FA head power curve?

I have found the main jet is less important than the needle jet. I ride and tune my 850 as though it is a two-stroke. I feed the throttle on - never whack it open. If your jetting is lean right down the needle and you feed the throttle on, you do not use the main jet to get acceleration. The main jet needs to be a bit rich to stop destructive detonation, that is not the optimum for getting power. If you are on the main jet too early, you will be slower. With the close box, by the time I reach full throttle in each gear, my revs are usually high enough for the next gear change. I don't race at Phillip Island.
With the heavy crank, throttle response is very important. You don't get it if your midrange jetting is even the slightest bit too rich. And you don't get it if you whack the throttle open and rely on the main jet..
With a road bike, there are considerations other than power.

acotrel said:

I have found the main jet is less important than the needle jet. I ride and tune my 850 as though it is a two-stroke. I feed the throttle on - never whack it open. If your jetting is lean right down the needle and you feed the throttle on, you do not use the main jet to get acceleration. The main jet needs to be a bit rich to stop destructive detonation, that is not the optimum for getting power. If you are on the main jet too early, you will be slower. With the close box, by the time I reach full throttle in each gear, my revs are usually high enough for the next gear change. I don't race at Phillip Island.
With the heavy crank, throttle response is very important. You don't get it if your midrange jetting is even the slightest bit too rich. And you don't get it if you whack the throttle open and rely on the main jet..
With a road bike, there are considerations other than power.

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I agree the main jet is less important on a street bike. Especially in NZ and Oz with our tough speed laws.

But seeing videos of the USA guys riding down the road at 90 mph things might be different there.

They would be in big trouble in NZ at those speeds.

Plus main jet was an example. Needle and slide may need tuning too. I'll confess in the first year I raced my bike I relied on advice from guys around the pits on jetting. The bike ran like rubbish. Then I used the same dyno for tuning and development. I don't know if some of those guys were scamming me or what but most of the advice was miles out. I got a lot of satisfaction of beating those same guys hands down in the following years using the lessons I had learnt, including the lessons learnt on the dyno.

Tuning carburation is easy if you can think about it logically. However there are many myths. Phil Irving in tuning for speed said ' If methanol is run rich, you still get good power'. That is correct - but you do not get the best that way. Petrol is much more critical than methanol, if you get it wrong. However, in the 1950s some Australian riders raced in Europe - they found the Brits got their Manx Nortons going as fast on pool petrol as they could in Australia using methanol. Tuning a motor to go fast when using petrol and Amal carbs, is like playing cricket. It is designed to drive you insane.
if you asked anyone in the pits at one of our race circuits what you need to do, to use methanol - they would say 12 to 1 compression. .120 needle jet and 800 mains. It does not need to be anything like that.
The main reason Australian riders such as Harry Hinton Senior and Ken Cavanaugh did well in Europe was our Manx Nortons had Symco conrods and could go safely to 8000 RPM. And our riders were used to the speeds.

If I was going to ride a motorcycle on a motorway, I would make sure it was jetted too rich on the mains. It is very rare to damage a motor when it is not being run at full throttle. However, there is one thing I never do - I don't continue to run a motor which has developed a miss. I always correct it as soon as possible.

The main reason most motors are faster on methanol - it hides-up the tuning errors, But if it is jetted right - like petrol - it makes the motor much faster.
When you use a Mk 2 Amal carb, the needle jet is not a complex as those in a Mikuni carb, so you can make your own. You cannot usually drill a smaller hole in a Mikuni needle jet, after you have drilled it bigger. In some Mikuni needle jets there is a ring pressed in at the top which can be replaced. But it is pretty fiddley.
My brother has raced H1 and H2 Kawasaki two strokes on methanol in speedway sidecars for years. With a two-stroke, if you get it wrong - you pay. You cannot lower the needles and make the motor cough, to get the needle jet size correct. I had a lot of arguments with him over this. He has a jeweller friend who can actually measure the ID of the needle jets, and ream them.

johnm said:

I agree the main jet is less important on a street bike. Especially in NZ and Oz with our tough speed laws.

