Mixture Screw

[go_hercules]

From what I thought I understood all these years was that if the mixture screw was on the engine side (forward of the carb slide) then it was a fuel screw. And if it was on the airbox side then it was an air screw. Well, everything I have read says that the screw on my Dirt Squirt carb (Mikuni VM20) is an airscrew. However, the screw is on the engine side near the intake manifold. So what gives? Is there any way to verify what it is, like blowing through it to see where it comes out maybe? I would like to know for sure. thanks.

[Bullfrog]

I'll try to find a stock Squirt at Hodaka Days and poke around it to check your question out. I've always been pretty sure that all the factory installed carbs on Hodies had pilot air screws . . . but I can't state that categorically.
Ed

[go_hercules]

Thanks for that. I might take the carb apart to see if I can trace the circuits out and verify it for sure. Probably is an air screw but why it would be on the front is pretty unusual. Thanks.

[go_hercules]

Well I finally got back to looking at this. With the carb off, I took the mixture screw completely out. Then with a small hose I blew into the hole. Air came out of one of the small holes at the air filter side of the carb. So, it is indeed an air screw. Everything I have ever read said that if the screw was on the air filter side it was a two stroke carb and the screw was an air screw. And if the screw was on the intake manifold side it was a four stroke carb and the screw was a fuel screw. Well it ain't always so I guess. Now I know for sure.

[Bullfrog]

With the slide lifted up (full throttle position), how tall is the brass "spray bar" which sticks up from the bottom of the carb throat? That is one my "go to" ID features to identify whether or not a 4-stroke Mikuni carb might have migrated somehow to a two stroke.

Common "spray bar" height on a Mikuni two-stroke carb is about 8mm. Four stroke carbs commonly have only a 2mm height at that location.

Ed

[Hydraulic Jack]

The 26mm Mikunis used in the RD350 Yamaha reed valved two stroke road bikes have very close to zero atomizer height. There is nothing absolute about the height of the atomizer and the combustion theory of the engine.

[go_hercules]

I checked and the Dirt Squirt height there is about 3mm. But I know this is the correct carb so I just think these carbs were a little unusual.