Float Needle Valve.

At least here in Finland the biggest problem is when the fuel dries it left some solid peaces or a thin solid layer on the parts inside carbs or fuel lines. That's why the fuel systems must be always dried, fuel stabilizer added or engine runned lastly with alkylate petrol for winter storage. Still I use fuel system cleaner at least every time a vehicle is taken out from the storage.
This dried fuel is very likely to jam the float for example and block jets and channels, worsest case can be a hole on the piston for example.

I think the reasons for these problems are reforming used when the petroleum is manufactured (fuel can not be storaged for longer periods), ethanol (corrosive effect) and national finnish oil corporation sell most of the higher quality propellant batches abroad and leaves the worsest batches to be sold to consumers in Finland. Biggest technical research center in Finland has stated that the propellants the corporation sell on local markets are mostly suitable for heating up buildings. On this use those burn very well and clean but are not suitable for motors.
Some engines need spark advance to be retarded with these inferior quality fuels, also the real octane ratings are quite low and difference between RON and MON is high (indicates low suitability to engines).

I don't know what kind of fuels are there when you guys live? Have you noticed any similar symptoms? I think at least the reformation process is widely used nowadays and some countries add ethanol.
 
CLEMTOG said:
thank you Cam,
we can both now rest our case.
CLEM
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Unless someone has an alternative theory  :D
Should the needle and seat be replaced by a larger item, than previously fitted, surely the flow rate would be greater. But, as pointed out by C&C would never be a variable flow valve.
 
chrisk said:
Unless someone has an alternative theory  :D
Should the needle and seat be replaced by a larger item, than previously fitted, surely the flow rate would be greater. But, as pointed out by C&C would never be a variable flow valve.
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I've fitted a #300 valve for testing, didn't notice any difference.  Reckon the #250 are big enough for just about all the clunkers are capable of. :D  If the fueling is OK with the #250, no advantage with going bigger.

piet
 
AndyW said:
Are you 100% sure about that?....
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I would not be. The float system is a negative feedback system that has parameters such gain and responce. The responce is set by float height, float weight, valve size etc. All of these are even adjustable in Dell'Orto. ;)
 
Just consider Gravity feed fuel pressure is constant all the time in check by Fuel Petcocks and the Fuel Bowl Check Valve that tends to leak under pressure as it is archaic in Carburated Motorcycles.

Electric fuel Pumps tend to be used with Fuel Injection that Shut Down when the key is turned off - No Fuel Pressure.

Gravity feed Carbs are always subject to fuel pressure unless the Fuel Bowl Float Valve seals (Perfect - Oh-Hum) - That's why one always closes the Tank Fuel Petcock after shutting off the ignition.

Don't matter if the Bowl Check Valve is perfect when the engine is running as long it is not so damaged the bike will not idle or maintain fuel bowl level when cursing or racing.

NEVER DEPEND ON A FUEL BOWL CHECK VALVE TO STOP THE FUEL FLOW  UNLESS YOU TURN OFF THE GAS - Ensuring the Bowl Fuel valve is outta the equation.

Really old school which Younger Members can't fathom when they are depended on the KEY -  Who needs a key over vibration when you can use a tough ignition toggle switch or simply keep the carb bowl float valve set in specs, clean and shut off the tank Petcock when the motorcycle is not running.

If you follow these old school rules you can easily determine if you have a corroded float check valve (perhaps a hard rubber tip or damaged seat which is very unlikely) or a saturated sinking float.

Carbs and Points are relatively easy to fix on the side of the road - Electronic Fuel Injection with ECM  pods are another matter yet Mechanical Fuel Injection is a dream.
 
sfcpiet said:
I've fitted a #300 valve for testing, didn't notice any difference.  Reckon the #250 are big enough for just about all the clunkers are capable of. :D  If the fueling is OK with the #250, no advantage with going bigger.

piet
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Oh well, that's:
The Melbourne Cup bet
$30 million Lotto draw last night
Wild sex with my wife last night
My needle and seat theory this morning

I've lost all the pre-mentioned in twenty four hours.
Seems I'm on a roll  ::)
 
The carb float valve is a shut-off valve with limited metering capabilities.  At rest, it simply stops the flow of fuel to the bowl.  With the engine running, fuel will be consumed from the bowl.  When the float drops under the pre-determined height, the valve will open and fuel will dribble through, (sort of) maintaining the pre-determined float height.  The higher the engine load, the faster/stronger the dribble.  Flow is controlled (when fully open) by the difference in valve cross-sectional area to valve seating cylinder cross-sectional area.  Dellorto valves with lower numbers are hexagonal in cross-section, larger numbers are square or triangular.  Metering precision is largely dependant on keeping the carbs isolated from vibration, this is also what causes the wear at the valve tip and the plunger stop.  As Dellorto valves are usually supplied with new seats, they should always be replaced together with these.

piet
 
At rest, it simply stops the flow of fuel to the bowl.
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And NOT spilling over into the throat of the carb and into the intake and onto the top of your pistons and into the crank case.

Carb Float Bowl Valves are never to be trusted and definitely not guaranteed, no matter there condition, to prevent the engine from excess fuel contamination unless you close the tank petcocks and thay have to be working.

Standard practice with gravity fuel feed carb motorcycles.

The carb float valve is a shut-off valve with limited metering capabilities.
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That I agree with you PIET. The word was "LIMITED"  ;o)

The Carb Fuel Bowl Valve act as a mean fuel regulator level when the engine is running - NOT a Fuel Shut Off Valve.
 
