prime.

Yes it starts but you need the choke in just the right position and to have tickled it just the right amount. It can't really be left to idle itself until warmed up, the choke is too fussy. I also find they will refuse to fill with fuel if parked with the float bowl full then not touched for a couple of weeks, not even if you tickle them.

I've had the same issues with two different Amals on two different bullets. I'm also fed up of regularly messing about with the choke lever when it turns itself on through vibration and having to ride about with a screwdriver in my pocket in case it does so

There is also a tendancy to have an iffy transition between main jet and slow running meaning they tend to conk out if you come to a sudden stop from flat out or have been idling for a while and want to set off.

I fitted one to my 350 in the belief it was an upgrade and now realise nothing could have been further from the truth. I have other mates with "hot" Brit bikes and they also landed up on Mikunis.

I'm totally fed up of getting my gear on to go for a ride then having to take it all off again to disconnect fuel lines and tinker with the carb. The only thing I should have to touch on a carb from one year to the next is the choke lever.

@Mauri, good to hear that. I wasn't sure if the baseline for the 500 setup was going to be anywhere close enough to the 612.

@Blown 265, I didn't know our hosts did a 34mm, more food for thought.

I do hear good things about the TM (flastslide) models though. Seems to be the go-to carb in the USA.

[Presto]

Forgive me – no offense intended – but I have to comment on all this – because it’s unreasonable to blame all this on the Mk 1.

You need the choke in just the right position and to have tickled it just the right amount.
That is setup.

Can’t idle itself until warmed up.
That is setup.

I also find they will refuse to fill with fuel if parked with the float bowl full then not touched for a couple of weeks, not even if you tickle them.
That is malfunction – not a design fault but a maintenance fault.

I'm also fed up of regularly messing about with the choke lever when it turns itself on through vibration and having to ride about with a screwdriver in my pocket in case it does so
That’s malfunction – maintenance

They tend to conk out if you come to a sudden stop from flat out or have been idling for a while and want to set off.
That’s setup – and riding style – blip the throttle on big single when coming to a halt.

I'm totally fed up of getting my gear on to go for a ride then having to take it all off again to disconnect fuel lines and tinker with the carb. The only thing I should have to touch on a carb from one year to the next is the choke lever.
All this is setup.

How can it be reasonable to attribute all this to 'poor design' or whatever when there are 10,000 of these Mk 1's fitted and used without any of these 'issues'?

[windmill john]

Hi Presto,

Pop round will you and get my Amal monobloc to start first second or third kick when cold, there's a good chap, many thanks

I think whinging is the wrong word. We'd all buy new bikes if we didn't like to fiddle.

I've just picked up a Mk1 to test, but need to change the slide. I could continue kicking as is, but agree with most of Stinkwheel's woes.

I'm new to RE, under a year, but have spent a lot of time fiddling with the carb. Maybe it's the nature of the beast and we should ask for a report from the 10,000 happy campers.

I normally get carb issues resolved, but have to say, nothing was as bad as the Keihin CVs on my old Honda CB500T; don't start Paul

John

[Presto]

John I’m sure you’re able to get that starting problem sorted without any interference from me. But I wasn’t defending the Monobloc but the undervalued – by some – Concentric Mk1.

I meant to write 10,000s – over the last 60 odd years I’m sure that there are far more than 10,000 happy users of this probably most used of all motorcycle carburettors.

[Wheaters]

I’ll say it again, but the Wassell concentric (Amal copy) on my 350 has never caused a bit of trouble, after the very troublesome VM24 caused me lots of it.

Having set up the Wassell I discarded the choke mechanism (having ordered a cable and lever) because the bike simply doesn’t need it and I saw no point in over-complicating the issue. All I’ve done to it since is to fit a 170 main jet, rather than the 160 that the manufacturer supplied, simply because I could tell from the plug colour and performance that it was slightly weak at the top end.

It starts first or second kick from cold (provided I use my normal procedure) and having run it gently for thirty seconds or so, which I do on all my vehicles to allow the oil to circulate, it rides perfectly. I don’t expect it to idle on the throttle stop until it’s warmed up, so I use a small amount of throttle if I have to stop.

[Presto]

Exactly right Wheaters!
If an engine idles well when cold the setup is wrong. Idle should be set for a warm engine. Until then idle should be - and will need to be - faster than a 'correct' idle speed.

[stinkwheel]

Frankly. I have wasted enough of my life and motorcycling time "maintaining" and "setting up" Amals.

The "malfucnctions" which require "maintainance" are exactly why I want to sack the damned thing off. They are inherant to the design. A choke that is on in the at rest position, a choke lever the unscrews itself, a float bowl that fills from the bottom and a needle valve that has to be lifted up out of its seat by the float. The idle circuit design is shonky as hell, you just have to look at it to see that, it's like they made a carburettor then suddenly realised they'd forgotten a slow running circuit and had to squeeze one in somewhere.

Anyway. This is all a digression, the amal IS being taken off and replaced with a mikuni carburettor because I am now totally and utterly fed up to the back teeth with it. I'm just looking for a baseline setup for one.