Mikuni or Amal Premiers? Which way to go?

Previously Jem Nicholls wrote:

I need to renew my carburattors yet again. I bought a new pair of Amal Concentrics 12 years/15000 miles ago thinking they'd be wonderful but they've been really disappointing. Long story short, one carb must be distorted because the (brand new) anodised slide is sticking and won't drop under return spring pressure despite the fact that it was fine when I put it on the bike. Well, fine for a while.

So I'm just about to go down the single Mikuni route which at £360 is a bit more expensive than 2 new Premiers (£285) but I get the impression a Mikuni is just a better solution. No flooding because it has a proper enrichening system, no balancing twin carbs, no crappy Amals always going wrong. I just want a carburettor that works. Full stop. Yes, I like originality but even more than that I'd like something that I don't have to continually fiddle with. I don't get to ride the Norton as much as I used to but there's always something wrong with these carbs. Arrgghh!

But has anybody actullay tried either route or even both? I'd welcome some honest opinions / feedback. Cheers

jem.

a single mikuni carb is a good replacement.i feel its a improvement on a Amal.

its not original but nether is my roadrider tyres and they are better than TT100,s

google rockypoint cycles in usa.A better price than over here.best if you know someone over there to pass it onto you as a gift. otherwise you will be walloped for import tax.

tony w

New Premiers are great and should be hard wearing.

A tight cable can cause a slide to hang up.

Hello Jem

You and I chatted carburettors many years ago at some international rally; can't remember which one, but some one was 'mooning' on a passing lake cruise at some time I recall. I said that a single carburettor stopped that roar from 5,000 to 6,000 RPM.

I have switched between a Mikuni 36mm and twin Concentrics many times.

The Minkuni can give lovely pick-up and easy running when cold or hot. The only pain for me was a difficult transition from starting on full choke when it was absolutely fine, to running with choke off. If you were on a steady 40-50 mph road then fine, but if you were still in a town then it was an absolute bugger for a few minutes until it was fully warm. I suspect that a tweeking of the choke jet and also the pilot jet might have sorted it. But that carb is now with someone else. I repeat, absolutely fine except for the cold to hot transition.

The problem with all the pre-Premier Concentrics was faulty pilot systems. Well, that's what I think. The fixed jets were too small and prone to blocking. I have just drilled mine out to a larger size and all seems good. But I need the Summer for a proper test. Hopefully these new Concentrics, with removable pilot jets, will be an answer to the stuttering pick up faults of all the fixed jet versions.

So, do you go for the new Premiers or not?

Norm

I can't understand the problems people seem to have with Amal concentric carburettors.

I have restored and run many Commandos and, as long as the known technical problems are dealt with, they seem to work fine.

Thoroughly clean all parts of the carbs and use an old steel guitar string and compressed air to clean the troublesome mixture run. Make sure that the slides run smoothly in the carb bodies. Run the tickover screws out until both slides are fully bottomed out. Make sure the floats are not punctured and are rising to the correct levels. Use Viton-tipped float needles. Use new gaskets.

One of the main challenges, as mentioned above, is the possibility of cable hang-up which causes the slide(s) to fail to fall in sync. When fitting the choke and throttle cables I split the cables at the junction boxes (not necessary if you fit from front backwards) and ensure that the cables for each carb run on the left/right side of the frame as appropriate. This method allows the cables to curve naturally with no tight spots with one choke and one throttle cable each side of the main frame tube. Make sure all cable end protectors are properly seated in carbs, junction boxes and adjusters. Leave a little slack in the throttle cable. Use the carb top adjusters to ensure that the slides and chokes start to rise at exactly the same time. Screw in the tickover screws until they touch the slides. Fully screw in the mixture screws and screw out 1 1/4 turns. Tighten the throttle cable top adjuster leaving about 2mm slack. Fit the carbs as per the manuals. Start the bike and adjust as per Bushmans. Finally remove nearly all slack from throttle cable using top adjuster.

