Dyno tuning Amals

Roadrash · Jul 16, 2014

Should I spend the money on dyno tuning my bike if it already runs well? My combination of parts is not stock and I'm always wondering if I might be leaving some power on the table from over-carburation . The acceleration is not impressive to me, but I came from 120 hp race replicas.
1971 750 cylinders and bottom end
72 combat heads
stock cam
twin new 32mm Amals, jetted per the shop manual for the combat. 230 main jet.
Think I should just try the stock 220 jets and see if acceleration improves?

baz · Jul 16, 2014

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

concours · Jul 16, 2014

"changing your main jets wont affect your acceleration"

It certainly will. :idea:

OP,
I like to tune going a bit too far rich, then leaner. YMMV

baz · Jul 16, 2014

ok maybe i should have said unless you are opening the throttle more than 3/4 when you accelerate i doubt going down from 230 to 220 will help but try it and see but also check you have the other settings right ,,,,,,,,,,,,,baz

Rohan · Jul 16, 2014

You are doing a pretty fair rate of knots by the time the main jet(s) come into play.
Try dropping the needle a notch ?
But watch for signs of overheating - blued pipes etc.

Combat head without the combat cam is a slightly offbeat combination,
obviously, won't give true Combat performance...
You don't say what mufflers or aircleaners this is with either - peashooters ?

1up3down · Jul 16, 2014

Should I spend the money on dyno tuning my bike if it already runs well?

No

auldblue · Jul 16, 2014

1up3down said:
Should I spend the money on dyno tuning my bike if it already runs well?

Click to expand...

No

Why not? After all it's a good day out , a bit of banter with the boys , if it shows the set up is good it's a confidence boost on your commando abilities . If not , you get your bike running better . Win win for me!

J

pete.v · Jul 16, 2014

Rohan said:
Combat head without the combat cam is a slightly offbeat combination,
obviously, won't give true Combat performance...

Maybe not, but it sure didn't hurt.
The stock cam is no slouch with some bolt ons such as 32mm amals, bigbore exhaust and a combat head.

Roadrash · Jul 16, 2014

I've canceled my dyno appointment. Although i'm curious what the data might be I believe I still have some futzing around with tuning guides and different combinations before I pay the bucks for shop time.
I took out the 230 jets put a set of 220 in for a run. The bike is deffinetly a bit snappier at WOT. A plug chop and inspection showed no color at all, clean at the tips. Before they were tan on the tips, black at the threads. I'll keep an eye on them for signs of too much heat. I should probably raise the needle position to the top slot and see what that dose.

Thanks for your input gents

auldblue · Jul 16, 2014

Road rash
What plugs are you running? Have you experimented?

1up3down · Jul 16, 2014

Before they were tan on the tips, black at the threads.

It used to be that reading air/fuel mixture was as easy as what you have done

but everything source I read nowadays says nope, no good, that because of modern gasoline the only correct way to read mixture is way deep inside at the base of the ceramic insulator and they say one should have a magnifying glass and a strong little light

auldblue · Jul 16, 2014

1up3down said:
Before they were tan on the tips, black at the threads.

Click to expand...

It used to be that reading air/fuel mixture was as easy as what you have done

but everything source I read nowadays says nope, no good, that because of modern gasoline the only correct way to read mixture is way deep inside at the base of the ceramic insulator and they say one should have a magnifying glass and a strong little light

I spoke to the green spark plug co guy and he did say old plugs were better because they stood contamination better , plugs nowadays are made for computer regulated engines not old style motors.

J

ILLF8ED · Jul 17, 2014

Combat head without the combat cam is a slightly offbeat combination,
obviously, won't give true Combat performance...
You don't say what mufflers or aircleaners this is with either - peashooters ?[/quote]

Having rectified combat engine with standard camshaft last season, I can report much better performance with the combat cam and much reduced pinging with current fuel.

auldblue · Jul 17, 2014

illf8ed said:
Combat head without the combat cam is a slightly offbeat combination,
obviously, won't give true Combat performance...
You don't say what mufflers or aircleaners this is with either - peashooters ?

Having rectified combat engine with standard camshaft last season, I can report much better performance with the combat cam and much reduced pinging with current fuel.[/quote]

What did you do to the pushrods ref length , type?

Cheers j

Roadrash · Jul 17, 2014

quote]

Having rectified combat engine with standard camshaft last season, I can report much better performance with the combat cam and much reduced pinging with current fuel.[/quote]

Then I'll have to try a hotter cam next build. Luckily, I'm not experiencing any pinging with the stock cam.

Roadrash · Jul 17, 2014

Rohan said:
You don't say what mufflers or aircleaners this is with either - peashooters ?

K&N filter replacement for the stock ham can, straight through pea shooters silencers.

acotrel · Jul 18, 2014

Rohan said:
You are doing a pretty fair rate of knots by the time the main jet(s) come into play.
Try dropping the needle a notch ?
But watch for signs of overheating - blued pipes etc.

Combat head without the combat cam is a slightly offbeat combination,
obviously, won't give true Combat performance...
You don't say what mufflers or aircleaners this is with either - peashooters ?

Regardless of revs or speed of the bike, if the throttle is wide open the motor is usually running on the main jets. You need to get the midrange jetting right - as lean as possible right down the needle without getting a cough, using fairly rich main jets. Then lean off the main jets by doing high speed plug chops on a slightly uphill piece of road. If the mid range jets are very lean, the motor will spin up at its quickest as you open the throttle. Then the main jets are not so important as long as they are not so lean as to cause burning of pistons and valves during the occasions when you are really fanging the bike.

acotrel · Jul 18, 2014

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.

Rohan · Jul 18, 2014

If you whack the throttle wide open at low speeds, the vacuum is so low that the main jet doesn't feed anything like its full capacity.

I've heard of carbs where the main jet had fallen out or wasn't even fitted,
and except at a fair rate of knots, it doesn't even show.
Someone reportedly rode their bike - sedately - for years without main jets fitted.
Haven't tried it myself though.
And we know you haven't ridden a road bike for 40 years - or a Commando on petrol either !

Would agree with you about feeding the throttle in incrementally though.

auldblue · Jul 18, 2014

Rohan said:
If you whack the throttle wide open at low speeds, the vacuum is so low that the main jet doesn't feed anything like its full capacity.

I've heard of carbs where the main jet had fallen out or wasn't even fitted,
and except at a fair rate of knots, it doesn't even show.
Someone reportedly rode their bike - sedately - for years without main jets fitted.
Haven't tried it myself though.
And we know you haven't ridden a road bike for 40 years - or a Commando on petrol either !

Would agree with you about feeding the throttle in incrementally though.

Would that be true for methanol also, re no main jet?
J

Dyno tuning Amals

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