But seeing videos of the USA guys riding down the road at 90 mph things might be different there.

They would be in big trouble in NZ at those speeds.

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Good thing no one saw me coming home from work yesterday...

Why seek an increase in performance with a road bike anyway ? Reliability usually suffers. If I had a road-going Commando, I would keep it close to original. I might trick the gearbox, but nothing else. A Commando engine is much better with a close box. With 5 gears, it would be lovely. And that way, everything is easily reversible. - nothing is stuffed.
When I built my bike in 1978, I did not believe in the motor - I do now. The motor has had almost nothing done to it, and it is fast enough to be competitive against some very fast bikes It just needs to be used in a slightly different way - slow and steady and don't lose momentum - then it is quick.

TBH, in the UK at least, I don't think a 'road going' Commando needs or would truly benefit from a 5 speed box....

I prefer the 4 speed AMC to the 5 and 6 speed transmissions on the modern bikes.
The six speed on the Thruxton is a bit ridiculous, the bike has over 80 ft lbs from 2500 rpm to the redline.
Today's buyers think a bike has to have six gears to be worthy.
It might make sense on a peaky sportbike but its really not necessary on a road bike with a decent torque spread, and the Commando has that in spades.

Glen

The older one gets, the faster their Nortons are. They are faster than modern bikes if you do most of your riding behind a keyboard.

It is possible to build a Norton that is a reasonable performer without sacrificing reliability. Is it worth it? Not really, but it is cheaper to have a little fun and build up an old Norton you already own, than run out and buy a truly fast very reliable motorcycle.

I almost did the TTi gearbox thing, but that old AMC 4 speed is enough although a bit clunky at times. I have found that certain boots make my gearbox shift better. When I wear my stiff go fast boots I have almost no feel for the shifter. If I wear comfortable hiking boots the shifts are perfect. So maybe a compromise boot would be better than a close ratio 5 speed. I do miss the soft snick of the modern motorcycle 6 speed, but it is easier to remember what gear I'm in with a 4 speed.

EstuaryBoy said:

TBH, in the UK at least, I don't think a 'road going' Commando needs or would truly benefit from a 5 speed box....

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I have to disagree with you on that one. Most motorcycles including the Commando benefit from a five speed 'box. The smaller jump between gears gives the whole drive train an easier time. For example, when changing down for a bend, changing down to second might be a bit on the low side, but leaving it in third won't be low enough to give good pull out of the bend. But I do agree that six speeds for any engine with a reasonable amount of torque is unnecessary.

Martyn.

Ok we meet in the middle at 5

Yes, closer ratios will give a less stressful change, but I emphasise 'road going' rather than being the quickest
thing out the other side
If my engine/clutch/primary chain are suffering through my (Norton's) choice of box... so be it :-(
I haven't missed that fifth gear yet (a few neutrals, perhaps!)

worntorn said:

Ok we meet in the middle at 5

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Pub car park at 7

The last time I raced, I was using a 4 speed close ratio gear box. It was perfect everywhere except coming off the start line. I the first two corners in two races, I had guys in front of me getting in my way. In the last race, I revved the motor to about 6000 RPM and the bike jumped quickly enough that there were only 3 guys ahead of me at turn 2. I turned tighter than them and rode past the 4 of them. I was well ahead, when thefuel line came off the tap under the centre of the tank. There is a T piece there with a clip, which needs a long flat -bladed screwdriver to tighten it.
My motor stopped when I had them all cold. I DID NOT BLOODY IMAGINE IT. I had all the tight part of Winton ahead of me, and there is no way the could ever get near me going around there. They would have needed 140 BHP on the main straight, and they have not got that.
When I race I do everything slowly. I ride my Seeley 850 as though it is a two-stroke - I never whack the throttle open, because it I do that, my bike accelerates slower. I have found with the Seeley - if I gas it hard when it is on a lean, the back goes down and it turns tighter in the direction of the lean. I am on the gas, right from the start of every corner.
I do not think, I will ever have the opportunity to do that stuff again. And it really grieves me.
When I did that to Wolfenden's guys, my old mate Allan Greening and my wife were watching. My wife told me he got all excited. He is dead now - he died at the wheel of his car and it bounced off an oncoming. He did not have a mark on him and nobody else was injured - a dog in the other vehicle died. He was with me when I won a couple of races at Mount Gambier - but there was nobody there to make it really interesting.
For me, road racing is only ever about the bike - it is simply another intellectual exercise. My whole life as a scientist has been a about development of materials and processes, quality and safety.
I lost my ego, the first time I crashed in front of a crowd and looked stupid.

