Carb balancing

[crossthread]

Is it practical to drain each float bowl separately, compare the volume in each carb, and then determine float height balance ? This would appear to be an accurate way of measurement , especially if you knew that one particular carb was set exactly right. Any thoughts / comments ? May be people do this anyway and it's passed me by (like a lot of things )

[warren3200gt]

That would work IF all the floats had exactly the same buoyancy.

[Ultim8pc]

To set them properly you need to remove thee carbs, measure/set the float heights and check the fuel heights and adjust accordingly to get the correct fuel height.

[ZedHead]

That would work IF all the floats had exactly the same buoyancy.

Clever bloke that Archimedes chappy

[warren3200gt]

That would work IF all the floats had exactly the same buoyancy.

Clever bloke that Archimedes chappy

New a thing or two about screwing apparently too!

[ZedHead]

That would work IF all the floats had exactly the same buoyancy.

Clever bloke that Archimedes chappy

New a thing or two about screwing apparently too!

[crossthread]

Okaaaaay . But when you set the fuel level you don't take float buoyancy into consideration . You measure fuel height against the float bowl , presuming that the float bowls have equal volume then you are measuring the volume of fuel , which should be consistent across the carbs . Volume is a much more accurate measurement than eyeing up the height of fuel in a plastic pipe. To equalise the volume you bend the float tang as per normal . What am I missing?

[warren3200gt]

Lets say one float was light and one was heavy. The light one would displace less fuel to float. If it was set at say 3 mm below the bowl flat and measured say 100ml liquid volume.
The heavy one would displace more fuel to float . At 3mm below the bowl flat and would only measure say 90ml liquid volume.
Soooo, if you set them all to 100ml then the actual fuel level below the flat in the bowl would be different in every carb. Consequently it would be easier fot the "high level" carb to pick up fuel through the pilot/main than it would for the "low level" carb.
So if they are all set to 3mm below the bowl flat using the wet method then the the float buoyancy is irrelevevant and all the carbs feed fuel equally.

[Ultim8pc]

What am I missing?

Nothing, except you're over thinking it in my opinion...
Measuring works.

[ADRIAN H]

Virtually impossible to measure volume of carb float bowl.

Recommended method of setting up carbs is bench set them with 0.6 - 0.7 mm gap between cut-out to front face of the slide and base of the throat (inlet slide).
With air screws set to recommended settings for bike, (which varies across the range).

[crossthread]

YAY. IV'E GOT IT . Thanks warren3200gt , good explanation. Of course , the volume in each float bowl will be different because each float will have a different displacement. I know the recommended way to do it , done it many times . I was trying to re-invent the wheel . I gotta disagree with Adrian H though , draining each carb in turn and measuring the volume of the fuel would be easy , and you gotta drain the carb to fit the measuring pipe. Over thinking ? me ?

[warren3200gt]

[Al]

The first float bowl you empty will be the bowl plus the fuel in the hose above it. Subsequent ones no so much, but not impossible to replicate. On mine it would measure the bowl in question plus part of the others as well, as each bowl is linked at the bottom for the accelerator pump. I also have two fuel feeds with filters which either do or dont empty depending on their mood. For these reasons and the fact that you cant measure volume of the bowls as an indication of fuel level whilst its running, i will personally stay with a bit of plastic tube. As a matter of interest; fuel volume is also not an indication of re-charge rate and for reasons too boring to mention i have had hours and hours of grief very recently on the subject of re-charge rates which caused me to drop a valve as it was too slow in just one carb!

AL

[johny brando]

Is it practical to drain each float bowl separately, compare the volume in each carb, and then determine float height balance ? This would appear to be an accurate way of measurement , especially if you knew that one particular carb was set exactly right. Any thoughts / comments ? May be people do this anyway and it's passed me by (like a lot of things )

Hi Crossthread......Sorry but your theory is not practical & it will not work effectively ! The factory worked it out just fine " as they usually did 99.5 % of the time" They understood & accepted Bernoullis Principle that is applying at that point within the carburettors and how it affects the needs & requirement in relation to a constant fuel /air mixing .....therefor the needed requirement of having a " Set Datum point " by using their own given FUEL LEVEL HEIGHT measuring point method, in conjunction with using the correct gauging and setting method via the clear pipe...... this is the ONLY true, easiest , uncomplicated accurate method to do it....that said a wider segment at the upper measuring end of the tube is beneficial to negate the surface tension error occurring at the internal liquid / tube wall interface point i.e. the point where your taking /measuring off your reading ..... Now my Brain hurts ! haha.
Cheers Johny. B

[ADRIAN H]

I gotta disagree with Adrian H though , draining each carb in turn and measuring the volume of the fuel would be easy ?

Float bowl fuel volume can’t be measured by measuring the volume drained out - as fuel will still be in fuel lines and also in the fuel lines between pairs of carbs.