Single carb (again)

worntorn · Apr 28, 2020

Craig said:
there are always exceptions , eh .... you sure they original, just askin' .... also, most interesting take away for me was the real world performance testing , I always thought my Mik equipped bike was performing as well or better than the twin Amal equipped bikes was with at times , but it was always same old story the original equipped twin Amal bikes are faster and quicker, from most even on this forum , the minority with singles sang an unheard song , nice to see some real world testing, vindication after personally feeling and seeing the improvement over the years ... I rarely hit 6500 rpm so as I have said for years , right set up for my type riding ... looks like from this piece I was correct .... and yup it nice to have that rock steady idle , that is mentioned too

Yes, originals. The original owner kept all bills for work done plus I chat with him now and then.
The slides are a bit loose now but the bike runs great, so I'm leaving it alone.

Glen

luckyed · Apr 28, 2020

I’m with worntorn and jbruney. ‘72 750 19,000 on original 932s. Slides slightly worn. Rebuilt when acquired with needle jets and needles along with float needles. Stock jets and set up. Starts first kick, idles like worntorn video steady at 1000 rpm. Rolls on with a steady big twin “blaaatt!” through the Dunstall exhaust right up to redline. Interestingly however, I changed out to the single Mikuni on my ‘71 that I had in the ‘70s, probably due to reading that article posted above, although I can’t remember why really. Can’t add anything to the performance comparison due to further faulty memory of details from that era.

luckyed · Apr 28, 2020

Now that I’m thinking about it , I believe that I knew those guys at “Do-it Engineering” mentioned in the article. I lived in the same area at the time. A transplanted Brit who did some engine work for me was either part of the operation or friends with the guys who put out the kit.

jbruney · Apr 28, 2020

Well... mine are far from perfect, but they do perform great about 98% of the time... There are times they need attention.

Fullauto · Apr 28, 2020

Even at the time it was said that Amals were only made to last the warranty period.

robs ss · Apr 28, 2020

Fullauto said:
Even at the time it was said that Amals were only made to last the warranty period.

It is virtually impossible to design something for a fixed life - or even a calculated minimum life.
You've been listening to too many "furphies" at the water cart.
Not saying that those old things weren't made of crap metal though...

Fullauto · Apr 29, 2020

robs ss said:
It is virtually impossible to design something for a fixed life - or even a calculated minimum life.
You've been listening to too many "furphies" at the water cart.
Not saying that those old things weren't made of crap metal though...

I think you have taken me too literally. It was a saying at the time to allude to the fact that they were rubbish.

concours · Apr 29, 2020

I need to thank Dad here.
For teaching me the science & theory of carburetors as he repaired them.
Sometimes on the kitchen table (winter in New England) lined with newspaper.
It’s allowed me to carry on fixing them.
And, not be “afraid” or “hate” multiples.

I think the Amal twin carbs are part of the iconic Commando look, just as much as the pee shooters, 19” wheels, forward inclined parallel twin. JMWO

concours · Apr 29, 2020

....and, I completely understand owners that struggle with them, and don’t blame them a bit, for just wanting a bike they can enjoy, without having to learn carburetor skills. That’s fair.

worntorn · Apr 29, 2020

It turns out that almost all motorcycle carb bodies and many automotive carbs are made out of the same basic zinc alloy.
I've heard it said that Concentrics are made out of " Monkey metal"
It may be, but it's the same stuff as used in Monoblocs and also similar to
the Mikunis, Keihins etc.
One nice feature with the Mikuni is the chrome slide.
On the other hand, with good air filters fitted 26 k is no problem for the Monkey metal slides.

With the anodized slides on the new Premieres, slide wear is no longer a concern.

I wonder how long the Mikuni slides would last? They look as though they would go forever, however I have seen some very high mileage Mikuni slides with chrome worn through and bodies worn out. The owner claimed they had about 70,000 miles on them, although he was unsure on that( speedo problems)

Glen

Craig · Apr 29, 2020

So far I have not done anything to my Mikuni , other than drain it at end of year , no idle adjust, no cleaning, no cable adjust etc. , literally nothing , didn’t even have to rebalance it , haha! .... have said for years on here that I was very happy with the Mikuni in all ways , and every time there were more detractors posting than support , almost always pointing to way better performance , nice to see at least someone else has real results , even if it was more than 40 yrs ago , Glen I applaud you and the rest that have stuck with the originals for many reasons ! They do look much better with the ham can and all ...

jbruney · Apr 29, 2020

My old wing's Keihin carbs are zinc alloy and at near 60k the alloy body exhibits no visible wear from piston travel.i This is an current observation as the overhaul of little pleasure winds down.

cliffa · Apr 29, 2020

jbruney said:
My old wing's Keihin carbs are zinc alloy and at near 60k the alloy body exhibits no visible wear from piston travel.i This is an current observation as the overhaul of little pleasure winds down.

