Downdraft .

Status
Not open for further replies.
I didn't even need to scroll up to know that was A Graham Bell.

Its never going to happen on a stock Commando frame and the reason why the side draft version of the FCR can not have the float bowl level anywhere near optimum.
 
There are three main differences between a Commando cylinder head and a Triumph Bonneville head. The ports in the Triumph head have less down angle, and they are angled out wider in the horizontal plane. The Triumph head also has no squish band. The Norton head is much better than the Triumph head - which one of those differences do you attribute that to - or is it all of them ?
 
You can scratch around for years trying to find ways of improving the Norton cylinder head to get more power. A much better way would be to fit a decent Engine Management System and a better gear box.
 
acotrel said:
You can scratch around for years trying to find ways of improving the Norton cylinder head to get more power. A much better way would be to fit a decent Engine Management System and a better gear box.
Click to expand...
dannysengineportal.com

Throttle Position Sensor (TPS) - Function - Failure - Testing

Identify and fix throttle position sensor (TPS) issues to ensure proper start up and smooth throttle response in your vehicle.
dannysengineportal.com dannysengineportal.com

Wal Phillips fuel injectors were around in the 1950s.

MoTeC

Default Meta Description
www.motec.com.au www.motec.com.au
 
Time Warp said:
I wonder why Weslake was not involved with Norton development in the later period. (over the 'car people Cosworth)
Click to expand...
Bear in mind that at the time Weslake had been working with Rickman et al on Triumph based 4 valvers, and Cosworth was winning everything in F1.......
 
I am of the opinion that the Commando engine is excellent in standard form. When you use Amal or Mikuni carbs and petrol, it is difficult to get the tuning fine enough to get best power. I cheat - I use methanol fuel. The allowable margin for error is much bigger. If you read up om modern superbikes, a lot of performance is gained by using advanced fuel injection and ignition systems which control the richness of the mixture very closely. If you jet your Amal carbs closer to the optimum, you would probably be in the situation where the two-stroke guys were in the early 70s. You would always be working on your carburation.
I found three things from racing my Seeley 850 - If the mixture is the slightest bit too rich, the motor is noticeably sluggish. If the gear ratios are not close, the motor is noticeably sluggish. If the steering geometry of your bike is not right, you cannot power through corners My motor is fast enough to beat methanol-fuelled 1100cc CB750 Hondas. You should be able to get your Commandos going as quick on petrol.
 
You can scratch around for years trying to find ways of improving the Norton cylinder head to get more power. A much better way would be to fit a decent Engine Management System and a better gear box.
Click to expand...

INDEED , The Trans itself was a trifle fragile . every second year since 1960 they stated theyed upgraded the materials & changed the gear tooth form . Three or Four times , anyway .
Some Cowboy racing a Triumph in small town USA came up with a ' outrigger bearing ' . A slipper tensioner & Fixed box & bearing woulda bina cheap fix . A adequate trans unbreakable
WITH the outriger / Mainshaft / Clutch support bearing'd be MUCH BETTER . One can ave a outer clutch support bearing as well as a twixt sprocket one . But a 1922 gearset might be a bit off .
Being as they were all designed for 500's on licorice tyres & unseled roads ! .

As mosty wallopers couldnt MAINTAIN a Auto Adv & set of points ( & likely still cant ) a decent ignition system mightve save have the ' british trash ' that blew up becuse of that ,
and the other half that blew up because you wouldnt lend them your car , either . No REV LIMITER .

A decent ignition cut out wouldve averted many a 18 year old d*ckhead destroying a perfectly good motorcycle . Neglect abuse & incompetance after 5 years had done most in , in NZ at least .
Aus seems more like the US , when it wouldnt run right , it was parked . Unfortunately mostoffem live in sheds here . dismantled or otherwise . Not on the road .

Maybe there should be a aptitude test before someone can buy a spanner !
 
Last edited:
Gees . You could get at least 10.000 RPM with These Things !

Downdraft .

Gurney ran these things on his PR . APPARENLY YOU HAD TO HAVE GAS IN THE TANK & THE FUEL ON , OR THEY WOULDNT WORK . :oops:

Downdraft .

Where were we , Wal ,
Downdraft .
Downdraft .
souns like there mightnt've been a lot of FUEL PRESSURE ! probly for someone who can set a Float Level .
 
baz said:
I had assumed the Wal Phillips injector's were right up there with fuel management systems!!!!!!
Or dripping taps???
Click to expand...
If you are involved in historic racing, you might think differently. It all depends on eligibility. If you had an engine management system with pump on an historic racer, you would need injector bodies from the era of the bike or earlier. Some of the guys who race two strokes in Australia use a complete system off a go-kart, and still don't get pinged.
 
Matt Spencer said:
INDEED , The Trans itself was a trifle fragile . every second year since 1960 they stated theyed upgraded the materials & changed the gear tooth form . Three or Four times , anyway .
Some Cowboy racing a Triumph in small town USA came up with a ' outrigger bearing ' . A slipper tensioner & Fixed box & bearing woulda bina cheap fix . A adequate trans unbreakable
WITH the outriger / Mainshaft / Clutch support bearing'd be MUCH BETTER . One can ave a outer clutch support bearing as well as a twixt sprocket one . But a 1922 gearset might be a bit off .
Being as they were all designed for 500's on licorice tyres & unseled roads ! .

As mosty wallopers couldnt MAINTAIN a Auto Adv & set of points ( & likely still cant ) a decent ignition system mightve save have the ' british trash ' that blew up becuse of that ,
and the other half that blew up because you wouldnt lend them your car , either . No REV LIMITER .

