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There is always a manufacturers' spec. for float height. I suggest you set them at that, and jet to that. Leaning off your carburation by lowering the float height is not a good way to go. There are a couple of things to also consider - the tank breather might be blocked, so flow of fuel into the carbs might be erratic. Also it pays to check that the float needles and seats are all hunky-dory - no obstructions or sticking, and the tips are not worn.
 
Holding the ticklers to depress the float, raises the fuel level to flood fuel through the jets - sure.
Too high a float level will give a rich fuel mixture by flooding through the jets. This too I understand.
Lowering float level will lean the fuel mixture - How is that possible? unless the main jet and pilot circuit are uncovered (i.e. float bowl is almost empty) the jets will meter the correct volume of fuel for their orifice / setting according to the vacuum draw.
Tubes / bell mouths aim to reduce air turbulence into and across the venturi to draw fuel more consistently and give a better cylinder fill with a homogeneous air:fuel mixture.
Ta.
 
Pressure on the jet is related to fuel depth. Lowering the level reduces the pressure. The flows through the jets are very sensitive to pressure changes. It is better to set the level at a fixed point then jet to it. Within reason it doesn't matter if the level is high or low when you adjust the jetting it will be OK, as long as the level is fairly constant and the same on both carbs - makes the tuning task easier. The manufacturers' specs for fuel level, should be adhered to . Pick a point and keep to it. It is not so bad on old four stroke clunkers, however a two stroke on methanol is something else. They get expensive very quickly.
 
acotrel said:
Pressure on the jet is related to fuel depth. Lowering the level reduces the pressure. The flows through the jets are very sensitive to pressure changes. It is better to set the level at a fixed point then jet to it. Within reason it doesn't matter if the level is high or low when you adjust the jetting it will be OK, as long as the level is fairly constant and the same on both carbs - makes the tuning task easier. The manufacturers' specs for fuel level, should be adhered to . Pick a point and keep to it. It is not so bad on old four stroke clunkers, however a two stroke on methanol is something else. They get expensive very quickly.
Click to expand...

1. Commando thread.
2. Your statement re "Pressure on the jet..." means Bernoulli's life work was in vain and has been supplanted by Acotrel's Assertion. Without pushing down on the ticklers, why doesn't the "pressure on the jet..." push fuel through the jet when the bike is not running?
Ta.
 
.25" is in spec just at the lower point of the range. Also, where to measure on a Commando with the tilted carb. Both sides now match and the right appears fine, though slightly rich. Will keep an eye on the left had plug for a while.
 
needing said:
Lowering float level will lean the fuel mixture - How is that possible?
Click to expand...

https://www.oldbritts.com/amal_tun.html

The actual specification, from the engineer who designed the Concentric Barry Johnston, gives a gas level of between .170" to .240" below the top edge of the float bow, 170” being rich and .240" being lean. This level has a dramatic effect on the running of a properly tuned motorcycle. It pays testaments to the design of this carburetor that the range of miss-adjustment it can tolerate and still have the motorcycle run, if only poorly. It is suggested that you set the float level first before doing any carb adjustment.
Click to expand...
 
Float level measurement is with bowl on bench.
Height adjustment is via float needle seat movement not tang bending.
Are the compression ratios, throttle slide movements and vacuums equal?
Ta.
 
Goodo LAB
"...and .240" being lean...". How??
Reading it and roting it does not explain it.
Ta.
 
needing said:
Goodo LAB
"...and .240" being lean...". How??
Click to expand...


http://www.mikuni.com/pdf/vmmanual.pdf
Plug pics
 
blaisestation said:
On the stay up floats you can bend a Tang !!
Click to expand...

"...can.."
Sure you can, but "...float needle seat movement..." is the correct way 'cos it can't bend back.
Ta.
 
Hi LAB.
Talking AMALs here.
You still have not explained - how? perhaps why?
Ta.
 
needing said:
blaisestation said:
On the stay up floats you can bend a Tang !!
Click to expand...

"...can.."
Sure you can, but "...float needle seat movement..." is the correct way 'cos it can't bend back.
Ta.
Click to expand...

It is the correct way to adjust a 'Stay Up' float: http://amalcarb.co.uk/optimising-mark-1 ... uel-levels

The new Amal "Stay Up" float has stainless steel tangs which can be bent to alter the fuel level. The tangs can be easily adjusted by clamping the float in a vice up to the spindle hooks and tapping the body of the float gently in the direction required until the required level is achieved.
Click to expand...

The Stay Up tangs certainly don't 'bend back'.
 
needing said:
Hi LAB.
Talking AMALs here.
You still have not explained - how? perhaps why?
Click to expand...

Amal, Mikuni makes no difference.

Plug pics


Obvious common sense and is what happens when you lower float height, in my opinion.
 
Hi again LAB
I am corrected re float tang. Ta. Hi blaisestation, you are correct too.
Float level - I remain agnostic due to rational explanation dearth.
Common sense = conventional wisdom = rote learnt = unquestioning.
Ta.
 
Conventional wisdom repeated ad nauseum is dogma/mantra not rational thinking.
I'm out of this thread until it goes somewhere.
Trials with EGT and AFR sensing 5mm, 10mm, 15mm? below bowl lip now on the agenda.
Ta.
 
htown16,
I still think the white plug looks fine. Color is not as good an indicator with unleaded 10% ethanol gas these days. As long as the plug does not look damaged, evidence of boiling of the porcelain which shows up as black specks, melted or eroded side strap and center electrode, or balls of aluminum on the porcelain, I'd actually try to get the dark plug to match.

Also, it's damn hard to get a comprehensive read from just a couple of photos.

And just one thing else, now that you've painstakingly set the float levels to be equal and both carburetors are running the same parts with identical needle positions, you could try switching the jet holders complete or just the needle jets. See if the plug colors follow those parts. And if you've got a micrometer see how identical the metering needles really are.
 
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