Dyno tuning Amals

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Jetting methanol is the same as petrol, you just need twice the flow through the jets (1.6 times the diameter). In a kawasaki H2 or H1 two stroke on methanol the main jet is the same size as the needle jet. We recess the needle jet so the tip of the needle is trapped and meter slightly lower down. In my norton the mains are too rich, however the needles and needle jets have been carefully been made as lean as possible without getting the cough, In racing you don't get onto the mains as often as you might think. Only wankers believe that running a motor rich makes it faster either on petrol or methanol. Fastest is just before it self-destructs.
 
Useful Kawasaki toy bike info - we'll remember that the next time we are tuning our Commandos.
Not....

With miniature aero engines running methanol, you always tweak them slightly rich before launch.
That way, they come home to fight another day.

But we diverge.
Surprise, surprise....
 
acotrel said:
If you've got a four stroke jetted right, you will usually get better acceleration if you feed the throttle. Similar to riding a two stroke racer but not as dramatic. If you whack the throttle wide open, it goes straight onto the main jets which sometimes tend to cause the motor to bog down a bit. Doing that with a two stroke that can cause the motor to stop, your Norton will keep going however unless the mains are too lean it will be slower.

You need to make sure when you do your plug chops that fitting a larger main jet actually darkens the plug colour. It is possible to get the midrange jets nice and lean, however have the situation where the mains are obstructed by the needles.
Click to expand...

I'm glad people have been mentioning the short bogging that occurs when you whack the throttle wide open from a moderate rpm. After I changed the jet from 230 to 220 it was very pronounced. When the carbs recover, the bike launches like a rocket :twisted: . When the throttle is rolled on, acceleration is smooth. Lowering the jet size has given this bike better pull all the way to WOT :D . The needle clip is in the 2 slot. I should play with the needle position when I have the time.
 
If you lower the main jet size to get better response, it will probably be too lean for sustained high speed blasts, you might do damage. I'd be looking at the needle jet size and the shape of the needle. I think that a commando with Amals runs about 0.107 inch needle jets. If you lower the needles one notch from the centre and it doesn't cough when you ride it, I'd be buying 0.106 inch needle jets. The other thing which might help are Mikuni needles. In both Amals and Mikunis the needle diameter is 3mm. The Mikuni 6 range fits the medium size Amals. You need to check the distance from the centre clip groove to the shoulder. The Mikuni needles give you a far greater range of tapers. (If I want needles I usually visit my friends who have big two strokes. )
Sometimes if the mixture is a bit rich as the needle rises you might not pick the lack of performance. I know this might sound like nit-picking but you might find some gain if you play around. Record your settings and the response as you go. The jetting is far more critical with petrol than methanol. Methanol hides up the tuning errors.
 
acotrel said:
The other thing which might help are Mikuni needles. In both Amals and Mikunis the needle diameter is 3mm.
Click to expand...
The diameter of the parallel section on an Amal Mk1 Concentric needle is 0.0985" .
The parallel part of the needle stays in the needle jet up to about 3/8 throttle, and above that the taper controls the mixture.
 
Would you please measure a needle of of a larger Mikuni, I think you will find they are the same as the Mk2 Amal. The taper controls the transition from the low running jets and cutaway, to the main jet. After 3/4 throttle the mains usually control the fuel input. Getting it right at 3/4 throttle is the only difficult part of the whole process. I'm not at home or I would check the needle diameters myself, From memory there are 3 types of carb which use the same diameter needles, I think Keihin is the other.
 
Roadrash said:
acotrel said:
If you've got a four stroke jetted right, you will usually get better acceleration if you feed the throttle. Similar to riding a two stroke racer but not as dramatic. If you whack the throttle wide open, it goes straight onto the main jets which sometimes tend to cause the motor to bog down a bit. Doing that with a two stroke that can cause the motor to stop, your Norton will keep going however unless the mains are too lean it will be slower.

You need to make sure when you do your plug chops that fitting a larger main jet actually darkens the plug colour. It is possible to get the midrange jets nice and lean, however have the situation where the mains are obstructed by the needles.
Click to expand...

I'm glad people have been mentioning the short bogging that occurs when you whack the throttle wide open from a moderate rpm. After I changed the jet from 230 to 220 it was very pronounced. When the carbs recover, the bike launches like a rocket :twisted: . When the throttle is rolled on, acceleration is smooth. Lowering the jet size has given this bike better pull all the way to WOT :D . The needle clip is in the 2 slot. I should play with the needle position when I have the time.
Click to expand...

