Jetting question

Wrong, the fuel tower will continue to feed fuel to the low speed jet, where it will mix with air, then this mixture will flow to the pick off holes behind the throttle plate and the pilot screw ahead of the throttle plate, whether the throttle is slightly open by the idle speed screw, or wide open. The low speed jet will always be supplying fuel, it doesn’t magically stop
this makes sense, The reasoning is the air feed into the low speed side of the carb continues to get air so long as the motor is running, even with the carb at wot, the low speed tube will still get air... so it should continue to get fuel through this system. i know of a lot of people who run the low speed without the lower o ring. top performers.
 
Ok some other thoughts . The tilly or walboro carb have the idle hole on the bottom ; the clone /predator have them up on the side . This should not affect the pressure differential factor , correct ?
Not correct.
There is a hole on the bottom of the Tilly, I don't remember that hole being on the bottom of the WD3. The Tilly uses that hole to sense the alternating vacuum and pressure in the crankcase. This actuates the pumper diaphragm. The WD3 uses a piece of plastic tubing to connect the carburetor to the crankcase. Same purpose, to actuate the fuel pump diaphragm.
 
I know my memory is not too good at times . I do trust and appreciate your knowledge .
Here's the but !
Which part is the side the needle side or the pump side ?
There is also the difference of a diaphragm carb and a float carb ( well maybe) pressure differential still has to move fuel out of the float bowl or fuel well .
It actually appears it's on the top left . With the fuel well above it .
What is your opinion on the air bleed effects ?
Your point is then , that fuel aways flows out of the low side .....
 

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Ok some other thoughts . The tilly or walboro carb have the idle hole on the bottom ; the clone /predator have them up on the side . This should not affect the pressure differential factor , correct ?
Though it should affect the amount of the pressure differential due to it being higher above the fuel level .
The last thing is the air bleed . There must be something there because there are rules govonering it .
 

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Wrong, the fuel tower will continue to feed fuel to the low speed jet, where it will mix with air, then this mixture will flow to the pick off holes behind the throttle plate and the pilot screw ahead of the throttle plate, whether the throttle is slightly open by the idle speed screw, or wide open. The low speed jet will always be supplying fuel, it doesn’t magically stop
don't say wrong when you just don't know.... it's not magic.... it's by design.... i'd explain it to you but then you have to say you were wrong.... and i'll let you keep thinking you are right...
 
this makes sense, The reasoning is the air feed into the low speed side of the carb continues to get air so long as the motor is running, even with the carb at wot, the low speed tube will still get air... so it should continue to get fuel through this system. i know of a lot of people who run the low speed without the lower o ring. top performers.
it only makes sense if you don't understand how the circuitry works... it's still wrong
 
1605296661991.jpeg

I was able to find this graph after Alvin had reworded something and I used it for googling lol this is a different type of carb but from mikuni manufacturing itself. This is a slide type carb. Would the graph be similar to a butterfly type carb?
 
My theory, a carburetor that's tuned, correctly, for racing will not idle well, a carburetor that's tuned to idle, correctly, will not race well.

These carburetors were not built for racing, they were built for engines that run at a near steady state RPM. They do that very well. We asked them to do something different, they need to be tuned different to meet those purposes.
a properly built SA /clone/predator carb will idle and not foul your plug... and will have power on acceleration will run at WOT if your carburetor won't it was hacked to make it run well at WOT (i would hope) and then you just suffer through the rest... anyone/hack should be able to make one run well at WOT...
 
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I was able to find this graph after Alvin had reworded something and I used it for googling lol this is a different type of carb but from mikuni manufacturing itself. This is a slide type carb. Would the graph be similar to a butterfly type carb?
a slide carb is no way like a clone/predator fixed jet carb
 
The low high side graphs should show similar . The slide restricts the throttle bore as does the butterfly .
Thank you. I know it’s not gonna be exact but it’s a reference. I know the two carbs are too different animals and are tuned completely different for sure. Just needed an idea of where to start. Time to start testing out jets now 😀
 
Air bleed restriction diameter have the same effect larger = leaner smaller = richer mixture.
But, just because you reduce the air available to the high speed circuit, doesn’t mean you improve performance, especially as timing retards
This entire conversation has some good points .
This is as much a statement as a question .
Closing the air bleed will richen the mixture , you want it leaner at high rpm which the air bleed is designed to provide .
For a simple 2 jet carb it's still a complicated device .
 
Good info , needed popcorn tho . What are your track or clubs rules for max jet size ? I would say you got it to rich on the low side , depending on how your build is , stock , SA or such . On a stock engine , I have been told a 18 or 19 is good low , and 31 or 32 is good for the high .
 
Good info , needed popcorn tho . What are your track or clubs rules for max jet size ? I would say you got it to rich on the low side , depending on how your build is , stock , SA or such . On a stock engine , I have been told a 18 or 19 is good low , and 31 or 32 is good for the high .
Guys who know zero about these sa carbs like alvin and others would rather disseminate bad/wrong info than just not say anything when they don't know... someone said "fuel tower" what? which part is that? because on carbs i build i have yet to see one or know what it is... why is a 18 or 19 a good low side? and why is a 31 or 32 a good main jet? if you do not address the emulsion tube and understand what it is doing and when.... the last thing you need to be worrying about is jet size....
 
Air bleed restriction diameter have the same effect larger = leaner smaller = richer mixture.

This entire conversation has some good points .
This is as much a statement as a question .
Closing the air bleed will richen the mixture , you want it leaner at high rpm which the air bleed is designed to provide .
For a simple 2 jet carb it's still a complicated device .
you are somewhat correct at wot the low side is all air... from the little brass orifice at the head of the low side to the pick holes to low air bleed screw... all air.... so this has a very small leaning effect....
 
Just now I am thinking if you remove the bottom o-ring .
Your effectively bypassing the jet in the low side .
 
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