Misc: Ignition Need Advice, can't keep an idle (intermittently) approaching or at a stop with New Amal 276's

Gene Nehring

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VOC Member
Hi Eddy,

I am contemplating fitting a 28 or 30mm Mikuni to my Comet but have NO experience with setting them up. Are you able to share with me the configuration, jets selection etc?

Many Thanks,

Martyn
Martyn,

I have a vm28 set up for comet sitting on shelf. It was supplied by Mikuni set up for a comet with jets etc. I could also supply the right manifold. DM me and we can arrange a price and shipping to aus if you’re interested.

Best,

Gene.
 

BigEd

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VOC Member
VOC Forum Moderator
Hi Eddy,

I am contemplating fitting a 28 or 30mm Mikuni to my Comet but have NO experience with setting them up. Are you able to share with me the configuration, jets selection etc?

Many Thanks,

Martyn
Dear Martyn,
When I first built my 1948 Rapide from a pile of mostly worn parts I fitted two second-hand Amal Monobloc carburetors. (I was on a tight budget back then.) The bike ran quite well on these and once I'd got the bike registered and on the road (late 2008) I completed a few thousand miles. Although it started easily and ran well the slides would often stick if If went over half throttle. I tried a lot of "fettling" but never really got it sorted. This is not a condemnation of the Monoblocs, they were very second-hand but served the purpose of getting the bike up and running. Stuck open throttles can lead to interesting experiences that are probably best avoided! ;) I thought about having the Monoblocs sleeved but when I looked at how much this would cost it was as cheap to get two new Mikuni VM28 carburetors. Originality is not important to me so I've used the Mikuni carburetors for most of the 50,000 miles I have put on the clock.
The settings as supplied by Motocarb were:
Main Jet 190
Needle Jet P-6 (182)
Needle 5FL 14
Slide 2.5
Pilot Jet 30
Air Jet 2.0

That is what I used and suggest that these would be a good starting point that you could test and adjust to the engine configuration on your Comet. I put the needle in the middle slot and experimented from there. There are lots of different needle types for Mikuni carburetors but for a Rapide it doesn't seem critical. I reduced the main jet to a 160 but now that I am now running 8:1 pistons and a straight-through Armours silencer I will probably increase the main jet size once the Covid 19 restrictions allow us to get out on the road again to do some testing.

An observation on the Mikuni carburetors is that they seem to be very well made. The aluminium body casting is of good quality, possibly LM24. The slides feel quite weighty so are probably brass and they are chrome plated. There doesn't seem to be any significant wear.
I've no recent experience of recently made Amal carburetors but would think (hope) that the materials used now would be better than the built down to a price of the originals.
I did have a new Norton Commando in the early 70's that had two Concentric carburetors that worked OK. As a teenager, I had a BSA Gold Star with an Amal GP carburetor and my brother used Amal TT carburetors at times when we were vintage racing. The GP and TT types seemed well made with better materials.
 

stu spalding

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VOC Member
Hi Martyn, my VM28s came from Allens over 20 years ago with the following settings and I haven't adjusted them since.
Slide no 2
Main jet 160
Needle 5 F 21
Clip 2nd from top
Emulsion block 169 0-8
Pilot jet 30
The standard mounting rubbers are poor, as Ed suggests, radiator hose is much better, Cheers, Stu.
 

Martyn Goodwin

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Non-VOC Member
ps Martyn, sorry, my settings are for a twin. I should look before I leap, Cheers, Stu.
Stu,

I figure a single is just half a twin except it revs a bit harder. So I expect all the settings to be the same except the main that may need to be one or two sizes bigger.

Thanks for your help

Martyn
 

Peter Holmes

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VOC Member
According to "Richardson" Post War Comet and Shadow Carb Settings
Comet:- Main: 200, Slide: 29/3, Needle: 3, Needle Jet: Std
Shadow:- Main: 180, Slide: 29/4, Needle: 3, Needle Jet: Std
If those variations relate to other carbs like Mikuni etc. I have no idea.
I have a pair of VM28s waiting to be fitted, they were supplied and jetted by Steve at Motocarb I seem to remember, my bike runs so well on the original Type 29s I can't bring myself to upset the applecart, maybe one day, but the years are rolling by!
 

greg brillus

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VOC Member
There is a huge difference in the slide from a 3 to a 4 That just shows how much more fuel the single needs to be happy........I'm a big fan of the original carb's though some on here might disagree........apart from the odd drips of fuel, they are easy to setup, they last a long time, and they don't seem to block up in their low speed circuits like all the newer carby's do........Most concentrics, Mikuni's and the like tend to block up their pilot jets if left for 3 months or so. Well in our hot climate at any rate.......
 

greg brillus

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VOC Member
Absolutely Peter, they look great.......I can see why owners gave up on them if they were badly worn and too hard to keep in tune.......I use them on all the resto's that I do, but the cost of them has gone though the roof, so buying them now is a big question mark......The Shadow ones especially.......
 

Bill Thomas

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VOC Member
For every day running I am a big fan of Amal Mk2,
Made much better than Mk1, Maybe some slide problem, But I will put up with that.
The 30mm went straight on my Comet, Flash spec, And went and started well, Amal settings,
For 30mm.
 
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