A decent ignition cut out wouldve averted many a 18 year old d*ckhead destroying a perfectly good motorcycle . Neglect abuse & incompetance after 5 years had done most in , in NZ at least .
Aus seems more like the US , when it wouldnt run right , it was parked . Unfortunately mostoffem live in sheds here . dismantled or otherwise . Not on the road .

Maybe there should be a aptitude test before someone can buy a spanner !
Click to expand...
I have only ever peaked my motor out in first gear and dumped the clutch, on one occasion. I expected to spread the box on the start line and get hit from behind. It stayed together, but I would not like to do it too often, From memory however some of the Vincent sidecar guys used to cut the gearbox off the Vincent ,motor and use a Norton box.
 
Funny Looking Commando .

Downdraft .

egli-vincent.net

The Curtis-Vincent

Denis Curtis started to race in 1965 on a stock BSA 350 Gold Star that had been lent to him by a friend. Like many at that time, Denis often rode the bike to Cadwell Park, Lincolnshire, taped-up th…
egli-vincent.net egli-vincent.net

Can be to get rid off the heavy slow shifting cogs . The funny clutch . the triplex primary chain ,
or somebody mightve whacked it off to use the motor in a racing speedboat .

Or something mightve fallen off the back of a R A F truck .

Downdraft .


Aparently a few of these flew off into the desert . So if you see a Arab on a Norvin , it may well explain it .

Early tyres & dusty tracks wouldnta stressed the trans out like modern sticky everthings . A cush drive hub'd help .
 
Matt Spencer said:
Funny Looking Commando .

Downdraft .

egli-vincent.net

The Curtis-Vincent

Denis Curtis started to race in 1965 on a stock BSA 350 Gold Star that had been lent to him by a friend. Like many at that time, Denis often rode the bike to Cadwell Park, Lincolnshire, taped-up th…
egli-vincent.net egli-vincent.net

Can be to get rid off the heavy slow shifting cogs . The funny clutch . the triplex primary chain ,
or somebody mightve whacked it off to use the motor in a racing speedboat .

Or something mightve fallen off the back of a R A F truck .



Aparently a few of these flew off into the desert . So if you see a Arab on a Norvin , it may well explain it .

Early tyres & dusty tracks wouldnta stressed the trans out like modern sticky everthings . A cush drive hub'd help .
Click to expand...
S'funny innit?
Great article but not one mention of "downdraft"
Go figure?
;)
 
SEEING CERTAIN PEOPLE HAVE A TENDANCY TO BE A TRIFLE PEDANTIC ,

Downdraft .
Downdraft .


Downdraft .


1963 till 1976 , apparently . Maybe the poms couldnt afford a hacksaw & welding gear , back then . " The New British 1000 FOUR . ' Oh Dear . missed the boat, again .

Downdraft .

Cross - Flow , Even . That ( hillman ) is a close relation , of the Coventry Climax . Now , if BSA had done it , with there Bantam Bushman , They couldve called a Hillclimber a BSA HILLMAN ! .

Downdraft .
Downdraft .
nuther boat missed . anyone frown a T 120/T40 in one , & Does a T 150 / R III Fit ? .

The Answer , to the First , at least . . .

Downdraft .


But its a parrallel Port Bonne head ( were told ) , youd need a R III or T 160 , to get a bit of DOWNDRAFT . Cor. whadaya expect with a name like SS , you wouldnt really call them ' Friendly ' . :oops:

Might have to build the engine in the frame, with the Triple .

Downdraft .


You can see here , Stock , The INTAKES have downwardly inclined , but the carbs arnt . Not that its downdraft , its just on a tilt ! .
 
Last edited:
Matt Spencer said:
Gees . You could get at least 10.000 RPM with These Things !

Downdraft .

Gurney ran these things on his PR . APPARENLY YOU HAD TO HAVE GAS IN THE TANK & THE FUEL ON , OR THEY WOULDNT WORK . :oops:

Downdraft .

Where were we , Wal ,
Downdraft .
Downdraft .
souns like there mightnt've been a lot of FUEL PRESSURE ! probly for someone who can set a Float Level .
Click to expand...
The lake injector is a nice clean design but when I tried something similar without float bowls the centrifugal force from leaning over in the turns caused the mixture to run rich and 8 cycle because the gas in the tank pushed more fuel through the carbs.
 
I probably have a jaundiced view of the world. When I was racing in the 60s and 70s, I raced a featherbed Triumph. I tried lots of different things to get it going, So when I built the Seeley 850, I was able to almost straight to what I needed. I am very sensitive to what the motor is doing when I change things. The Commando engine is extremely responsive to jetting and timing changes. When I first started racing the Seeley, I had to change three things. The single chromed disc on the front was insufficient. The standard gear ratios were hopeless, and the overall gearing was not high enough. And the motor did not perform well until I leaned the jetting off.
When I was a kid, I played with 2 into 1 exhaust systems. If there is the slightest restriction at the collector or beyond, they do not perform well. And different cam timing is needed.
I think that looking for more downdraft is futile, more valves is better. The trouble is that when you think of doing that, the problem becomes mind-boggling. What would a 750cc Paton twin be like ? The 500 is bad enough.
 
Last edited:
Of course there is one thing about insufficient downdraft, - If your tuning efforts fail, you can always blame that.
 
Status
Not open for further replies.

Similar threads

Shelby-Right
My break down fix !
2
Replies
20
Views
1,531
fiatfan
fiatfan
Supercat
Broken down in Nova Scotia
2 3 4 5 6
Replies
101
Views
5,379
Supercat
Supercat
ashman
My old British bike shop has closed down
Replies
19
Views
2,147
acotrel
acotrel
B
961 Review & South Downs Motorcycles Video
2
Replies
29
Views
3,910
brendanq
B
C
Making an oil pump for a Jawa DOHC engine
2
Replies
33
Views
2,891
Charkmandler
C
Back
Top