Hi Jem I use Thackeray washers these prevent flange distortion I LOVE MY NEW PREMIERS will chat at the next club night Pete.

I too love my standard Concentrics â although it took me nearly 20 years to work out that they were set up wrongly! The ones fitted at present were new in 1999, have covered around 23,000 miles, and are still going strong â they had a lot of attention last year, including the installation of anodised slides, and they are stronger than ever. On the other hand, if I were in the market for new carbs now, I would probably try the Premiers, since they have similar appearance and a number of advantages.

Previously philip_baker wrote:

Thoroughly clean all parts of the carbs and use an old steel guitar string and compressed air to clean the troublesome mixture run.

Philip,

You are quite right, pay attention and they can be set up nicely. But it was when the Concentric manufacture went over to a fixed pilot jet and pressed in brass plugs to close the pilot passage that causes the problem - you cannot get that guitar string in to clear the jet.

There is also a difference in rider perception of a 'problem' and perhaps I am a fussy so-and-so. Some riders grab a handfull of throttle after shutting off and sit at a junction going blip-blip: they are not going to detect slight hesitation as you ease the throttle open from shut at a steady 30 MPH. That flat spot, which is a transition from the pilot jet into the cutaway, should not happen. It it does not happen to a lot of other Commandos on Concentrics. It may be an exaggerated defect in this particular Concentric manufacture which I bought in 2004. The shielded jet was added to overcome this type of problem.

Bushman's notes are very good. What I have now done is drill out the brass plug, and I opened up the pilot jets from the 0.016" (which Jim notes as the size) to a larger 0.019". I then fitted a blanking plug as Jim describes.

The effect has been that my airscrews are now 1 and 3/4 turns out, whereas they used to be 1 and 1/4. So there is more air going through the pilot system to match the 40% increase in fuel.

A medium test, fully warm, at the end of last year proved all was good. A longer evaluation this year will show if I have improved it. If not, they go in the bin and I get the new ones!

Norm

Previously norman_lorton wrote:

Previously philip_baker wrote:

Thoroughly clean all parts of the carbs and use an old steel guitar string and compressed air to clean the troublesome mixture run.

Philip,

You are quite right, pay attention and they can be set up nicely. But it was when the Concentric manufacture went over to a fixed pilot jet and pressed in brass plugs to close the pilot passage that causes the problem - you cannot get that guitar string in to clear the jet.

There is also a difference in rider perception of a 'problem' and perhaps I am a fussy so-and-so. Some riders grab a handfull of throttle after shutting off and sit at a junction going blip-blip: they are not going to detect slight hesitation as you ease the throttle open from shut at a steady 30 MPH. That flat spot, which is a transition from the pilot jet into the cutaway, should not happen. It it does not happen to a lot of other Commandos on Concentrics. It may be an exaggerated defect in this particular Concentric manufacture which I bought in 2004. The shielded jet was added to overcome this type of problem.

Bushman's notes are very good. What I have now done is drill out the brass plug, and I opened up the pilot jets from the 0.016" (which Jim notes as the size) to a larger 0.019". I then fitted a blanking plug as Jim describes.

The effect has been that my airscrews are now 1 and 3/4 turns out, whereas they used to be 1 and 1/4. So there is more air going through the pilot system to match the 40% increase in fuel.

A medium test, fully warm, at the end of last year proved all was good. A longer evaluation this year will show if I have improved it. If not, they go in the bin and I get the new ones!

Norm

Drilled my pilot jets out to 0.45mm, but no need to drill out the plugs when you can just remove the air screws to gain access to the pilot jets.

I glued the drill bit to a wd40 can straw and performed the drilling by hand.

Air screws now at 1 3/4 turns out and nice responsive throttle uptake.

Good luck!

