Walbro Flow bench

[ddracing]

We are looking at buying/building a flow bench mainly for the carbs on our KT100 kart engines. We would like to test the air boxes & their adaptors, carbs, etc. They are Walbro WB-3A carb with a bore of around .950". Since this is about the only thing we will be using this for, we didn't want to spend a lot of money buying one. Is is feasable to build one that gives us consisitent readings for a decent price? I have a nice shop & have no problem fabricating about anything so we could make it very precise but wondered if it would be worth the effort. Thanks for any help.

[larrycavan]

[ddracing]

Yes they are. They aren't very good for the application when you consider that the little flaps (pump) have to pump at 14,000 rpms plus. They are designed to run wide open like on a weed eater so they don't run very good (too rich) at lower rpms. But that's what we have to run in the can classes. I'm a little new to the actuall workings of a flow meter. Would the box have to be any certain minimum size? I might need a little more info for the actual location of the componets & what I would need for the construction of the manometers etc. So to get more accurite results, I might need to get more vacuum than a shop vac could produce? This would still be a lot better than buying an manufactured unit. Since we are dealing with a spec class, we are working on everything we can get down to the spec air box, carb adaptor & bolts, butterfly, etc. Any help is greatly appreciated. Thanks.

[larrycavan]

[106-1194218389]

Larry,
What I have been flowing with uses a shop-vac and with a small block chevy Iron Eagle 180 cc 2.05" intake it will pull 6" at .700" lift. I am using one Craftsman 6hp with a 16 gallon tank. btw the simple flow box you described is exactly what I am building right now. 24" square by 34" tall with the orifice plate in the middle so I have two chambers each half that height. I am using PVC Van Stone flanges to hook 2 shop vacs to it. I'll keep everybody appraised on how it works.

John

[ddracing]

How exactly do you calibrate the bench at first? If I use one of Bruces 100 cfm orifice plates, do I adjust the gate valve to pull 10" on the first manometer with nothing on the carb adaptor or does that not matter as long as you use the same test pressure everytime? Then to test, install the carb on the adaptor & read the upper manometer & the test figure is the difference between the two manometer readings? Then plug that number in you spreadsheet calculations along with the orifice size? Sorry for all the questions, but I want to do it right the first time. Thanks.

[106-1194218389]

To answer a question on how much depression will a shop vac pull: My Craftsman 6 hp rated velocity is 200 mph on the blow side will pull an honest 25" h2o when flowing a 1" orifice. So if you were to build a box like Larry described (which is what I am building) and have two ports for two seperate shop vac's you should have plenty of depression for what you want to do