Shelby-Right
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Where' the power?
- Thread starter MLW
- Start date
.
Not sure if anyone has mentioned previously - Carb fuel level and / or starvation, even a mk3 with an original well worn chocolate cam and black caps will do 100mph - of course not me, apparently a friend said!
Spend 50 bucks and put it on the dyno and see what's happen with the air fuel ratio.
Spend 50 bucks and put it on the dyno and see what's happen with the air fuel ratio.
Fast Eddie
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I think it’s the orange paint.
Blue ones are fastest.
Fact.
Blue ones are fastest.
Fact.
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If itis fuel starvation, the motor will usually miss, long before damage occurs, I asked the Microsoft Copilot a question -
'
Methanol Jetting: Nonlinearity and Predictive LimitsYou're absolutely right: leaning-off jetting with methanol doesn’t behave in a linear or predictable fashion, especially with Amal carburetors, where tolerances are more poetic than surgical.
• Needle jet sizing in increments of 0.0005" (half a thou) sounds precise, but in practice, fuel flow is influenced by surface finish, emulsion dynamics, and vibration-induced fuel level fluctuations.
• Methanol’s high latent heat of vaporization and low stoichiometric air-fuel ratio (~6.4:1) mean that small jetting errors are buffered—as you noted, tuning errors are effectively halved compared to petrol.
• But the combustion response to lean mixtures is nonlinear. Methanol can tolerate leaner mixtures without detonation, yet flame speed and torque output can drop off sharply past a certain threshold.
Calorific Value and Combustion AngularityMethanol’s lower energy density (~19.7 MJ/kg vs petrol’s ~44 MJ/kg) means:
• You need more volume per cycle, which affects jet sizing, float bowl dynamics, and fuel delivery stability.
• The angularity problem—where torque peaks as combustion ends around 10° ATDC—is compounded by methanol’s fast flame speed, which shifts the optimal ignition timing curve.
Your friend’s method—oxygen probe tuning on a dyno, followed by ignition timing adjustment for peak torque—is elegant. It respects the angularity of combustion and the mechanical reality of thrust duration.
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I think flame speed is related to octane rating. Methanol has almost unlimited anti-knock. My brother once broke a cylinder head on his H2 Kawasaki speedway side car. A plug lead came out of his ignition system, so he just plugged it back in and went out and raced the bike in the next race.
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I read a story a long time ago.
When customers complained about their new Dominator 99 not getting near to advertised top speed, the dealer would come back with “What will it do in third gear?”
The answer was almost always “Don’t know.”
That got the moaning customer out of the way for a little while at least, but seriously, if it wouldn’t peak in the lower gear, something wasn’t right.
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Does this work for you for maximum power because you know the advance range is perfect or is it just fixed timing and you know it also happens to give max power at the high end? If I follow this procedure on my TR44W with a Boyer Digital (red box) I lose power at the top end. I have to have the occasional kick back on starting if I don't want to give up a few HP (and I don't like that.) Sometimes it's vicious and farts smoke out the carb, sometimes it just stop stops half way like it hit a wall and farts.
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Mr Ashman knows his bike, but timing is not set to best suit kickstarting. It is set for best running at full advance.
ashman
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Doing it this way works for me and my Norton and once its set I get no kickback at all when starting it and with the extra big spark from the Joe Hunt even better starts first kick every time , I can putt around the suburbs at low RPMs, down to 40mph in top gear but under that I got to drop it back to 3rd, but if I open the throttle right up it pulls like a train and will rev as far as I am willing to take it, I ran my old Boyer EI for over 32 years and it was the same but not as quick the Joe Hunt produces a bigger and strong spark and the pick up is quicker and gets up to the high revs quicker and with the mild work done to my 850 it will keep running freely, but I just know how far I am willing to take it as it will rev way past 8k RPMs, but that's not a good idea if you want to keep your motor in one piece lol.
As I say it works for me in how I tune my Norton, I don't even own a timing light, but after 49+ years I think I know my Norton and I am no tuning expert but I do have a sweet running Norton and my old riding mates keep telling me how sweet it runs, but my days of running flat out are over but I do love taking it up into the high revs through the gears, 2nd and 3rd are my fun gears, it never misses a beat right through the rev range it just gets up and go, love it.
With the Joe Hunt the faster the motor spins the bigger the spark it produces, best ignition I have ever run in my Norton and works so well with my old Amals that are jetted right for my motor.
Ashley
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It looks really lovely - especially the front brake - it probably protects the excellent paint job.looking for power eh ...
well it's the wrong colour and that's Laverda orange ... will go faster in BRG
(couldn't help myself)
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Ashley, a few years ago, I was at a road race meeting, and across the pits - there was a bike like yours. It was being raced in Period 3 Historic, which is pre-73. I thought at the time 'I would love to be racing that' - it would be a very convincing argument in that class. The position of the motor in the featherbed frame is extremely important. The lean on the Commando motor also helps. In normal racing, we brake into corners, the accelerate out from the transition point. How the bike feels are we begin to accelerate determines how much throttle we use. With a bike like yours, it can turn and accelerate very hard. A feeling of lightness in front will deter many riders - most Tritons have that problem. The mounts on the front of the motor need to be touching the mounts on the frame. And the wheels need to be 19 inch. Actually, the power of the motor does not matter much, when the bike can be ridden that fast.