Jem,

Been running Mikunis on most of my Commandos for years, downside is a slight loss of power in top gear overtake scenarios, if I need to change though I'd be very tempted with the premiers, authentic look and restored power with hopefully none of the pilot jet issues with the old ones.

Passing your way next Friday en route to the ferry!

Gino

I went to single mk1 Amal for the following reasons,- its a simple carb that I know well, plenty of cheap easy replacement spares, with the RGM narrow air filter it all looks pretty standard. With 2 cylinders sucking through one carb I don't think slide wear will be a problem. Through the seat of my pants it feels like there is a bit more torque at low revs, but it is a bit strangled at higher revs (where I don't go very often). Fuel comsumption is only a bit better, tickover is spot on reliable once the engine has been running 2 minutes.

Previously Jem Nicholls wrote:

Previously Chris Grimmett wrote:

Previously norman_lorton wrote:

Hello Jem

You and I chatted carburettors many years ago at some international rally; can't remember which one, but some one was 'mooning' on a passing lake cruise at some time I recall. I said that a single carburettor stopped that roar from 5,000 to 6,000 RPM.

I have switched between a Mikuni 36mm and twin Concentrics many times.

The Minkuni can give lovely pick-up and easy running when cold or hot. The only pain for me was a difficult transition from starting on full choke when it was absolutely fine, to running with choke off. If you were on a steady 40-50 mph road then fine, but if you were still in a town then it was an absolute bugger for a few minutes until it was fully warm. I suspect that a tweeking of the choke jet and also the pilot jet might have sorted it. But that carb is now with someone else. I repeat, absolutely fine except for the cold to hot transition.

The problem with all the pre-Premier Concentrics was faulty pilot systems. Well, that's what I think. The fixed jets were too small and prone to blocking. I have just drilled mine out to a larger size and all seems good. But I need the Summer for a proper test. Hopefully these new Concentrics, with removable pilot jets, will be an answer to the stuttering pick up faults of all the fixed jet versions.

So, do you go for the new Premiers or not?

Norm

If you are not worried about originality then Mikuni. JFDI. By the way, I was one of the two mooners; we couldn't resist the temptation knowing that the pair you were going past .....

Hi all,

I'm so pleased that "mooning" is a feature of this thread along with carburettor issues. Kind of puts things in perspecyives doesn't it? Put a load of blokes together, let them drink beer and they will eventually talk about motorcycles and bottoms! And no-one does that better than my good friend Chris G.

Whilst I was waiting for the next Solent Branch meeting to roll around (so I could natter more before buying a Mikuni) I thought I'd experiment with the existing Amals. Well, I'm retired now so time is not a problem. I took the new anodised slide from the RH carb and tried it in the LH carb: it stuck. I tried the anodised slide from the LH carb into the RH carb. It didn't stick. I'm NOT saying the new slides are different or wrong. As an ex-quality engineer I can remind you all that the complexities of surface form are deep. You have concentricty, straightness, cylindricity, circularity, high spots as well as diameter, surface finish etc. All these features are interacting especially on a used Amal where similar metals were used for the slide and carb body leading to wear and pick up after only a few thousand miles. What I've concluded is that putting brand new, undoubtedly within specification slides into a worn carb body does not work.

So I re-assembled the carbs with their old slides and I'll admit that there were various mating surfaces that had to be flattened first. And then I started the bike, third kick and it ran beautifully. It had stopped raining so a quick run to the pub was in order (of course) where it took 2 minutes to adjust the tickover, less time than drinking a pint. The ride home was bloody lovely!

That's not the end of the story, because Amals are very fiddely, everything has to be fettled, and I checked the run of the old slides before I started the bike and I know that occasionally one slide is still sticking open at WOT. But basically the Norton Commando is such a lovely bike to ride that I want to ride it more and going down the Mikuni route will make life easier. Hell, I'll probably buy some new Amal Premiers too and try them at some point to see how they compare.

In the meantime, it's back on the road and making me smile again.