Mikuni carb

Any advice on switching from 2 amals to one mikuni on 1973 750 commando

My opinion is don't, Amal carbies are so simple, I don't know why people have so much troubles with Amal carbs, they do need to be maintained same as any other carbie, yes things wear, depends on how many mile you ride a year, how you ride your bike but going single carb you lose a lot of performance, over the 50 years of owning my Norton I gone down the road of changing the carbs on it but in the long run I have gone back to my old Amals and have found my Norton runs so much better with them, my 850 motor isn't stock built for the Featherbed frame, cam and head work, the Amals are jetted right for my motor performance and with the Joe Hunt magneto it starts first kick every time whether cold or hot, they are easy to maintain, easy to tune and I am no tuning expert but I do know my own bike.
But of course everyone is different and ride differently to how I ride, but if I was going to go down the road of new carbs a set of premier Amals be the go and they look better as well, tuned right they are a reliable carbie, simple to work on, jetted right for your motor and if timing is set right will be a one kick starter every time.
Pay a bit more and put on a set of Premier Amals and your Norton will love you for it, this is of course my opinion.

Ashley

The Amal premiers are way better than the old ones. And they look the part on Nortons. The downside is PRICE. And the need to synch them up and stay on top of them.
A single Mikuni is easy to start, just set them on fast idle, may or may not use the choke, and give it a good kick.
You will probably have to remove the ham can filter and make a new position for the key switch. Someone, somewhere, makes aham can to solve this problem.

I just acquired a '72 as well and thinking about switching. Especially after just hassling with the stock filter and the inner manifold fasteners. At 73, easy is the name of the game for both maintenance and starting. I read the single Mikuni helps in both departments. Have also read good things about the CNW kit.

Any comments? Appreciate the help from those more knowledgeful than I.

Mikunis are fine instruments, very well made. But you do have to be careful to not buy counterfeit these days.

A Mikuni that is set up well, will run very well on a Commando.

A Mikuni that is not, will not.

And… the same applies to Amal’s, set up right a pair of new Premiers will run superbly on a Commando and definitely outperform a single Mik above 5k rpm ish.

A single Mikuni kit will be cheaper than a pair of new Premiers. That and being easier to get on / off realistically the only advantages IMO. So if these issues are important to you, and performance above 5k rpm is not, a Mikuni makes an awful lot of sense.

I don’t run either now FWIW, I run FCRs as sold by cNw.

You will, of course, get many contradictory opinions on this topic. At the end of the day, it’s your call.

My 1973 850 came with a single Mikuni when I bought it.
It's very easy to start with its lever choke that is on the left side of the carb. I flick the choke on, start the bike ( I have an Alton Estart) and the moment it fires, I flick the choke off. It runs very, very poorly if I leave the choke on.
Interestingly, it did not idle well after starting when it had the Boyer ignition that came with the bike. When I changed to TriSpark ignition, and did not touch anything else, suddenly the engine idled well right after cold starts.

Dennis

My pile-O-parts N15CS came with a VM34 and the 2>1 adapter. I also have some Amals, and thought about running them, but the Mikuni is so good I that don't want to spend time and money to change for some performance increase. I'm not looking for speed out of the Norton; I have other bikes for that. I think having a 7.5:1 compression engine and tall gearing makes the Mikuni setup right for the task, whereas a Commando is a 'wring it out' vs. ride the down-low torque of my bike. I rarely go over 4K RPM, don't need to.

Advice ?
Get off the choke ASAP on the Mikuni . It's a rich situation , best flipped off soon . The manifold was not meant for high RPM's .
Also : attaching the manifold to the head , the 4 Allen screws need to be tight , with blue Locktite on the threads .

Torontonian said:

Advice ?
Get off the choke ASAP on the Mikuni . It's a rich situation , best flipped off soon . The manifold was not meant for high RPM's .
Also : attaching the manifold to the head , the 4 Allen screws need to be tight , with blue Locktite on the threads .

Click to expand...

Yep, or kick it over with the key off and enrichener on, that is all it takes on mine if it's cool out.

I believe that COMNOZ had stated that a 36 manifold worked better than the 34 manifold with a 34 carb.

