Wb3a

[Tom Rickard]

When i set up a carby i get the front of the body machined out in a "bell" shape and the air bleed jet is totally removed. I got given a carby set-up like this and it went well, and i copied it a couple of times and they both went the same. Never quite understood why. Never found a quicker carb though. Because of this i don't place great importance on the principle of air bleed into the low and transition jets.

[al nunley]

We could settle this further if everyone would take a picture of their best carb and post it here. Let's see how many line up and if that is what makes a fast one fast.

Grab that digital camera right now, go out in the garage, take that carb apart and take a picture. People want to know.
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If the data does not support the theory, get a new theory. (Al Nunley)
All else being equal; Compression is the Holy Grail.
45 years, in and around karting

[John Mulvihill]

Hi Walt,

Thanks for the compliment on the pics. Cameras just keep getting better and I just have to squint more. Nikon D70 DSLR set on 'close-up' with a short telephoto lens. Not a macro lens or screw on magnifying lens.

Re the sir correction jet, here is a link to a Walbro manual (courtesy of EC Birt):

http://www.eccarburetors.com/pdf/WB-Manual.pdf

In the drawing of the carb at full throttle, Walbro does show some air coming through the air pre-mix orifice and mixing with the gasoline in the trough. If correct it may be due to the way in which Walbro has positioned the entrance to the orifice in what looks like a higher pressure area just before the venturi.

By any chance do you still have that really bad carb or did you ever figure out why it didn't work well? Finding what doesn't work may be as important as finding out what does work..........

Tom,

A bell shaped entrance would be neat. It would at least give our tech folks a chuckle as they DQ'd us. That's a "Don't you dare touch!" area under our rules. We also aren't allowed to run velocity stacks and we have fairly tight rules on the air filter adapters dimensions.

Maybe that's why the differences between carbs get so important?

Al,

Good idea on the photos. I'm going to dig out all my carbs this weekend and go through them all and check for dimensions, etc.

Anything odd and I'll take a pic. Photos of the guts of poor carbs might also help.

John
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I bowl overhand..........

[George Clausen]

Colin, The two really "good" WB3's I have are both Cass City Mich. mfg.
Al, Totally agree on % numbers, would take a much larger sampling base
John, may well be something to the hole placement, but I wouldn't bet the farm that they would need to be centered. may actually need to be off center to create a swirl ?
And now another reason to have a wet flow bench! Anyone have any plans or DIY ideas for one. I don't like the idea of running dyed water through my dry one
George

[John Mulvihill]

Hi George,

Yup. I agree on the swirl. And, here is another variable I noticed.

Take a look at the fuel channel leading to the emulsion trough. In the silvery carb the channel leads straight into the top of the emulsion trough. In the darker colored carb (different alloy?), there is a "dogleg turn" where the channel hits the top of the trough.

That has to result in a different swirl pattern.

George, when you get a chance could you take a look in those two good carbs and let us know what you see?

I have another one I have to pick up from a friend and take a look in it on Sunday.

Thanks,
John
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I bowl overhand..........

[Todd Bellew]

A wet flow bench humm. There is some technology out there.

Here's a good article.
http://www.carcraft.com/techarticles/116_0612_cylinder_head_flow_bench/index.html

SO here's what I'm thinking for a DIY on these types of carbs, let me know.


A large vacuum motor sucking through a clear tube made to attach a carb. Since where doing visual observation sizes and such aren't as critical a say a flow bench. But, you do need to make appropriate judgement as to what the level of flow is to as closely as possible simulate actual flow volumes.

Simply turn out the lights and fire up a strobe light. I bet the fluid would "shine" /reflect light and be essentially visible.

You guys figure out how to make the pump pump and what fluid to use. Looks like the commercial guys use some dye and a black light. Not sure it needs to be sophisticated for this. But, I see the beneift now. Light constant on, and shading from the strobe could limit viewing.


This application is easy since where you want to actually see isn't buried through and intake manifold through an intake port and around a valve and into a cylinder on the top. etc lol
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Thank You,
Todd Bellew

[Todd Bellew]

Also, swirl is great but air doesn't just swirl on it's own. The shape of the "pipe" or path creates it. Like fuel moving around a valve on a certain intake port angle to have the mixture enter the cylinder towards the side and create swirl. Or obvious swirl shaped openings that create it. Some times obstacles in flow path can create swirl, like the shape of an intake valve itself.