Very good one Piet.

I think the fuel level alters quite little on the bowl while riding, therefore the movement of the valve is also very small when it is somewhat metering the flow. But the fuel level must alter a little bit, otherwise the float can not open the valve. If vibrations are omitted, the fuel level must lower according to how much the engine sucks fuel. This if the movement of the valve is smooth, I don't know if the valve starts to oscillate at some conditions.

Have never found any Dell'Orto instructions how to select a suitable float (if something else than standard is needed), there is floats with different weights. I'm not sure if there is selecting instructions for the valve size.
 
Don't matter how much fuel is in the bowl when the engine is running as long there's enough to supply the engine demand. - You just don't want it to act a definitive stop fuel from the tank into you engine when you shut down.

So yes the Fuel Bowl Float does not have to be perfect as long as you got the float height set so that it does not over flow bowl or have it run dry.
 
SF: If everything is correct and kept clean inside the carbs, it really closes the valve. It has a viton tip. It will not flood then, but of course the carbs are evaporating fuel and the valves deliver more fuel according to that. I haven't got a single flooded Dell'Orto for last 15 years (as far as I have owned them), I overhauled them and kept them in good condition. Neither do my close relatives who have had them for decades.

Incorrect float level will affect mixture ratio.

I know a Laverda owner who used to left the taps open whole weekend on motorcycle rallies.
He wanted to annoy other motorcyclists, which had bikes with traditional fuel taps and valves without rubber tippings. People came to him and said that his taps are open and he answered something silly about their bikes. Same thing also with those Bosch spark plug caps which had sheet metal covers, people said him it will not start at the morning if it rains at night. And then he had a lamp connected to the big sized battery (similar to original) and kept it on for hours and the people said him they will push start his bike at the morning. And it did not flooded and he made a number how easily he started his Laverda at the morning. He used only his fingertip to hit a little bit the starter button while everyone else were watching. And the bike always started immediately. Then he was helping others to push start their bikes.
 
MotoJouni: I got fond memories of a Bar Maid push starting my SF down main street early in the morning to get me to work on time  - Due to a dead battery ;o)
 
sfcpiet said:
The carb float valve is a shut-off valve with limited metering capabilities
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Actually, I think you?ll find it has unlimited metering capabilities. Invented by Archimedes ~300BC, it is a flow control device incorporating its own natural PID controller (the performance of which instrumentation companies strive to match even to this day).

?simple shut off valve? ptuh!! ::)


 
Maybe it was only me, but I doubt it, I've had many troubles with valve needle/seat new sets. Maybe some bad quality replicas (one of them was built in Poland) but I would always recommend to check if all is going well after a replacement.
 
"I've fitted a #300 valve for testing, didn't notice any difference.  Reckon the #250 are big enough for just about all the clunkers are capable of. :D  If the fueling is OK with the #250, no advantage with going bigger."

I fitted 300's as well, because, a good few years ago, when I was younger and rode harder, I found that when "approaching" the point where you need to reach for the reserve function on the tank shut off valves (specially for Ron) that a misfire would set in and lead you to switch to reserve unnecessarily, having "calmed down a bit" later on, I would realise that I had not done enough miles to reach reserve and switch back to main, if I remained "calm" and did not give it the berries, she would run on for a good few miles, cant remember how many, too long ago, so I installed 300's and all was good, but later on when racing (same bike same carbs) in '86/'87 the problem re-occurred, trying to race on the minimum of fuel for the event, first half of race would be ok, but second half gave the same problems, but this time reserve was never "off", so I fitted a third pet cock and all was good again, but lets not restart that argument!
CLEM
 
AndyW said:
Actually, I think you?ll find it has unlimited metering capabilities. Invented by Archimedes ~300BC, it is a flow control device incorporating its own natural PID controller (the performance of which instrumentation companies strive to match even to this day).

?simple shut off valve? ptuh!! ::)
Click to expand...

Maybe, in an ideal world, or at standstill.

Considering its work environment when on the move, I'd describe the metering qualities of a float valve as quite limited.  Vibration and constantly changing fuel levels acting on the floats through lean angles or acceleraton and braking all help fuck up any precision the actual device might be able to achieve.  At best, one could describe it as "hit or miss"... but still good enough for the application.

piet
 
For Clems benefit, taken from a Dellorto handbook:

3.2.1 Selection of the needle valve size

For a motorcycle with gravity feed from a fuel tank, the fuel inlet valve size, stamped on the seat of the needle-valve itself, should always be 30 % greater than the main jet size.

In case of malfunctioning, you may find that the needle valve size is too small when running the engine at full throttle for a long stretch and that the engine rpm falls, due to the progressive weakening of the carburation.

Conversely, you may get repeated flooding in use where the needle valve seat size is too large.


Haven't seen a proper-running triple with mains larger than 160-ish, makes the #250 valve plenty big enough.

Please note that even carb makers call the device a "needle valve"! :D

piet
 
sfcpiet said:
Please note that even carb makers call the device a "needle valve"! :D
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Perhaps it's whoever translated the Dellorto manual into English  ;)

We're lacking a distinct word in the English language for the inner part of a float valve, so "needle" has become the default, which is probably where the confusion with needle valve arose.

A true needle valve needle has a tapered needle that goes inside a hole to vary the orifice area as it's inserted/withdrawn. The slide needle and associated jet in the carburettor is a good example.

A float valve just has a conical tip to centre it in the hole that it's closing off.

Here's an idea to try if you have a sticking float valve.
 
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