Project Vento has begun: help wanted.

[Ventodue]

1. I can blow thru the choke pick-up whether the choke is in or out, if you see what I mean. <snip>

Not good, Peter. That choke MUST be 100% fluid tight when the choke lever is off.

1. Make sure you have some slack in the cable. It mustn't be lifting the piston off the jet, not even by the tiniest amount.
2. Visually inspect the top of the jet for any corrosion damage. This isn't usual, but can happen.
3. Fit a new piston. They're not expensive.
You can mess round with prising the old seal out and flipping it over; but IME it's not worth the effort, not least because the old rubber will be as hard as nuts and most probably won't seal even when flipped.

2. Idle jet is a 55.

That will be fine. (It's the standard spec for the 'Slow' cam).

3. I'm not sure if I correctly set the float height.

Ok. Forget what you've read elsewhere. Just follow the instructions from Dell'Orto ...

Take the carb off the bike.
Put it on a flat surface, this way up

Setting float height carb orientation.jpg

Fit a piece of tube over the petrol inlet spigot ...

Setting float height petrol inlet.jpg

Now, by blowing lightly down this tube while using your gauge, you can accurately assess the exact height at which the needle valve is closing.

Float gauge.jpg

Trying to do it in any other way can easily lead you to judge the valve to be closing later than it really is. Which makes you adjust the floats too high = too much fuel in the float bowl = rich mix at start up.

P.s Obviously, when adjusting the floats, make sure they're set nice and even. You don't want one lower than t'other.

And before you put the carb back on, perform this simple but essential exercise:

"1. Remove the idle jet and the mixture screw.
2. Using a can of carb cleaner with an extension tube fitted, put the tube up the hole where the idle jet goes. Cover the mixture screw hole with a finger. Squirt cleaner up the idle jet hole while looking for a stream coming up into the venturi, just in front of the back edge of the slide.
3. Now put the tube in the mixture screw hole. Cover the idle jet hole with a finger and squirt cleaner whilst looking for a stream coming out between the slide and the engine.
4. Now put the tube into the little air hole under the main carb air intake (not the "middle" one: the one on the side). Squirt, and look for cleaner in the venturi."

[cooperplace]

Vento,

that is fantastic, very useful. Much appreciated. I will follow this advice.

Thanks

Peter

[Jordan]

For PHF, Malossi used to sell a transparent float bowl with a line moulded in - presumably the correct fuel level.
Is this a good thing that can be trusted for all types of engine and float types?

[Ventodue]

Dunno, Jordan. No personal experience.

However I do have it on good authority that for the 32 and 36 PHF carb the capacity in the float bowl should be 58 ml.

[Jordan]

I do have it on good authority that for the 32 and 36 PHF carb the capacity in the float bowl should be 58 ml.

Is the capacity important?

[Ventodue]

Is the capacity important?

Well, yes. It's what you're controlling with the float height.

Btw, this thread has inspired me to ask 'People Who Know' just WHY the float height is so important - i.e. what exactly is it doing? And here's the answer I've received:

"The float height determines the fuel level in the atomizer tube. So:

If it’s too high, the depression in the venturi will cause excess fuel to be drawn up the atomizer resulting in a too-rich mix at low throttle settings, typically at start-up and idle.

If it’s too low, insufficient fuel may be drawn up the tube at middle and high throttle settings, potentially resulting in valve or even piston damage."

All comments welcome, of course ...

[Jordan]

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

[Eldert]

Peter

is the O ring still in place and in good shape ? part number 53 in the diagram .

Eldert

[Ventodue]

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

Same difference, surely, Jordan?

[ranton_rambler]

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

Same difference, surely, Jordan?

For a given size of float chamber, yes. But the height of fuel is what controls the relative pressure compared to the the intake vacuum and therefore the way the fuel is drawn through the different jets at different operating points.
Ian