I did the swap on my trident from the worn out amals to VM series miks, so not the same thing, but I don’t think I’d do it again. The kit I bought came “pre jetted” for the bike but in reality it was a lot of fiddling, moving the needles and changing jets till the bike ran right. Full disclosure- once it was dialed in it ran like a champ, but the convenience of the amals wasn’t there. I’ve done premiers on every bike I’ve rebuilt since, and it’s been money well spent. YMMV though, perhaps the commando single carb kits are better dialed in ‘out of the box’

ashman said:

My opinion is don't, Amal carbies are so simple, I don't know why people have so much troubles with Amal carbs, they do need to be maintained same as any other carbie, yes things wear, depends on how many mile you ride a year, how you ride your bike but going single carb you lose a lot of performance, over the 50 years of owning my Norton I gone down the road of changing the carbs on it but in the long run I have gone back to my old Amals and have found my Norton runs so much better with them, my 850 motor isn't stock built for the Featherbed frame, cam and head work, the Amals are jetted right for my motor performance and with the Joe Hunt magneto it starts first kick every time whether cold or hot, they are easy to maintain, easy to tune and I am no tuning expert but I do know my own bike.
But of course everyone is different and ride differently to how I ride, but if I was going to go down the road of new carbs a set of premier Amals be the go and they look better as well, tuned right they are a reliable carbie, simple to work on, jetted right for your motor and if timing is set right will be a one kick starter every time.
Pay a bit more and put on a set of Premier Amals and your Norton will love you for it, this is of course my opinion.

Ashley

Click to expand...

Thanks…..I tend to agree

Back in the late 79 my original Amals were quite worn, but the Norton still ran good just wouldn't idle without holding the throttle open a bit, so when I started the Featherbed conversion in 1980 a friend of mine was in the local Norton owners club and they ordered me a new set of Amal carbs, them days before the internet a lot more hassles and time to get parts from England, but after weeks of waiting 2 new Amals arrived but they were both left hand carbs, so one had to be sent back to get a right carb, was OK with that as I was still building the Commando/Featherbed, these 2 new Amals were made out alloy and not pot metal like the old Amals, to this day I am still running these Amals and the slides are still as good as the day I put these Amals on with a break in 2011 when I installed Jims PWK carbs, but have since gone back to my old Amals after 11 years of troubles with one PWK carb.
I replaced the Amals with the PWKs when I had the dreaded blocked pilot jet in the left Amal at the time so after 11 years I pulled the old Amals out and pulled them down and gave them a good clean, took 3 pull downs before the left Amal pilot jet was unblocked, that was 4+ years ago now and the old Amals are still running great.
So seems replacement Amals made out of alloy were around long before Premiers were around, at the time back in the 80s I only paid $100 for 2 new Amals and they are still as good as the day I put them on, but depends on how many miles I clock up in a year I do replace needles, jets and all O rings every 3 years or so, so these Amals have well over 110k miles on them with no wear what so ever on the slides, my original Amals were flogged out with just over 20k miles but I ended with just over 25k miles on them before I replace them.
By the way I worked with metal all my working life and do know the difference between pot metal and alloy metal and the slides on the Amals I am running with are harder than the original slides.

Ashley

Torontonian said:

Advice ?
Get off the choke ASAP on the Mikuni . It's a rich situation , best flipped off soon . The manifold was not meant for high RPM's .
Also : attaching the manifold to the head , the 4 Allen screws need to be tight , with blue Locktite on the threads .

Click to expand...

I would just add that the two inner bolts, if not tightened with blue locktite will vibrate loose and tumble down your intake! It has not happened to me, but I've read of it multiple times. My bike came with a VM36 and those two inner bolts were very loose and backing out when I checked them!

Franko;
Interesting that Comnoz found improvement using a VM36 manifold with a VM34 carb. He must've filled and re-drilled the carb mounting holes? The 36 flange is a little wider, so that would take some effort, but must be do-able. I take it, that was better than a VM36 manifold with a VM36 carb?

Edfury828 said:

I take it, that was better than a VM36 manifold with a VM36 carb?

Click to expand...

I do not belive so. I believe his point was that the manifold is the bottleneck.

are all manifolds created equal? NCW?

Fast Eddie said:

I do not belive so. I believe his point was that the manifold is the bottleneck.

Click to expand...

There's no bottleneck on my inlet manifold

Manu said:

are all manifolds created equal? NCW?

Click to expand...

The issue with the bolt on kits is that there is not enough space between the cylinder head and gusset of the frame to fit a well flowing manifold. Some people (like Baz) remove the gusset, and fabricate a better manifold.

But the bolt on kits have to work within the constraints of being ‘bolt on’ so no, I do not believe any are better or worse than others.