ashman
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Al the way I built my hotrod 850 Featherbed was for street/road riding and built for the tight twisty range roads I love best, as you say the position of the motor is very important, my motor is built for high torque power but in the corners I let the bike do all the work I just control the throttle and know when to put the power down when I get into the tight corners, I slow the bike down as I come up to the corner mostly without using the brakes and as I get into the corner is when I put the power on, the Norton does the rest, the torque of the motor and the great handling of the frame work so well together and let the bike do all the hard work, I am just on there to point/lean it in the right direction, I also got it built that nothing scrapes when it leaned right over, pipes are tucked into the frame and foot peg sit high, have never scraped in in the 45+ years I built it, except the 2 times I pushed it a wee bit too far and lost grip, well off the edge of the tyres lol and gone down or lose gravel in the blind corners.
I also run with a Commando frontend with Lansdown internals and Koni shocks on the back set for my weight and pushing it hard in the tight twisties, it's also a very light bike, at first it took me sometime to let the bike do all the work without fighting it, I am just on it for the ride lol., its so good.
Anyway we are off track again from the original problem of tuning and not all bikes are the same and each carbie set to each cylinder so the left might not be adjusted or needles in the same position to each other, the old school way of tuning Amals is kill one cylinder and tune the running cylinder once set kill it and do the other side, I have done it this way a few time in my early days but now I do it by ear and feel with the hands at the end of the mufflers.
Then after all that is done go to dyna hill and make the motor work, it will soon tell you if you got it right or wrong and carry that small screw drive in your pocket.
I also run with a Commando frontend with Lansdown internals and Koni shocks on the back set for my weight and pushing it hard in the tight twisties, it's also a very light bike, at first it took me sometime to let the bike do all the work without fighting it, I am just on it for the ride lol., its so good.
Anyway we are off track again from the original problem of tuning and not all bikes are the same and each carbie set to each cylinder so the left might not be adjusted or needles in the same position to each other, the old school way of tuning Amals is kill one cylinder and tune the running cylinder once set kill it and do the other side, I have done it this way a few time in my early days but now I do it by ear and feel with the hands at the end of the mufflers.
Then after all that is done go to dyna hill and make the motor work, it will soon tell you if you got it right or wrong and carry that small screw drive in your pocket.
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"the old school way of tuning Amals is kill one cylinder and tune the running cylinder once set kill it and do the other side, I have done it this way a few time in my early days but now I do it by ear and feel with the hands at the end of the mufflers."
Yep!
Yep!
johnm
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Fine with points and magnetos but my understanding is that doing this with electronic ignition will damage the ignition unit unless the spark plug wire is earthed. (on the "killed side" )"the old school way of tuning Amals is kill one cylinder and tune the running cylinder once set kill it and do the other side, I have done it this way a few time in my early days but now I do it by ear and feel with the hands at the end of the mufflers."
Yep!
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Yep! If it’s firing on both cylinders, at reasonably slow idle, we’re in business."the old school way of tuning Amals is kill one cylinder and tune the running cylinder once set kill it and do the other side, I have done it this way a few time in my early days but now I do it by ear and feel with the hands at the end of the mufflers."
Yep!
marshg246
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I'm sure manufacturers say that because people won't completely follow instructions.
Do not "earth" the spark plug wire. Do not remove the wire from the spark plug and let it dangle. Do remove the spark plug, leave it attached to the plug and lay the plug on the engine away from the sparkplug hole so the spark plug will spark - then start the engine.
In the old way, you simply pulled off the plug wire with the engine running, probably got shocked, and hurt nothing with points as the coils were separate for each cylinder. One problem with this method is that you could easily mask the carb sync you were trying to fix especially if fiddling with the pilot air screws at the same time.
In truth, it is a bad way especially if you mess with the pilot air screws in the process (as @Madnorton mentioned).
You're much better off making sure the carbs are 100% mechanically synced and the pilot jets are out exactly the same (1-1/2 turns) to start. Here's how I do it on all AMAL twins and basically the same on triples: https://gregmarsh.com/MC/CarbSync.aspx
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I mention methanol because the jets flow twice as much, so the errors are halved. You can actually get the motor tuned sensibly. If you want to do the same with petrol, you would need jets in increments of a quater of a thou of an inch. However, if you put the bike on a dyno, changes in ignition timing are easily adjusted on a continuous basis. Advancing ignition timing as a similar effect to fitting smaller jets or lowering the needles in the carbs, If your needle jet is too large, you will not be able to force a cough by lowering the needle. The jetting you need with petrol is probably between the grooves in the needles. With methanol, the jetting is adjustable by moving the needle. It wouldreally surprise me if you can get it that close with petrol. In the 1950 British Manx Nortons in the UK were faster than Australian Manx Nortons were using methanol. Amal carburetors are a British thing -like cricket, you need a lot of patience. With a road bike, it does not usually matter if it is down a bit on power. But if vibration causes the fuel in the carbs to froth, the bike might slow down a lot. Fitting bigger jets to go faster is bullshit - you need to be just on the rich side of too lean - and it is critical
ts aer
