ET: Engine (Twin) 276 Carb Float Levels

[Speedtwin]

Following on on Carls question.
I have recently over hauled my carbs on the Rapide.
I have dropped my needle on notch as was a bit rich and raised my float height one notch.
I was suffering from fuel starvation at speeds above 70 mph felt like I was emptying the float bowls.
When I last over hauled the carbs I set the float levels to the lower setting both front and back.
This is when the restriction was felt I stuck with it.
Hence I have raised the floats one notch.
I have set the bowls front as far forward as I can and it sits level.
I have set the rear as far back as I can and again is fairly level.

My question is if the float level is low what is the effect?
My system flows well both taps open is unrestricted and clean as a whistle.

 

[Vincent Brake]

what I would set floatlevel at is middle or bit under the air screw Al.
if low than lean to very lean mixture. (nearly cost me a Piston on my A single)

 

[LoneStar]

raised my float height one notch

What sort of carb / float / float needle are you running?

The float needle on an original Amal 276/289 carb has no provision for varying float height. In recent times Amal has sold a plastic float, on which they failed to match the buoyancy specification of the original brass one, and compensated with a second notch on the float needle for use with these.

 

[Cyborg]

Gas cap vent? Maybe flow is ok initially, but drops when the vent can’t keep up with the fuel flow? Will it run ok for a while before the problem occurs?

 

[Speedtwin]

279 carbs with the amal white plastic float with two notch's, notch one float low was quite low have moved up to notch two level up by 6mm.
Venting is good at cap.
I had thought the level to low so lean although had bike set up quite rich as I was in the getting to know you period.

 

[vibrac]

As has been said recently a clip fitting 276 can be rotated on the inlet spigot to vary the effective float height
the two notches on the float spindle is for copper or plastic floats
with sadness now Esso supreem is joining E5 I shall be getting 4 or 5 poison proof plastic floats this winter.

 

[Speedtwin]

Good job, seeing some remarkable ethanol damage on old parts this season on some of the pre war stuff.

 

[LoneStar]

now Esso supreem is joining E5 I shall be getting 4 or 5 poison proof plastic floats this winter.

What problem does ethanol pose for the original brass floats? Here we're stuck with E10 at the pump, have been for decades, and I've had no issues in this area.

 

[oexing]

As to brass floats I would not think they could be attacked by ethanol fuel. BUT it seems very old floats made from brass - and other parts in brass - can develop cracks in time, even when sitting on the shelf. That happened with my R 69S Bing carbs a few years ago in short time when at least two floats failed on the road. In the photos when you zoom in you can see cracks, one was soldered for quick temporary repair.
These Bing floats are very thin walled, only 7 grams . Sure, new production Bing brass spares are € 50.- each but you won´t be surprised I went the full Monty and fabricated a pair from Stainless, even lower weight of under 4 grams. Stupid me, I picked sort of springsteel stainless foil, so my deepdraw efforts did not come out as desired and I only used the top and bottom parts and had a middle section from extra sheet finally. So these are most likely the only pair in stainless worldwide in BMWs.
When dealing with ethanol fuel you can have some corrosion from collected water like holed float chamber from water in the bottom - had this some time ago - and I have this 69 S since 1972 and never had that kind of corrosion with olde time gasoline !

Vic

 

[LoneStar]

Beautiful work!

I've seen pitting at the bottom of zinc alloy float bowls as well, sometimes all the way through, but I suspect these had been left outside collecting water for a decade or two. I've reclaimed some with JB Weld to fill the holes, and a layer of Red Kote to protect the JB Weld.