Mikuni side mount pilot air screws

I seem to remember seeing this before, but I couldn't find it via the search.

Can someone remind me how the side mounted pilot air screws work? Is turning in rich or lean?

This are the Mikuni carbs with the pilot air screw on the side of the carb near the engine.

Thanks!

My understanding of air screws is that turning them out (counter-clockwise) allows more air to enter (leaner) turning them in reduces the air (richer). Ed

The pilot air screws on the side of the carbs control air flow to the pilot circuit and work as follows:
turn out to lean - by increasing amount of air
turn in to rich-en - by decreasing amount of air

The pilot or fuel screws on the bottom of the carbs control fuel added to the mix and work as follows:
turn in to lean - by decreasing amount of fuel
turn out to rich-en - by increasing amount of fuel

Thanks guys, that's what I thought. Always nice to get confirmation.

Topper wrote: I seem to remember seeing this before, but I couldn't find it via the search.

Can someone remind me how the side mounted pilot air screws work? Is turning in rich or lean?

This are the Mikuni carbs with the pilot air screw on the side of the carb near the engine.

Thanks!

Topper,
I believe on those Mikuni's you will have a Mixture screw that controls volume of Fuel/ Air mixed already. It should be Less mixture turned in, ie Lean. This is how most CV style carbs are. Screw in front of Vacuum piston, circuit controls volume of mixture made by pilot jet and Air jet.

Good Fortune!

Motor Head wrote: I believe on those Mikuni's you will have a Mixture screw that controls volume of Fuel/ Air mixed already. It should be Less mixture turned in, ie Lean. This is how most CV style carbs are.

Thanks Moto Head.I don't think these are like most CV carbs. The screw is on the side of the carb and close to the engine.

I think 650Ed and gd4now are right here.

The Air Screws are usually behind the Slide, near the Air Jet, at the back of the carb. I don't have a circuit diagram for your carbs, but would think being between motor and slide, that they are mixture volume screws.

Topper wrote: ...Can someone remind me how the side mounted pilot air screws work? Is turning in rich or lean? This are the Mikuni carbs with the pilot air screw on the side of the carb near the engine. Thanks!

Referring to oem carbs on one of the two models shown in sig?
1979 KZ750 Twin? 1988 KZ305 LTD? Some other carb?

The following might possibly be helpful:

www.wgcarbs.com/index.php?option=com_con...view&id=27&Itemid=27



Good Fortune!

OK I had not paid attention to the models of bikes you have noted in your sig. My response was related more to the mechanical slide carbs (VM style) and not the diaphragm ones (CV or BS style) So which bike are the carbs in question from. The 750 or the 305. If it is the 750 then they should be BS38s for the 1979 750. I am not sure just what was used on the 305 but would think they were either BS34s or 32s.

IIRC there is a side pilot air screw on the BS38s, but on the BS34s and 32s the pilot adjustment screw is on the top of these carbs and does work differently than the ones on the side do.

This is for the '79 750 twin. I actually need to remove the 305 from my sig.

I was all excited when the first two responses confirmed my recollection, but now it sounds like there's still some doubt.

OK so it is the BS38s and for them I think that the mixture screw works as follows

Turn in to lean
Turn out to richen

You might want to check out this link www.amckayltd.com/carbguide.pdf though it is for the Yamaha 650s some of them use the BS38s and there is some good info in the document.