Dumb question time: why does having the floats too high cause rich running?

Ventodue

Ventodue

Hero member
Location
France
All in the title really ... :)

Can someone please explain to this simple soul just WHY having too much fuel in the float bowl makes for a rich mix?

I have a note from Piet that says, "The float height determines the fuel level in the emulsion tube". OK .... So does that mean that having too much fuel in the float bowl causes some of it to feed in thru the atomiser/emulsion tube when only the idle circuit should be in play?

Or what?

TIA for all clarifications.Principal parts diagram from manual.jpg
 
Yes.
Too much fuel = too rich.
I should imagine that fuel needs to be sucked up into the emulsion tube by the venturi induced depression, not pushed up by too high a fuel level.

Paul
 
If you think of blowing hard across the open top of a tube with fluid at a set level in it. The closer the fluid is to the opening at the top of the tube the easier it will be for the fluid to be sucked out of the tube. With a float system to keep the fluid level at a given height you can see how float height works.
 
or with the float set too high, its easier for the motor to such the fuel, so it gets too much.
CLEM
 
'fanks peeps. So it's no more complicated than the depression in the venturi sucking excess gas out of the atomiser?

"In inviscid fluid dynamics, an incompressible fluid's velocity must increase as it passes through a constriction in accord with the principle of mass continuity, while its static pressure must decrease in accord with the principle of conservation of mechanical energy (Bernoulli's principle). Thus, any gain in kinetic energy a fluid may attain by its increased velocity through a constriction is balanced by a drop in pressure."

(Errr, wot? Say that again, please, but more slowly ...)
 
Craig,

Too much fuel causing a rich mixture is pretty obvious, but the other extreme is a lot more hazardous and causes far more damage.

A too low float can lower fuel level to the point that the vacuum in the mixing chamber during cranking isn't sufficient to draw fuel upwards for starting. Correct float height influences fuel delivery through the entire rev range and sort of provides a base line for all other adjustments.

Keep an eye on the float heights especially on your 120, these are notorious for slowly deteriorating performance (but hardly noticable!) through lean mixture and then burning either a piston or a valve due to float valve wear.

piet
 
Yes to sfcpiet. Possibly a combination of both. My SFC1000 seemed to run ok until called on on in the higher registers. Slowly but surely it was losing it. No3 was flooding and adjusted for it but getting all 3 carb floats as close as possible to balanced was a huge improvement on performance. No 2 was definitely low.

Still, one can "fettle" constantly but +30 year dellortos need cleaning up, kits through them and set up properly.

Or switch to Mikunis :D
 
Schurminater said:
Interesting question and informative answers for something we've maybe always / never though about but now we know (y):cool:
Click to expand...
It was inspired by someone on a Ducrappi Forum with a rich-running single.

While it was easy to say, 'Make sure the float height is right' - and, most importantly, to do so the way Dell'Orto tell you ... ;) - I was aware I didn't actually know WHY it was ..
 
Last edited:
You must log in or register to reply here.
Back
Top