Project Vento has begun: help wanted.

[Jordan]

I think it is only the fuel level that needs to be controlled.

Same difference, surely, Jordan?

But the capacity of the float bowl does not affect the operation or tuning.
Sometimes larger float bowls and float valve/seat were fitted for racing, when more fuel supply is sometimes needed.

[graeme]

What size needle and atomiser do you have ?

I just finished a ‘78 Darmah and had similar symptoms to you with the front cylinder.
I was sure I had a K6 needle and 262 atomiser.
Black unburnt fuel smoke at idle, bad hesitation and miss at part throttle but ok in the higher throttle openings.
I finally looked through a magnifying glass at the needle and it was a badly stamped K8.
Bought a new K6, problem solved.

Graeme

[ducwiz]

But the capacity of the float bowl does not affect the operation or tuning.

IMHO it does. It defines the control speed of the fuel level, for the engine's given fuel consumption. A small capacity i.e. a small amount of fuel reservoir results in an unsteady or "nervous" fuel level, which might have a negative effect for the bike's running characteristics.

Hans

[Jordan]

But the capacity of the float bowl does not affect the operation or tuning.

IMHO it does. It defines the control speed of the fuel level, for the engine's given fuel consumption. A small capacity i.e. a small amount of fuel reservoir results in an unsteady or "nervous" fuel level, which might have a negative effect for the bike's running characteristics.

Hans

That could be true in theory, but I am guessing that normal engine and road-induced vibrations would have a greater effect on fuel level stability?
Then again, perhaps there is a damping effect by virtue of a larger float bowl, yet to be demonstrated?

[DBDBrian]

As Ian states, a capacity would only be relevant to a given size of chamber. But as Jordan say, the fuel level is paramount, regardless of the type or size of float chamber, with which I would fully agree,
A large large chamber containing a high volume of fuel, is beneficial for a sudden high demand of fuel, this is also where the size of the float needle / valve comes into the equation, to maintain the fuel at the correct level.
Dellorto recommend the large SS1 chamber for carbs above 32mm. But having said that, Amal list the small, type 510 (matchbox) chamber for use with the later 1-1/2" GP. 2 Carb.
I have the large, type 504 chamber on my Goldstar, these were also designed to accommodate a very high flow if using alcohol fuel.

So my take on it for what it's worth, Jordan is correct that the size of the chamber is irrelevant when setting the fuel level and making adjustments. Hans also has a good point that a large reservoir would be less subject to a variation in fuel height.
Another point, the float chambers I have listed, are all remotely mounted , usually with some form of damping, also with a facility for height adjustment, which can be done visually with a clear tube. A big plus against a fixed chamber.

[Ventodue]

<snip>
Sometimes larger float bowls and float valve/seat were fitted for racing, when more fuel supply is sometimes needed.

But now you're changing the parameters ... Larger float bowl = greater capacity, for sure.

[Jordan]

Sorry, I didn't mean to evade the issue, just second-guessing the possible reason for focussing on float bowl capacity.

[Ventodue]

Sorry, I didn't mean to evade the issue, just second-guessing the possible reason for focussing on float bowl capacity.

Just another way of killing a cat, I guess ...

[cooperplace]

There's a vent next to the choke (sorry, starting enricher) that when I block it off, the choke seals just fine, as measured by whether i can blow thru it.

I put a hose on the fuel inlet and blew on it while fiddling with the float level, and it's clear that the human lung, even my decrepit examples, can supply more head of pressure than the fuel in the tank. BUT I think my float level setting is about 1mm out. I'll adjust this and start it and see how it runs.


Thanks everyone for the excellent advice.

[cooperplace]

I'm looking for custom tank decals (cheaper than paying for hand-drawn) for the words Ducati and Vento. I think it's called Guigiaro font.
has anyone found a place that can make these?
thanks