Reed testing on a stock 31158 reed cage

My next batch of tests were 6 different reed sets on a stock 31158 WB820 reed cage.

The top 4 sets are the ones that Ryan Courts sent to me for evaluation. I will test the G.E.M. G1158 reeds as soon as I figure out where I put them.


My calculations show that a WB820 needs 38.0 CFM at 8,000 RPM. The Boyesen 620 results surprised me. Might need to dust off one of the engine dynos. :^)

Mower parts

Part of this flow testing project is to find better flowing filters for my space restricted JLO powered Nethercutt MK1s.

I was hoping for a better number from the Tecumseh 35066 filter because it is small, fits HL carbs, is cheap and is still available brand new. 

It flows 39.0 CFM which is better than the 36.0 CFM 29661 Tecumseh foam filter and the 35.0 CFM cut down A11552 CASE filter that I have been using for over a decade. The adapter has an 11/16″ bore that I will punch out to 3/4″ and try again on the bench.

This filter is stock on some Tecumseh TVS lawn mower engines. The early TVS engines use the same recoil that we are currently using on our WB820s to replace the troublesome FM recoils. The later TVS engines use the 35000A cup that we also use on the WB820s.


Pretty much spent the weekend repairing fences so I was only able to sneak one test in. 

I expected the HL-375A racing carb to post a big number. I just did not expect it to go off my calibration scale.

It flowed 105 CFM which is more than double a stock HL-173A.

All my testing is per SAE J607, 3″ Hg pressure drop corrected to 29.92 Hg and 60° F.

820 flow bench testing

I flow tested 3 Tecumseh air filters, 1 Wacker cover, 1 West Bend housing and an Azusa velocity stack last night. I ran the tests on the HL-173A carb that Wilma sent me since it is bone stock and is what most Rokon 820 engines have. I did not use an elbow. I am looking for an air filter system that is currently available that does not hurt horsepower too much. I will run more tests on larger carbs since I suspect some of the Kart guys might also be interested in this.