Dunstall: Performance Guru or marketing genius...?

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What puzzles me about the race engines of that era is that no one seemed to go above 32mm choke size , or maybe they did.
what carbs are you using on your Fullauto head? I have a Maney stage2 head to go on mine and am wondering what to use. Steve said they would have to be 34mm ...
 
oldmikew said:
What puzzles me about the race engines of that era is that no one seemed to go above 32mm choke size , or maybe they did.
what carbs are you using on your Fullauto head? I have a Maney stage2 head to go on mine and am wondering what to use. Steve said they would have to be 34mm ...
Click to expand...

I would go with Steve's suggestion if its an easy fit, if not, try boring your 32mms to 33mm.

My current Fullauto 32mm port set up is with 34mm Mikunis and 10.5" inlet tracts, it is 750 Short stroke. 36mm Mikunis or Amals would work too.

1975 set up was 36mm Amal Mk1s on 34mm ports, later changed to 34mm Amal MkIIs....which almost immediately were bored out to 36mm! Which just suited that 850 big ported and valved motor more.

So, some did use larger carbs (36mm max), but I think the most popular size was 32mm, known to be a bit restrictive at the top on a race motor, so 32s were often bored to 33mm, particularly for 'production racers'.
 
oldmikew said:
What puzzles me about the race engines of that era is that no one seemed to go above 32mm choke size , or maybe they did.
what carbs are you using on your Fullauto head? I have a Maney stage2 head to go on mine and am wondering what to use. Steve said they would have to be 34mm ...
Click to expand...

34mm on tapered ports is good. if the ports are over 32mm you might lose your midrange pulling power.
 
acotrel said:
what about the balance factor , Rohan? was it altered to stop the vibes killing the bike, or for rider comfort ?
Click to expand...

Same thing.
If the rider doesn't get vibrated apart, the bike is likely to hang together too.
And I wasn't there then, to see what they they did anyway.

We know you have your own pseudo science version of this, that only your x-ray vision can see,
but until you explain in words how this might work, we'll stick with conventional physics for now...

Otherwise, all engines would have the same balance factor, and forget about the rider - and things vibrating off and apart....
But we diverge, as usual, since you can't stay on topic.
 
SteveA said:
oldmikew said:
What puzzles me about the race engines of that era is that no one seemed to go above 32mm choke size , or maybe they did.
what carbs are you using on your Fullauto head? I have a Maney stage2 head to go on mine and am wondering what to use. Steve said they would have to be 34mm ...
Click to expand...

I would go with Steve's suggestion if its an easy fit, if not, try boring your 32mms to 33mm.

My current Fullauto 32mm port set up is with 34mm Mikunis and 10.5" inlet tracts, it is 750 Short stroke. 36mm Mikunis or Amals would work too.

1975 set up was 36mm Amal Mk1s on 34mm ports, later changed to 34mm Amal MkIIs....which almost immediately were bored out to 36mm! Which just suited that 850 big ported and valved motor more.

So, some did use larger carbs (36mm max), but I think the most popular size was 32mm, known to be a bit restrictive at the top on a race motor, so 32s were often bored to 33mm, particularly for 'production racers'.
Click to expand...
Thanks for the info Steve. What I thought were 32s probably had been bored out , its something that has always puzzled me. When I first bought my bike (new) it had 28.5 inlets and 30mm mk!s . It would do just over a ton . Fitting 32mms gave it
another 10mph without any subsequent work. Obviously there will be diminishing returns with just increasing carb choke size but am surprised more didnt emulate your example. The Works John Players that I saw only had 32 MK 1 or more probably
overbored to 33 .

Interesting also was Boughens comments about wanting to use an AMC clutch.. Almost certainly that would be the cause of gearbox failure.. Its a terrifying sight pull the primary outer cover start the engine , blip the throttle and watch the whole
shebang flex. A lighter clutch assembly would have been a better idea than moving from dot2 to dot 3 sleeve gear bearings which is what the factory have done.
 
acotrel said:
oldmikew said:
What puzzles me about the race engines of that era is that no one seemed to go above 32mm choke size , or maybe they did.
what carbs are you using on your Fullauto head? I have a Maney stage2 head to go on mine and am wondering what to use. Steve said they would have to be 34mm ...
Click to expand...

34mm on tapered ports is good. if the ports are over 32mm you might lose your midrange pulling power.
Click to expand...

My original 28mm head I eventually flowed and opened out to 32 will be interesting to see how that responds to larger carbs . The Maney head is basically for top end . You are right of course there is a trade with mid range . My current thinking is a toss between 34mm Amalmk 2s or 35mm Keihin Crs both of which will go in without splayed induction tracts.
 
