Twin Amals or Single Mikuni?

simpson · Jan 31, 2013

Which is better for a 1971 Commando 750?

I have a friend who wants to trade even. Mikuni set up for the Amals.

Is there a clear-cut reason to go either way?

-simpson

Nortiboy · Jan 31, 2013

simpson said:
Which is better for a 1971 Commando 750?

Mikuni (34mm ?) is smooth down low with better Idle.

Twin Amals have a better top end.

Around town, Mikuni. Chasing mountains, twin Amals.

Then again, who wants a Commando breathing heathen air.

Dkt26 · Jan 31, 2013

I have a 36mm mikuni. It's ok round town w/ good lowdown response but runs out of oomph up higher rpm.
If you ride everyday to work as I do, try the mikuni as they are simple. I intend to ditch mine in the coming months as I've gone off the single carb look. I had originally purchased a mikuni 36mm flatslide pumper carb but it didn't fit so the VM36 was a crap compromise in my opinion.

concours · Jan 31, 2013

Multiple carbs (on ANYTHING) have always been a source of irritation for the mechanically challenged among us. If carbs are voodoo to you, the simple single may be your utopia. If, on the other hand, you are comfortable with the goings on in the carb, keeping them sync'ed doesn't give you the vapours, the deep breathing twins can be fullfilling. The fact that you are asking kinda suggests category #1. You tell US!? :mrgreen:

mike996 · Jan 31, 2013

Twin Amals. Sorted out they are as good as any other carb. Just don't expect a 40 year old, clapped out Amal (or any other carb) to be as good as a new carb.

simpson · Jan 31, 2013

I am comfortable with two carbs, building, jetting, synching, etc. Was just wanting to draw from the group's vast pool of knowledge and wisdom, whether anecdotal or otherwise...was really seeing if there was a good rule of thumb for this conversion.

-simpson

concours · Jan 31, 2013

simpson said:
I am comfortable with two carbs, building, jetting, synching, etc. Was just wanting to draw from the group's vast pool of knowledge and wisdom, whether anecdotal or otherwise...was really seeing if there was a good rule of thumb for this conversion.

-simpson

That was easy, the twins will give you a rewarding ride! enjoy :mrgreen:

Tim_S · Jan 31, 2013

And who doesn't like twins,,,,, of anything >> 8)

Tim_S

bmwbob · Jan 31, 2013

Swap with the understanding that you want to see how you like the Mikuni. I fought Amals for years that died at stop lights and seems poor ignition was issue. I have a single Mikuni and love it, but kept Amals as backup. I have an Aprilia 1000cc if I need top end speed :roll:

cjandme · Feb 1, 2013

Do the swap for the mikuni, ride the bike, later if you want twin Amals, get the new premier ones from Jerry here on the Norton Access store

P.S. I have the single flat slide set up from JSMotorsport which works well for me & my bike right now.

lrutt · Feb 1, 2013

Amals, but only if they are in good shape. If they are worn out then you need something new. Best thing is to get 2 new Amal Premiers

or you can cheap out a bit if all else is good on them and just drop in the new hard slides like I did. Great running machine with just that change alone.

mike996 · Feb 1, 2013

I posted on a recent similar thread that several years ago a friend and I did a side by side test of two 850s, one with a single Mik (don't remember the size) and my 850 with the twin Amals. At WOT in any gear, up to around 4-4.5k rpm there was no noticeable difference; beyond that the twin Amals ran off and left the single. We then switched carbs/manifolds between the bikes to be sure it was not just a stronger engine on one bike - the results were the same.

Whether the power above 4500 matters is up to you/how you ride. Obviously, as others have noted, a single is easier to deal with.

cmessenk · Feb 1, 2013

I switched to the Mikuni TM34 flat-slide back in 2009 and never looked back. Rock steady idle...1st kick start even after a month of sitting...removes from intake / air cleaner in seconds...and great performance. Don't be swayed by the claims of no "top end" performance...the slight difference (if at all noticeable) won't matter and, in my opinion, is just a function of how crazy you're willing to ride. I have no problem keeping up with my dual Amal Norton buds on weekend blasts. It will transform your riding experience and save tons of $$ on headache medication.