EstuaryBoy said:

Yes, closer ratios will give a less stressful change, but I emphasise 'road going' rather than being the quickest
thing out the other side
If my engine/clutch/primary chain are suffering through my (Norton's) choice of box... so be it :-(
I haven't missed that fifth gear yet (a few neutrals, perhaps!)

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If you have got a really well-performing road bike - how can you use it in a way which needs that performance ? When I was a kid, I had Triumph 650s going quick, and had too many near misses. So I went road-racing, where it is safer,
I am 80 and if my wife did not worry, I would race tomorrow. But I would not ride a motorcycle on public roads. When you road race, the other competitors try to avoid killing you. On public roads, other people only worry about you if you are a threat to them.
My wife has not watched many road races, so she gets anxious when there is no need. Road races look different from the outside than from within. She has no need to worry - I do not crash. I have been around too long for that. If I can still drive my car, I can certainly road race a motorcycle - it is burned into my brain.,

What is this thread about again?

In the western USA it is possible to ride a well-performing Norton road bike geared right 8/10ths through 3rd gear for a while with a 4-speed on the road where there are enough turns to make it interesting. You just have to know where you can do it without getting hit head on, or t-boned, and be willing to ring the bikes neck. Riding 10/10ths through 4th gear on the road is nuts to me though. Gotta leave some margin for error. Definitely much safer and faster racing on a track.

IOM on the road racing doesn't count. That kind of racing on the road is for a unique bread of human. Can't even imagine doing it. Fun to watch though.

I never raced road bikes on a race track, but in California the men I rode with 26 years ago did not dawdle much on the road in the open countryside or through the less populated winding mountain roads. I left the Norton at home for that stuff. It could not keep up at that pace on long rides. Then again maybe it was just me that couldn't keep up on a bone rattling old Norton with crappy brakes. lol

acotrel said:

The main reason most motors are faster on methanol - it hides-up the tuning errors, But if it is jetted right - like petrol - it makes the motor much faster.

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The reason methanol makes more power than gasoline is that at the stoichiometric A/F ratios required by each respectively, methanol has 27% more energy available.

Dan1950 said:

The reason methanol makes more power than gasoline is that at the stoichiometric A/F ratios required by each respectively, methanol has 27% more energy available.

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Methanol burns with the release of about 75% the calories which petrol does, but you use one and a half times as much methanol; The main advantage with methanol is its high latent heat of vaporisation. It cools the incoming charge which makes the air more dense - needing more methanol . It is a supercharging effect. But most guys run it miles too rich. They get slightly more power than they would get with petrol. And most of that is because methanol is more forgiving of tuning errors. To get the jetting right with methanol is actually as easy or difficult as it is with petrol.
What people do not realise is that if you run methanol lean to just before the point where it does damage , the motor becomes significantly faster. If it is jetted slightly rich, the motor will still usually be quicker than it would be with petrol. But there is a difference - run slightly rich, methanol behaves the same as petrol - just not as bad.
I think methanol works better in a Commando 850 motor than a Triumph 750 motor because of the cylinder head design, With some motors there might be a 'quench effect'. There is no squish band in a Triumph head. The crowns of !2 to 1 comp. Triumph pistons run a long way clear of the sides of the combustion chambers. And there is always coke on the side of the crown which is away from the spark plug.