SOHC.co.uk Forums > CB350/400

CB400f - carb Air Screw query. Two screws different appearance ?

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400 Cafe Racer:

--- Quote from: K2-K6 on September 27, 2021, 10:15:12 PM ---That type (black plastic with limit stop) is used on small garden machine carburettor and possibly some other application too.

It's ordinarily a cap with limit stop incorporated that is pushed on to a brass airscrew with serated top. They'd be installed and adjusted to specification in "turns out" then the cap put on top to just allow limited adjustments in the field.

Wondering whether it's come from something like that.

--- End quote ---

Hi K2 - K6 and Ted,

You both posted while I was replying to Julie,

I think there may be other comments to come in later, but i guess my question would be.  Would you remove these "Caps" and is the normal screw what you find underneath ?. ;)

Thanks

Dennis

Laverda Dave:
The black plastic caps were fitted over the screws to limit the amount of adjustment by the owner as K2-K6 suggested. If you find all these still in place on a 400/4 consider yourself very lucky as they were frequently removed during a carb adjustment and lost (trying to put them back onto the brass screws on carbs 2&3 requires fingers six inches long and as thin as a matchstick)!
They are like gold dust to find s/h, you might find the odd one but never four together!
On a personal note, when I rebuild the carbs on a 400/4 (seems to be a frequent thing I have to do!) I adjust the air screw to two turns out and then replace the plastic caps with the stops at the six o'clock position. This will allow the air screw to be adjusted 1/2 turn either way.

McCabe-Thiele (Ted):
From my memory you do not remove the cap it's fitted to allow you the range within one turn of the screw - so if it says 1-2 turns the cap will be fitted in turn 1 position allowing  a maximum rotation of two turns before it hits the stop.

I left mine in place - I suspect you could remove them but not sure without going into my garage loft where the carbs are stored to check.

Laverda Dave:
The Haynes manual states two turns out Ted. That's why I set the plastic cap stop at 6pm position to allow an adjustment to either 1.5 or 2.5 turns out.

Laverda Dave:
They are easily removed, just lever them off using a thin blade screwdriver under the bottom edge just make sure you don't lever from one place as the plastic is soft. They are an interference fit on the brass screw, the screw has a 'spline' type finish as you will see from the second photo on the original post.

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