precision float level adjustment.

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texasSlick said:
If you apply a U tube shunt between the carbs, as gtiller shows in Reply #10, the fuel level in both carbs will come to the exact same level, regardless if one float is slightly higher/lower to the other.

Slick
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Whats the big idea of solving this problem so easily? Are you some kind of a trouble maker? (joking). Now I need to drill and tap the drainplugs on my little PWKs.
 
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texasSlick said:
If you apply a U tube shunt between the carbs, as gtiller shows in Reply #10, the fuel level in both carbs will come to the exact same level, regardless if one float is slightly higher/lower to the other.

Slick
Click to expand...

Just thinking out loud:

If you are going to permanently interlink the carbs via the float bowl drain plug, then why not go the whole hog and remove the float and needle valve then block off the banjo on one side.

I wonder if one needle valve can flow enough fuel for two carbs on a road bike?

Although I highly doubt it would satisfy fuel demand on a race bike.
 
See the date on the pix?
Been talking about it for over thirty years and eventually anyone would get tired of being a broken record!
Notice where the arrow for fuel level measurement is?
From bottom of BODY to top of fuel (Not meniscus)
All the action parts are attached to the BODY... not the bowl?
By 1990 I knew real well how the carbs worked.
Use this similar design for my 4 carb 95 kx900 kawasaki. sold it...


precision float level adjustment.


precision float level adjustment.
 
gtiller said:
Just thinking out loud:


I wonder if one needle valve can flow enough fuel for two carbs on a road bike?
Click to expand...

We Monobloc guys having one float bowl and a chopped carb know that one needle and seat, having the standard 0.125 inch orifice, starves a 750 engine at revs over 5K. My Atlas has a special needle and seat with a 0.200 inch orifice which does satisfy the engine, but I do not think there is very much reserve.

In my opinion, the only performance advantage of a concentric vs monobloc is the dual needles and seats .... you would not want to give that up.

Slick
 
texasSlick said:
We Monobloc guys having one float bowl and a chopped carb know that one needle and seat, having the standard 0.125 inch orifice, starves a 750 engine at revs over 5K. My Atlas has a special needle and seat with a 0.200 inch orifice which does satisfy the engine, but I do not think there is very much reserve.

In my opinion, the only performance advantage of a concentric vs monobloc is the dual needles and seats .... you would not want to give that up.

Slick
Click to expand...

There were available float bowl extenders for monoblocs did you try and if so did it work ?
Paul
 
HRD said:
There were available float bowl extenders for monoblocs did you try and if so did it work ?
Paul
Click to expand...
I've never known those float bowl extensions to make any difference
 
Danno said:
Someone should engineer a float pivot shaft with an eccentric that could be adjusted externally while the engine's running for dynamic testing.
Click to expand...

I like the way you think. This should include cabling and two HUGE levers mounted, one on each side of the handle bars, so one can make adjustments "on the fly". Might as well add flags on the ends of the HUGE handles.
 
HRD said:
There were available float bowl extenders for monoblocs did you try and if so did it work ?
Paul
Click to expand...

All the extenders do is hold off fuel starvation for a second or two. The needle and seat is the bottleneck.

For data on fuel flow thru various needle orifices, see ....

https://www.accessnorton.com/NortonCommando/flow-measurements-on-ewarts-fuel-tap.21225/

There was a thread on this forum several years ago, in which was discussed the fuel requirements for a 750 Norton engine WOT at full load. According to that discussion, nearly a pint of petrol per minute is the Norton's appetite. If you review the fuel flow data in the link above, one does not get that much with the standard 0.125 inch orifice needle seat.

A lot of guys running dual monoblocs, one chopped, find their bikes (Atlas's and the hybrids) "poop out" over 5K rpm and WOT. Most think that is all those bikes can do, but they are simply running out of gas.

Slick
 
Dances with Shrapnel said:
I like the way you think. This should include cabling and two HUGE levers mounted, one on each side of the handle bars, so one can make adjustments "on the fly". Might as well add flags on the ends of the HUGE handles.
Click to expand...
I just like overthinking simple things and making them more complex.;)
 
So the estimates here show fuel consumption at between a third and half a litre per minute at full throttle in a race bike......that would indicate 6 to 10 litres for a 20 minute session, which is normal track time per session here in France.

In practice with my 750 I normally use a base of 5 litres fresh fuel and then add 3 litres for each session, and I normally end up with 3 to 4 litres to drain from the tank at the end of each weekend.....

Considering that some of that fuel is used starting and warming up and in the collecting area, sighting laps and return:

Do I need open that throttle more :(
 
Danno said:
I just like overthinking simple things and making them more complex.;)
Click to expand...

Hey, Mercedes, BMW and Porsche have been making a ton of money over the years doing exactly that!

MB/BMW/P designers: "Why use 3 parts to accomplish a function if we can use 8?" :)
 
SteveA said:
So the estimates here show fuel consumption at between a third and half a litre per minute at full throttle in a race bike......that would indicate 6 to 10 litres for a 20 minute session, which is normal track time per session here in France.

In practice with my 750 I normally use a base of 5 litres fresh fuel and then add 3 litres for each session, and I normally end up with 3 to 4 litres to drain from the tank at the end of each weekend.....

Considering that some of that fuel is used starting and warming up and in the collecting area, sighting laps and return:

Do I need open that throttle more :(
Click to expand...

Do you not close the throttle at some points, during a lap?
 
Equal fuel levels make a lot of sense.
Seems the best way to achieve this is dual lines from the float chamber with the bike level.
I have one, need to source or build another.
 
gtiller said:
Just thinking out loud:

If you are going to permanently interlink the carbs via the float bowl drain plug, then why not go the whole hog and remove the float and needle valve then block off the banjo on one side.

I wonder if one needle valve can flow enough fuel for two carbs on a road bike?

Although I highly doubt it would satisfy fuel demand on a race bike.
Click to expand...

Single float needle flow capacity is one problem. The other challenge is the float level of one carb dictating the level in an adjacent carb. To solve this I think I will design a carb and name it concentric! All kidding aside, even if you had a single common float bowl located between the two carbs with ample flow capacity there will be problems.

To illustrate this without getting into vector diagrams of a less than perfectly coordinated turning motorcycle, think about a motorcycle engine in a side car. During a turn with two carbs and a shared (or coupled) float bowl, one carb will lean out while one will become richer. The concentric carb more or less solves this problem.

As for setting float levels, it’s the level that is critical, not the volume. The apparent “cease to idle” variances Jim is seeing are most likely due to differences in float volumes and weights.
 
My idle is good but I'm looking for perfection. I notice one side drops RPM a little on hard braking then clears up when sitting still which may be due to too high a float level on that side - shown by one side running longer before dying with the taps shut off. Made an adjustment but haven't tested it yet - its an ongoing thing.
 
jseng1 said:
.......... Made an adjustment but haven't tested it yet........
Click to expand...

It’s the fuel levels, not the fuel volumes in the float bowls. How do you know one of your cylinders is not consuming idle fuel a bit faster than the other?

Looking forward to hearing about the test results compared to dyno exhaust gas analysis and power differences, if any.
 
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