The mostly stock looking factory 850 hotrod that Dave Rawlins and Mark Baker created that did the 143 mph 2 way average in 1973
had the Amals opened out to 33 mm. That was based on the stock carbs, so that was about as far as they could go with them.

The bigger 1000 amals that are 34 mm and larger are physically a LOT wider, so won't readily fit in between the frame tubes of a Commando.
That alone would have stopped any serious experimenting with larger carbs on Commandos. ?
If Amals had made 934 or 936 carbs, who knows what might have been. ?
Not forgetting these are old long stroke big bangers, so don't take the instant big gulps of air that much later short strokes do...
 
Rohan said:
The mostly stock looking factory 850 hotrod that Dave Rawlins and Mark Baker created that did the 143 mph 2 way average in 1973
had the Amals opened out to 33 mm. That was based on the stock carbs, so that was about as far as they could go with them.

The bigger 1000 amals that are 34 mm and larger are physically a LOT wider, so won't readily fit in between the frame tubes of a Commando.
That alone would have stopped any serious experimenting with larger carbs on Commandos. ?
If Amals had made 934 or 936 carbs, who knows what might have been. ?
Not forgetting these are old long stroke big bangers, so don't take the instant big gulps of air that much later short strokes do...
Click to expand...

Yes I remember it ... And what you say about the 1000 series is very true they are a massive carb. And long stroke engines
do of course have more time to breath so do not necessarily require such large chokes. Do not know whether US practice was any
different.
 
Rohan said:
The mostly stock looking factory 850 hotrod that Dave Rawlins and Mark Baker created that did the 143 mph 2 way average in 1973
had the Amals opened out to 33 mm. That was based on the stock carbs, so that was about as far as they could go with them.
Click to expand...

That hotrod engine ended up in Dave Sadler's Metisse with bigger carbs, Baker/Rawlins may have been constrained by class rules. Boring out 32s was fairly popular, easy, cheap and easy fit on a Commando frame. Bigger carbs were more often used on race frames.

The mainly ex Thruxton trick parts that became my engine had been collected together by Baker and Sadler and were intended to go into an engine for Sadler's Metisse, then Norton folded and he was redundent. He went of to mechanic for Alex George. Rawlins told me Sadler had an 'engine' for sale....he didn't tell me I would have to build it myself!
 
oldmikew said:
SteveA said:
oldmikew said:
What puzzles me about the race engines of that era is that no one seemed to go above 32mm choke size , or maybe they did.
what carbs are you using on your Fullauto head? I have a Maney stage2 head to go on mine and am wondering what to use. Steve said they would have to be 34mm ...
Click to expand...

I would go with Steve's suggestion if its an easy fit, if not, try boring your 32mms to 33mm.

My current Fullauto 32mm port set up is with 34mm Mikunis and 10.5" inlet tracts, it is 750 Short stroke. 36mm Mikunis or Amals would work too.

1975 set up was 36mm Amal Mk1s on 34mm ports, later changed to 34mm Amal MkIIs....which almost immediately were bored out to 36mm! Which just suited that 850 big ported and valved motor more.

So, some did use larger carbs (36mm max), but I think the most popular size was 32mm, known to be a bit restrictive at the top on a race motor, so 32s were often bored to 33mm, particularly for 'production racers'.
Click to expand...
Thanks for the info Steve. What I thought were 32s probably had been bored out , its something that has always puzzled me. When I first bought my bike (new) it had 28.5 inlets and 30mm mk!s . It would do just over a ton . Fitting 32mms gave it
another 10mph without any subsequent work. Obviously there will be diminishing returns with just increasing carb choke size but am surprised more didnt emulate your example. The Works John Players that I saw only had 32 MK 1 or more probably
overbored to 33 .

Interesting also was Boughens comments about wanting to use an AMC clutch.. Almost certainly that would be the cause of gearbox failure.. Its a terrifying sight pull the primary outer cover start the engine , blip the throttle and watch the whole
shebang flex. A lighter clutch assembly would have been a better idea than moving from dot2 to dot 3 sleeve gear bearings which is what the factory have done.
Click to expand...

I use the AMC clutch with single row primary chain on my 850. It is OK for racing on short circuits. That clutch has been used on 1000cc Vincent sprint bikes and sidecars, so it can handle the torque.
 
