Single Mikuni or Amal Mk II

i had a mk2 amal on my commando for a while . Please DONT bother it was rubbish .N o matter what i did with it flat spots everywhere .Best of all it would freeze up anywhere below 3 degrees centigrade . Then it would be very bad black exhaust smoke running rich as hell oh yes and the slide would freeze open TERROR ! That commando has a Mikuni on it now i have never looked back . My other commando has two Mk 1 concentrics on nice but the Mik needs less attention ,and the MK2 Amal ? it went in the bin i would not pass that rubbish on to anyone

need to find the post but fullauto of course has the best answer imho, in another thread..

After the experience high lighted in my post i think that about covers it . Turned a good bike into a horror

84ok said:

need to find the post but fullauto of course has the best answer imho, in another thread..

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I thought fullauto had a mikuni on his bike? I don't remember him posting about running a mk2 concentric hopefully he will chime in

I ride occasional with a buddy who has 2 of same bikes as me Duc ST3s and ‘72 Commando .... we both have single carbs on our Norton’s ... mine is Mikuni his is one of the originals that came on bike Amal ... both carbs set up well for our almost sea level riding .... neither of us has ever had any problems while out together on the Norton’s .... my bike does seem to pull harder and will break the ton no problem , his , I’m not sure .... while both have been trouble free he does seem to get better gas mileage .... plus I may have a more excitable right hand as he usually following regardless of which bikes we on ... conclusion : both work pretty well in my experience , I setup my Mik many years ago and other than draining bowl in late fall that really is only maintenance involved .... so I really like my single Mikuni VM34 way fast enough and pulls hard from still to thrill !
Craig

You see posts on here about people trying various carbs, both dual and single, and then throwing them away after a short while with nothing but problems and then declaring them junk. They would never use them again. The problem usually is that they are not jetted correctly. I know that with my VM 34 Mikuni, it was on the bike when I got it and I have done some 60,000 miles since, that it has been virtually trouble free in that time. I don't know about Anals,but my 850 will run very well over a broad range of jetting. I thought that I knew a little bit about jetting, but until I fitted an O2 sensor and gauge, I realised that I knew virtually NOTHING about the subject. Where I thought I was going the right way with jetting, the O2 sensor showed me that it was the WRONG way. Even a run on a dyno with a sniffer up its bum, showed that these things are not perfect either and showed that at lower throttle openings, the bike ran very lean. When I fitted the sensor, in the correct place, it showed exactly the opposite. I fitted the sensor to a spare set of pipes and planned to take it off when I found out what I wanted to know. However, it is such a useful device that I now plan on keeping it fitted.
People say "the bike was running rich, so I fitted a smaller main jet". This is generally wrong. To jet your bike correctly, you need to start with idle settings and work your way up, with main jet choice and air jet choice last. The air jet is not part of the low speed circuit, but a fine tuning method for the main jet. This is because the lower speed settings add fuel at ALL throttle openings, whereas main jet choice does not affect any of the low speed circuits. With my current settings, my 850 is an extremely pleasant, trouble free runner, with very good economy. 65mpg (Imperial). And, as people are aware, I am not interested in what happens in the top operating range of a Norton "powerband".

So, whatever carb setup, please take the time to jet correctly and I'm sure that whatever you choose, it will do the job well. Unless it's an Anal.

Oh, one more thing. The Mikunis generally come jetted very rich for the application, obviously so you don't seize your bike, so there is a lot to be said for correct jetting.

Fullauto, I too run a single Mikuni 34 on my 850

From your comments I am interested in finer tuning my jetting even though the motor runs just fine all over

Can you tell me where you got an oxygen sensor for tuning and some direction of how to use it? thanks!

Fullauto said:

Unless it's an Anal.

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I will never look at my carbs the same way again ----

1up3down said:

Fullauto, I too run a single Mikuni 34 on my 850

From your comments I am interested in finer tuning my jetting even though the motor runs just fine all over

Can you tell me where you got an oxygen sensor for tuning and some direction of how to use it? thanks!

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I did a search for O2 sensors and air/fuel ratio gauges on the internet and found a place in Texas. I think all up cost was about AU$200. It comes with a bung which needs to be welded on your header pipe about two feet down from the head. Don't forget to fit the exhaust nut before welding the bung on! I just used a velcro strip on my handlebar mount to attach the gauge and had my auto electrician mate wire it up. Then, it's a case of checking your numbers at various throttle openings and seeing where you are rich and where you are lean. Err on the side of caution of course. I aim for a fuel/air ratio of about 13.5 to 14 to 1. Others may have different ideas. It can be hard to see the readings in direct sunlight, but no problem on cloudy days, in tunnels, etc. A very interesting learning experience.
Our Nortons are not motorcycles but "learning experiences". You can see what is happening when you are cruising at a set speed and fine tune for economy if you wish.
Also available is the Sudco Mikuni tuning book. Very handy for understanding which bit does what and also has parts listed as well. A very useful resource. Enjoy and let everybody know what you learned.

baz said:

I thought fullauto had a mikuni on his bike? I don't remember him posting about running a mk2 concentric hopefully he will chime in

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yes single mik argument that settled for me any single vs dual arguments/considerations out there,

at least as far as street use goes

thanks Fullauto! In the meantime while I research to find a company can you please tell me what altitude you are at
and what your basic Mikuni jettings are, I am using the needle middle notch, 35 pilot jet, I believe stock slide 2 1/2?
have you found reason to deviate from stock suggested, vender supplied settings? thanks

Absolutely! My settings will be somewhat different to yours because of my cam and head. I will have to check but mine are leaner than what you are running. For example, I am running 32.5 pilot with a #3 slide with #230 main jet. I forget the rest, needle jet, needle and circlip position. You'll have to wait until I strip my card vnext. But, I would stress that these are MY settings, not for any other configuration. Fit your O2 sensor and all will be revealed.