Dkt26 · Feb 1, 2013

lrutt said:
Amals, but only if they are in good shape. If they are worn out then you need something new. Best thing is to get 2 new Amal Premiers or you can cheap out a bit if all else is good on them and just drop in the new hard slides like I did. Great running machine with just that change alone.

I wouldn't swap for a second hand set of anals. They are likely to be worn and will give you the shits. Unless you have the anals and are swapping for the mikuni, that's a good deal as the mik has better wear factor than he old anals. Depends how much you like your buddy I spose?
New anals for a mik, yeah I'd go with the anals.

Spaulding · Feb 1, 2013

I've just switched from a single Mikuni setup to new twin Amals. Mostly because I wanted the stock air box back. So far I find them a bit trickier to deal with then the very simple Mik. But they seem to provide quicker acceleration, a more pronounced "note" (if that's possible), and certainly more punch at the top end.

I seem to have figured out the trick to a cold start and can get it going on one kick. But the Amals seem to flood very easily when trying to start after a short stop (like 10 minutes into the bank, for example). The bike didn't like those short stops either with the Mik, but rarely needed more than two or three kicks to come back to life. Don't recall flooding being an issue with the Mik. Hopefully I'll figure out what they like... Although it was weird and somewhat calming to take a nice little break to wait for a flooded bike to clear...

tpeever · Feb 1, 2013

I prefer the simplicity of the single Mikuni VM36 on my Commando but made the switch before I really knew very much about Amal carbs. I couldn't get my twin Amals to idle at all on my Commando. I got frustrated and went the single Mikuni route like a lot of people on this forum. The single Mikuni conversion is an excellent upgrade for the Commando IMO if you don't care about maximum performance. Having pretty much forgotten how my bike performed with twin carbs, I am now thinking about switching back just to compare. If I do ever go back to the twin Amals, I would not consider doing so until they were sleeved. I have restored several Britbikes with Amal Concentric and Monobloc carbs (all single carb bikes) and I had all of them sleeved by Lund Machine and they all work great. This makes me think that Amals CAN be good carbs if set up properly. I consider sleeving the Amal carb(s) to be a standard upgrade on vintage British bikes.

72westie · Feb 2, 2013

Why not dual Mikuni's?

concours · Feb 2, 2013

72westie said:
Why not dual Mikuni's?

Fat ass? The float bowl width will be close? Anyone know the center-to-center distance of Commando intake ports? I'd had this thought before...

The VM Miks are 3.283" wide at the bowl flange, if the port spacing is 3-1/2" or more, it should be a comfortable fit. Avaialable with left and right idle mixture screws for convenient twin mounting.

tpeever · Feb 2, 2013

I think there are people on here who have made dual Mikunis work. A cheaper and possibly better option would be to buy a set of the JS Motorsports carbs. I believe these are copies of Keihans but are flat slide rather than round slide? No doubt in my mind that Mikunis or Keihans are much better carbs than Amal. Better materials, better construction and they have an enrichener circuit which makes for much easier starting. This is not trivial considering the effort it takes to kick over a Commando especially as Commando owners get older.

With the single Mikuni VM36, my 850 starts second kick every time. First kick enrichener is on but no ignition, second kick enrichener and ignition on. Some people will never put anything Japanese on a Commando on principle so it all depends on how you want to ride, how much you enjoy synchronizing carbs, how much you care about originality etc. The single Mikuni is all about ease of starting and tuning and decent performance for average riding. As many people have told me, the two best things you can do to make yourself a reliable, sweet-running Commando are put an electronic ignition and a single Mikuni carb on it.

worntorn · Feb 3, 2013

As far as starting goes, I've had the opposite experience with Amals and Mikunis. I have four machines with Amal Mk1 Concentrics and all four are very easy starters, often one kick from cold and almost always one kick hot..
I have one bike with Mikuni conversion, it takes more effort to start. As crude as it is, the tickler on the Amals seems to be very effective at getting some fuel into the engine for cold starting. Two of the bikes also have chokes, but they aren't needed, the tickler does it.

Glen

Twin Amals or Single Mikuni?

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