First man to use disc brakes on motorcycle :?:

hello lionel well as you see my name is Dixon does that ring any bells , Well my father was an engineer and a boiler inspector and he was freind with Denis Parkinson and his dad Bill Parkinson there Garage and sales room was at Ings Road Wakefield ,And there My great Uncle Freddie Dixon he was a Pionneer of motorcycles and car racing He was the frist man to use Disc Brakes in 1923,
from;

http://www.nortonownersclub.org/noc-cha ... /958198253

https://en.wikipedia.org/wiki/Freddie_Dixon
 
Bernhard said:
First man to use disc brakes on motorcycle :?:

hello lionel well as you see my name is Dixon does that ring any bells , Well my father was an engineer and a boiler inspector and he was freind with Denis Parkinson and his dad Bill Parkinson there Garage and sales room was at Ings Road Wakefield ,And there My great Uncle Freddie Dixon he was a Pionneer of motorcycles and car racing He was the frist man to use Disc Brakes in 1923,
from;

http://www.nortonownersclub.org/noc-cha ... /958198253

https://en.wikipedia.org/wiki/Freddie_Dixon
Click to expand...


OK...Hydraulic disc brakes.....on a solo motorcycle....

Lazy of me because I know about Freddie Dixon and his sidecar....

But I did say...generally attributed to....
 
SteveA said:
Bernhard said:
So, it doesn’t count because the sidecar was bolted on :?:
Click to expand...

Not what I said at all......
Click to expand...


OK, I misunderstood.
And no, they were not hydraulic operated, the first hydraulic operated disc brake came on I think the rear of an Harley Davidson on what looked like a calliper off a Chevy in the late 1950s :?:
 
SteveA said:
Rohan said:
The mostly stock looking factory 850 hotrod that Dave Rawlins and Mark Baker created that did the 143 mph 2 way average in 1973
had the Amals opened out to 33 mm. That was based on the stock carbs, so that was about as far as they could go with them.
Click to expand...

That hotrod engine ended up in Dave Sadler's Metisse with bigger carbs, Baker/Rawlins may have been constrained by class rules. Boring out 32s was fairly popular, easy, cheap and easy fit on a Commando frame. Bigger carbs were more often used on race frames.

The mainly ex Thruxton trick parts that became my engine had been collected together by Baker and Sadler and were intended to go into an engine for Sadler's Metisse, then Norton folded and he was redundent. He went of to mechanic for Alex George. Rawlins told me Sadler had an 'engine' for sale....he didn't tell me I would have to build it myself!
Click to expand...
 
SteveA said:
Rohan said:
The mostly stock looking factory 850 hotrod that Dave Rawlins and Mark Baker created that did the 143 mph 2 way average in 1973
had the Amals opened out to 33 mm. That was based on the stock carbs, so that was about as far as they could go with them.
Click to expand...

That hotrod engine ended up in Dave Sadler's Metisse with bigger carbs, Baker/Rawlins may have been constrained by class rules. Boring out 32s was fairly popular, easy, cheap and easy fit on a Commando frame. Bigger carbs were more often used on race frames.

The mainly ex Thruxton trick parts that became my engine had been collected together by Baker and Sadler and were intended to go into an engine for Sadler's Metisse, then Norton folded and he was redundent. He went of to mechanic for Alex George. Rawlins told me Sadler had an 'engine' for sale....he didn't tell me I would have to build it myself!
Click to expand...

If you have only fitted 1mm larger carbs and gained a 10 mph increase in top speed, I suggest you have altered the jetting. If you fit larger carbs and taper the inlet tract to maintain velocities within the port, the midrange will probably be better. The next thing is to gear the bike right to suit your application. If you can get an increase in mid range power, increase the overall gearing and use even a 4 speed close box - the bike will be initially difficult to get rolling, however once mobile will accelerate much faster. I always try to stay away from raising the operating rev range of my commando motor. I always concentrate on improving it's pulling power. I suggest a lot depends on the shape of the torque curve. I've found my bike is much quicker if I stay within a certain part of the rev range (5,500 to 7000 RPM ). There is really nothing in the motor to make it go fast except I use methanol fuel and a 2 into one exhaust. It is quick enough to win races and that astounds me. I never really appreciated just how good commando motors really are.
 
I have found gearing the commando-engined bike very deceptive. On one occasion I raised the gearing and the bike accelerated faster. If you don't try to make the bike pull, you don't find out what is happening in the middle of the operating rev range. The motor always seems to spin up at much the same rate regardless of the gearing. A short-shift on upwards gear changes often doesn't tell you much because the separation of the gears in a standard box is too great. The worst aspect of the standard box is the difficulty in doing smooth down-shifts. It probably doesn't matter much with a touring bike, however with a racer it is terrible (dangerous in the wet).
 
Bernhard said:
SteveA said:
Bernhard said:
So, it doesn’t count because the sidecar was bolted on :?:
Click to expand...

Not what I said at all......
Click to expand...


OK, I misunderstood.
And no, they were not hydraulic operated, the first hydraulic operated disc brake came on I think the rear of an Harley Davidson on what looked like a calliper off a Chevy in the late 1950s :?:
Click to expand...

I didn't think any American cars had disk brakes on the fifties except Crosleys.
 
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