This,.... is why CV carbs were used on newer bikes. They open the slide only as fast as the engine's vacuum can stay up.
 
I only use plug readings to set the main jets. Many people don't know how to read a plug, they simply look at the electrodes and surrounds. You need to look right down inside where the porcelain joins the metal. If jetting, timing, fuel type, plug heat range and comp ratio are correct, there should be a 2mm black ring there. If you are racing, the black ring just disappears. I only learned this from a lecture by Barry Smith the Derbi rider in the 60s.
 
True all that. But I do. And it's worth learning how IMHO. I've found that owning a Norton is just one big learning curve. But now I get dozens of worry free miles LOL. :mrgreen:
 
Why not just pop an O2 sensor bung into a hidden location somewhere in the exhaust, then tune the carbs to perfection without guesswork?
Glen
 
worntorn said:
Why not just pop an O2 sensor bung into a hidden location somewhere in the exhaust, then tune the carbs to perfection without guesswork?
Glen
Click to expand...

Interesting, How does that work?
 
Weld in a bung, screw in the sensor, connect and temporarily mount the controller ,then ride the bike and take note of readings. Make jetting changes based on readings. A reading of somewhere very close to 14.3 is perfect for cruising and right around 12.5 when hard on the throttle pulling a hill is ideal. High readings are too lean and can cause piston holing, low readings are too rich, cause power loss and high fuel consumption.
The sensor system I am describing is the most modern type which uses a wideband heated sensor, power for that comes thru the controller. Older types used narrow band unheated sensors. The advantages of the heated wide band type are that they give much more accurate information than the unheated narrow band plus the sensor can be mounted quite far away from the head, ie tucked in on the lower inside face of the horizontal portion of the header somewhere.
Unheated types must sit very close to the head, so the bungs are front and centre, not pretty.
Once tuning is done, a flush plug goes in the bung.
If a different type of Carb is used on the bike at a later date, out comes the plug and in goes the sensor for tuning.

Glen
 
baz said:
changing your main jets wont affect your acceleration you need to make sure you have all the settings right IE the pilot air adjustment the right size cutaway slide needle position the main jets have very little effect at the lower end also a lot is dependent on engine condition ,good compression etc if you get the chance "ride someone elses commando just for a comparison" ,,,,,,,,,,,,,,,,baz
Click to expand...

"ride someone elses commando just for a comparison"
I like that idea, also I like for them to ride mine so as to get their opinion.Though there are a few Norton owners around here,
it's hard to find any that actually "ride" a Norton often enough to have a feel for them. Mine stays on the road. And using my own twisted logic is why I believe she is still alive and kicking.

Cheers
 
Well, so many opinions written with such conviction :wink: What started this for me is conflicting information for initial carb setup. The shop manual shows a 230 main, #2 clip slot for the combat. Amal sold me a set of carbs specifically for the 72 combat heads I'm using, which came with 220 jets, #2clip slot. I put the 230's in believing Amal had made a mistake. Then I came across this info sheet here recently amalcarb-info.php, listing 220 jets, #1 clip slot for a 72 combat. So I put the 220's back in.

Even published information has different opinions :roll: I guess the answer to my original question of "is it worth dyno tuning Amals" is yes if you are a stickler for perfect, no if the bike runs good enough for you.

I'll probably end up getting it dyno tuned cause I'll always wonder.
 
If you are a stickler for perfection,use an O2 sensor, not a Dyno. A Dyno can get you there eventually, but compared to the sensor it is like groping around in the dark vs bright sunshine.

Glen
 
I spent my whole working life as an industrial chemist and I'm always suspicious of black boxes especially when they are in the hands of engineers. If you use an oxygen sensor, how do you know specifically what it is measuring and what the response time is ? There is an old saying 'what gets measured gets managed', however it does not matter good an oxygen sensor might look in theory what you see is not necessarily always what you get. My approach is to ride the bike many laps of a race circuit and count the gear changes, you usually know if you are getting there quicker. The straights get shorter and the bike gets harder to stop.
 
acotrel said:
My approach is to ride the bike many laps of a race circuit and count the gear changes, you usually know if you are getting there quicker. The straights get shorter and the bike gets harder to stop.
Click to expand...

So does your RACE in/experience with METHANOL count for anything when tuning a ROAD bike for PETROL. ??

As has been pointed out previously, many times, methanol is very forgiving as far as tuning goes.
It can be 50% too rich, according to no less an authority than Phil irving, and still work OK.
Without that O2 probe, you wouldn't know...
 
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