Single Mikuni or single Amal ? I have had a lot of carbs in my years and only had one slide break off a chunk. I can only assume that it then went through my engine. It was an Amal. I was 100 miles from home and it would only run wide open.
You should be able to jet either of them to get a well running bike, but the Mikuni is a better machine. I tried twin VM 34s and never got it to run right. I am not saying that that is a bad combination, I am only saying that I could not get it right. I took one of the two and ran it as a single and that worked fine. Best of luck to you.

From a financial point, the Mikuni is less expensive as a unit versus the Mk11; a sub example is that the Mikuni idle jet can be purchased for about $3.50 US, the idle jet for the MK11 is about $17.00 US; the Mikuni calibrated parts are considerably more available, and there is a greater knowledge base for the Mikuni.

Esthetically, IMO, the MK11 appears to have a better exterior finish; both have the same type, and number, of calibrated parts, both are tuned essentially the same way.

it is hard to beat the Mikuni for value.

84ok said:

yes single mik argument that settled for me any single vs dual arguments/considerations out there,

at least as far as street use goes

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The question was "how does a single mikuni compare to a single mk2 Amal" there is nothing about single verses dual carburettors

Fullauto said:

I did a search for O2 sensors and air/fuel ratio gauges on the internet and found a place in Texas. I think all up cost was about AU$200. It comes with a bung which needs to be welded on your header pipe about two feet down from the head. Don't forget to fit the exhaust nut before welding the bung on! I just used a velcro strip on my handlebar mount to attach the gauge and had my auto electrician mate wire it up. Then, it's a case of checking your numbers at various throttle openings and seeing where you are rich and where you are lean. Err on the side of caution of course. I aim for a fuel/air ratio of about 13.5 to 14 to 1. Others may have different ideas. It can be hard to see the readings in direct sunlight, but no problem on cloudy days, in tunnels, etc. A very interesting learning experience.
Our Nortons are not motorcycles but "learning experiences". You can see what is happening when you are cruising at a set speed and fine tune for economy if you wish.
Also available is the Sudco Mikuni tuning book. Very handy for understanding which bit does what and also has parts listed as well. A very useful resource. Enjoy and let everybody know what you learned.

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I use a Koso narrow band on my norton
It does make it very easy to see what's going on with your fueling the bung needs to be welded into the downpipe 200mm from the head
I also mark my throttle drum to see exactly what circuit I am on
It is a bit of an eye opener when you can see exactly where you are rich or lean

baz said:

The question was "how does a single mikuni compare to a single mk2 Amal" there is nothing about single verses dual carburettors

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& plenty of folks feel strongly about 1 vs 2 from the get go, hence they chime in & it comes into the picture , as it has here,

whether u or op are interested in hearing anything further about it or not & can easily ignore,

at the same time, there is plenty of solid info in this thread already, with the one on one comparison if op is still inclined, including the individual carbs op asked about

84ok said:

& plenty of folks feel strongly about 1 vs 2 from the get go, hence they chime in & it comes into the picture , as it has here,

whether u or op are interested in hearing anything further about it or not & can easily ignore,

at the same time, there is plenty of solid info in this thread already, with the one on one comparison if op is still inclined, including the individual carbs op asked about

Click to expand...

Yes the single verses twin carburettor setup has been extremely well covered

In the 46 years of Norton ownership I have tried a lot of different combinations. I had the single MK 2 on a stock 850 and once jetted correctly I loved it. When I sold that bike I meant to remove it and reinstall the original twin Amals but the buyer offered up an additional $200 to leave it on. On my current '73 stock 850 I have the original type 32mm Amals (in a box) new Amal Premiers also in a box, and a Mikuni VM 34 on the bike. The reason that I have the Mikuni installed is for simplicity only. Overall performance seems to be on par with my old MK 2 setup and maybe slightly down from the Premiers but only on top end. Parts availability, price, and tunability helped determine going with the VM. No regrets. That said at some time in the future I'll probably reinstall the Premiers just for sh^ts and grins. I prefer a stockish Norton versus trying to wring the last bit of horsepower out of an antiqued engine. I learned THAT lesson back in the early 80s when I installed a Drouin supercharger on an 850. Bad operator management on my part lead to blowing the crank clean through the bottom of the motor. Traded the Drouin for a used motor and I've never strayed too far from stock. Recently when I felt the need for speed I'd jump on my BMW S1000RR. I sold that Beemer bad boy a couple of years back after a long counseling session from a county sheriff who fortunately was a customer of the BMW dealership that I worked for. Kept my license and avoided the BIG BIG HUGE ticket based on the promise of selling the bike. Crap, got slightly off of track. As for your Solex question, Pokes Cycle in Seattle was trying a side draft Weber conversion back in the late 70's. The Weber looked almost identical to the picture of the Solex. I don't think that they ever got it to carburate well. I do remember that same bike with a dual MK 2 setup that they were very happy with. My opinion is that I'd avoid the Solex. Why try to make something work when there are so many tried and true options available.

flatfan, who started this thread, wrote:
"Unfortunatly the bike didn´t have the original Amals when I bought it back after 30+ years, it was equipped with two Mikunis which are from a snowmobile engine I´ve been told. Probably made for 2-strokes. They probably work but I´m going for a single."

Sounds like he has never run the bike. Twin Mikunis are a valid carb option for a Norton, once they are jetted correctly.
https://www.mikunioz.com/shop/norton-750-850-commando-dual-vm34-carb-conversion-kit/?v=3e8d115eb4b3

I would run the bike and see how the twin Mikunis work before deciding to swap them out.

Stephen Hill