What's creating laminar flow that rotates, swirls? I'm not denying it, just not understanding.
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Thank You,
Todd Bellew

[George Clausen]

Todd, I'm thinking along just those lines, simple manometer/s and clear viewing chamber
My current bench uses 2 or 4 Lamb 12 amp motors and interchangable involute shaped venturis.
I'm thinking one 12 amp motor and a sharp edge orifice sized for @60 CFM
George

[Walt Gifford]

I have a vacuum devise called a KT100 and a mixture sensor called an EGT that can be mapped with RPM throughout the usable range with a Mychron 3 basic. The test fluid is gas and oil that is burned after mixing to take the temp readings. Results produce two dynamic data curves (rpm vs egt) that are specific to the actual track you're tuning for.


Gif
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FAA certified jet engine and aircraft technician
Nicholson Speedway class champion 2001
Yamaha KT100 Service Center
40 years karting experience

[Todd Bellew]

I'll bite Walt since no one did.

I agree if your good enough to have a driver that can drive consistent, have the right tires on all the time you might be able to see from track data which carb is better. Or if you,re on a dyno you can probably see the differences.

So now I come to you and say show me your best carb and show me your worst. Can you tell me WHY one is better than the other? Or can you just say one is better without knowing exactly why?


I'm intersted in the why. I can take your best carb and worst carb and see why it's better with a wet bench.

Afterall, this entire thread is about the why. We already concluded years ago some are better than others and we have ways to find them.

But, WHY?

This way you build knowledge base, not just part a is better than part b.
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Thank You,
Todd Bellew

[George Clausen]

Yep... what he said
George

[George Clausen]

Actually Iv'e rethought the vacuum source requirement some. It would seem that an ideal source should duplicate the pulse/reversion that the carbureor "sees" on the manifold. Perhaps a motored "dummy" engine in the intake air stream to modulate and mimic the actual airflow. We all know that a steady depression is not the same as current test conditions. Might take some pretty sophisicated transducers to get this all working but I would think it might be worth pursueing.
George

[John Mulvihill]

Hi George,

Wet Flow (AFAIK) is mostly a visual process.

Might be able to do some of it with WD40 (dyed?) feeding the carb, a grounded ignition, and a starter motor spinning a KT100 over along with a camera looking down the carb?

Modify the aluminum spacer with an LED or something similar and strobe it?

Heck, I'm still thinking about the holes in the carb....... Took 11 carbs apart last night.

John
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I bowl overhand..........

[Todd Bellew]

All vacuum motors create a "pulse". Some like a shop vac have super high rpm "fans". Each pass of a fan blade produces a "pulse" it's just so fast and so often it feels as a constant "draw"

FOr example I recently tested a machine that had a "pump" vacuum not a fan per se. Like a compressor running in reverse. WHen open and running it pulses so much it almost feels as if it's blowing air out. It is, in between sucking air in. The pump turned much slower you could feel each draw from the motor. This type once sealed can draw a much lower vacuum than a fan type.

I'm not as sure this is as critical. I've seen where many builders claim that at thousands of rpms you can imagine the flow as a constant flow not stopping and starting. I guess once you attain enough pressre to start air compression inthe carb, while it may so briefly "stop" the entire flow is moving forward some just slowing down or speeding up but always moving in one direction. The compressive nature of a gas might allow this. SOrt of a spring that ocillating that you shot out of a gun. It's always going forward but some parts of the spring are travelling at slightly different velocities.


I do think matching the volume or essentially the correct pressure drop on the back side of the tube.

If you were going to hook one to an engine just make a manifold of plastic to move the carb back and allow viewing inside.

The spray pattern is going to be small and mostly contained in the carb. we've all seen what it looks like spraying contact cleaner and air through them. Pretty quickly the fuel completely atomizes and shows no pattern that can be discerned with the naked eye.

I say keep it simple to start with to make sure it makes any sense. Just draw a best guess amount of vacuum on a clear tube and see what happens.
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Thank You,
Todd Bellew

[Mark Horne]

Next time I put an engine on the stand I will try to focus a video camera down the carb and use a Strobe to stop the spray. I have a known JUNK carb and a couple good carbs of my own. It will be interesting to see if there is a pattern difference at least from the front. My guess is there will not be much to see.

I can tell you we have seen fuel/air mixture blow out the front of the carb at RPMs up to 11000. I do not remember seeing any at peak horsepower or above, BUT, that has not been on my list of things to watch during the pull.

I have not used a flow bench to test carbs, just used the dyno to see which carb makes more power.


It seems there is always something else to test.

Have a great day,
Mark
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