Apologies up front here for going completely off track, but I think there is also a popular single carb mod for Wings as well? I seem to remember it's a VW downdraft carb on a custom manifold.

jbruney · Apr 29, 2020

Just stating that this particular alloy hasn't brought about the end of the world as we know it because it appears to be commonplace by most for the period... A bit of care is called for when working with it and keeping wear surfaces reasonably clean, which is maintenance most don't care for. Single carb is great providing one gets the bugs ironed out IMO.

dantriumph · Apr 29, 2020

I had a single Mikuni on my mk3, it ran great and slightly slower at top speed then a friends 850 with twin Amal. However it was worn out after 50.000km. Slide would stick at around 110-120km/h.
I've got a SU kit in a box somewhere in the garage, if anyone fancy having a go.
Dan

acotrel · Apr 29, 2020

There must be better carbs than Mikuni or Amal for single carb on a road bike. Something with better compensation for air pressure and temperature ? What about those injectors on Enfields ?

Staytite · Apr 30, 2020

On this wet rainy day I'm cleaning my computer

And came across this historical article on fitting an SU to a Commando (sorry could not get .pdf page to copy over)

PHOENIX

MAYBANK HOUSE HOPE STREET WORDSLEY

10T0RCYCLES LT
SU CARBURETTER- CONVERSION K I T - NORTON COMMANDO

STOURBRIDGE WEST ENGLAND

MIDLANDS

D Y 8 5Q B

FACILITY AIRPORT 14 & 26.

Phoenix Motorcycles..Limited arenow able to supply this kit, suitable for Norton Commando 850 and 750 models.

Development work on our chassis dynamometer, and during extensive road testing under all types of weather conditions has been completed.The special version of the superb SU HIF6 carburetter has been finalised by ourownengineersinco-operationwith experts from SUFuel Systems.

Many Norton enthusiasts will be aware that, prior to its closure in 1976, the Norton factbry had developed new versions o f the Commando fitted with an SU HIF6 carburetter. Although very successful and scheduled for prod- uction, t h e works found i t necessary t o make changes t o t h e frame. This virtually eliminated any hope of conversion by owners of earlier models.

Phoenix have, thanks t o experience j , with other successful conversions, now produced a kitwhich can be •Fitted without frame modification.^^

We have no less than three works Nortons with SU carburetters,and hold development data fromthe Norton works development programme

Our own Commando Mk2a, illustrated, tested over a n extended and varied period ofroad use, gave thevery impressive results below;

Average o f 8 tests... 79.05 miles per gallon.
.Worst figure ...67.5mpq (making useof thefull potential of the

850 Commando).
On-the-road power and speed arecomparable with twin-carburetter models, but tractability isgreatly improved and throttle response from aslow as 1000RPM intopgear issuperb. Idling ismore reliable and the.well known fiddling andbalancing ofthetwin carbs iseliminated. TheSU is virtually a "set and forget" instrument, made to operate over an extended period i n applications where frequent adjustment i s totally unacceptable.

cliffa · Apr 30, 2020

Staytite said:
On this wet rainy day I'm cleaning my computer

And came across this historical article on fitting an SU to a Commando (sorry could not get .pdf page to copy over)

PHOENIX

MAYBANK HOUSE HOPE STREET WORDSLEY

10T0RCYCLES LT
SU CARBURETTER- CONVERSION K I T - NORTON COMMANDO

STOURBRIDGE WEST ENGLAND

MIDLANDS

D Y 8 5Q B

FACILITY AIRPORT 14 & 26.

Phoenix Motorcycles..Limited arenow able to supply this kit, suitable for Norton Commando 850 and 750 models.

Development work on our chassis dynamometer, and during extensive road testing under all types of weather conditions has been completed.The special version of the superb SU HIF6 carburetter has been finalised by ourownengineersinco-operationwith experts from SUFuel Systems.

Many Norton enthusiasts will be aware that, prior to its closure in 1976, the Norton factbry had developed new versions o f the Commando fitted with an SU HIF6 carburetter. Although very successful and scheduled for prod- uction, t h e works found i t necessary t o make changes t o t h e frame. This virtually eliminated any hope of conversion by owners of earlier models.

Phoenix have, thanks t o experience j , with other successful conversions, now produced a kitwhich can be •Fitted without frame modification.^^

We have no less than three works Nortons with SU carburetters,and hold development data fromthe Norton works development programme

Our own Commando Mk2a, illustrated, tested over a n extended and varied period ofroad use, gave thevery impressive results below;

Average o f 8 tests... 79.05 miles per gallon.
.Worst figure ...67.5mpq (making useof thefull potential of the

850 Commando).
On-the-road power and speed arecomparable with twin-carburetter models, but tractability isgreatly improved and throttle response from aslow as 1000RPM intopgear issuperb. Idling ismore reliable and the.well known fiddling andbalancing ofthetwin carbs iseliminated. TheSU is virtually a "set and forget" instrument, made to operate over an extended period i n applications where frequent adjustment i s totally unacceptable.

Look in the Technical section on this very site, and you'll see the docs. down at the bottom. (Some kind soul donated them)

Staytite · Apr 30, 2020

Ah ha .... and you were that kind soul

Single carb (again)

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