I've been pricing up a single carb conversion - using one of my Amal Premiers...

Onder said:
For a road bike a single carb may well be better all around. Cannot see much difference up to mid range and that is where you spend most of your time. How much time do you spend above 5k?
But I suppose it depends on how you ride and where.
Click to expand...

Yep, I rarely rev it to 5k.

If it came in around say, £100 all in, I'd probably throw that at it just to try out and have the option, but I couldn't justify nearly £300.
 
Bonzo said:
Yep, I rarely rev it to 5k.

If it came in around say, £100 all in, I'd probably throw that at it just to try out and have the option, but I couldn't justify nearly £300.
Click to expand...
If you can live without the air filter box just fit a cheapo pod filter ,you could probably pick up a cheap 1-2 manifold off of eBay
You could use the throttle cable and choke cable you already have just by removing the short cable from the splitter box
All you'd need then is a fuel pipe
Be aware that some of the manifolds only use the two outer screws to fix to the head
And in this instance I've found it best to make my own one piece inlet gasket
 
I really don't want to stir up the single versus twin carb debate because it has been done to death
But if you rarely hit 5000rpm you will probably be better off with a single carb
It can make a commando more pleasant to ride with more low down torque and flexibility
And less balancing IMHO
 
Most punters that "I've" seen over the years that go for/try a two into one manifold set up generally struggle/hate/or can't set up or synchronize the carburetors correctly ....I did say most..🙂 ....not all....
I had good success years ago with a Stewart? manifold and a 34mk2 that I stuck on a mates bike....went well...
 
KiwiShane said:
Most punters that "I've" seen over the years that go for/try a two into one manifold set up generally struggle/hate/or can't set up or synchronize the carburetors correctly ....I did say most..🙂 ....not all....
I had good success years ago with a Stewart? manifold and a 34mk2 that I stuck on a mates bike....went well...
Click to expand...
One carb does stay in balance rather well I have found 😂😂😂
 
With road bikes most performance changes are ptobably purely subjective. You do not usually use the bike at full blast everywhere. so you probably never have a fair comparison. I have found that a restrictive exhaust system has much more effect than changes to the inlet tract, Wirh a 2 into 1 exhaust system which is only slightly restrictive, it is easy to lose 2000 RPM off the top of the usable rev range. Road-going Commandos do not usually rev to 7000 RPM. My 850 would go a long way past that, if I let it. A bigger carb on a 2 into 1 manifold should flow as nuch as separate carbs - the difference would be in the way the system resonates. At TDC when both valves are open there is flow across the top of the piston into the exhaust pipe, and back. With a single carb, that might not happen as efficiently. Silencers do not help resonance.
 
Tornado said:
My 850 came to me setup with single 932 fitted. It had the standard hamcan air cleaner with a single hole front plate. Ran the bike first couple of seasons like that and did appreciate the simplicity , but now run dual carbs and the bike just goes better. Sorting out balance and tuning took a steep learning curve for me, aided by using a carb balancer (Morgan Carbtune II).
Could not see myself going back to single (though I did fit it again briefly to help troubleshoot one carb against another).
I could be convinced to pop the single setup in a box and send it out to a new caretaker....
Click to expand...
Tornado,
I really like the way the CarbTune works. I haven’t had to adjust anything for quite a while.Once you get used to how it works the results are noticeable in a good way.
Mike
 
acotrel said:
With road bikes most performance changes are ptobably purely subjective. You do not usually use the bike at full blast everywhere. so you probably never have a fair comparison. I have found that a restrictive exhaust system has much more effect than changes to the inlet tract, Wirh a 2 into 1 exhaust system which is only slightly restrictive, it is easy to lose 2000 RPM off the top of the usable rev range. Road-going Commandos do not usually rev to 7000 RPM. My 850 would go a long way past that, if I let it. A bigger carb on a 2 into 1 manifold should flow as nuch as separate carbs - the difference would be in the way the system resonates. At TDC when both valves are open there is flow across the top of the piston into the exhaust pipe, and back. With a single carb, that might not happen as efficiently. Silencers do not help resonance.
Click to expand...
Its not just the single carb itself as a restriction. Apparently the common 2 in 1 inlet manifolds are not good for flow compared to two inlets.
 
Bonzo said:
Yep, I rarely rev it to 5k.

If it came in around say, £100 all in, I'd probably throw that at it just to try out and have the option, but I couldn't justify nearly £300.
Click to expand...
If you want my 2in1 manifold and single hole front hamcan plate, let me know what it is worth to you.
 
Tornado said:
Its not just the single carb itself as a restriction. Apparently the common 2 in 1 inlet manifolds are not good for flow compared to two inlets.
Click to expand...
That sounds reasonable.

I have a healthy CB750K6, 4 x Keihins, stock gearing. My lardy 850 mk3, with a 22T sprocket (might even be 23T, can't remember without checking) and a single mk2 Amal, is much quicker off the mark. I only take the Commando up to 6,000rpm and that high not very often. I have no doubt it out pulls the Honda up to that rev limit.

So, I'm really happy with a single carb's performance on the road and much prefer the easy set-up and maintenance (especially vs. 4 Keihins!).
 
I suggest a lot of guys kid themselves. With a road bike, if you tune it for maximim performance, when the weather changes - what happens if you have leaned-off the carburation ? - If the air gets hotter, the mixture richens and the motor slows. If the air gerts colder, the mixture gets leaner and the motor starts to miss. Most road bikes are faster in cold weather, because they are usually jetted rich. The difference between single and dual carbs is minimal. But a single carb is easier to live with. For racing, you are doing a different thing. If your bike is too slow, you simply adjust it. And you never worry about fuel consumption.
With motorcycles - they are usually designed to fulfil a certain purpose. And the rider adapts to the bike. A good bike makes a good rider. A bad bike creates bad habits in it's rider, but probably teaches you more.
Mike Hailwood started racing with the best bike, however I do not think he ever improved any motorcycle he rode. I met him. John Surtees was very different - he actually built racing motorcycles.
Agostini seems to have contributed to development.
 
"Mike Hailwood started racing with the best bike, however I do not think he ever improved any motorcycle he rode. I met him. John Surtees was very different - he actually built racing motorcycles. Agostini seems to have contributed to development."

I guess he improved their sales though, by riding round in those small circles quicker than anyone else :)

I'd hazard a guess he'd have been quick with a single carb, too. [attempt to bring it back to the subject matter...]
 
Back
Top