SOHC.co.uk Forums > CB750

Overtight Keyster Airscrews!

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K2-K6:
Unfortunately it was my turning of the #3 screw that has brought the need of further work to the carburettor.

We had fettled through the various cables linkage etc to get a consistent and accurate closing and response to twistgrip control as it was giving Andrew concern with odd responses prior to that, this brought a more confident position that it would have correct control over engine speed.

Then looking at it's running it feels too rich with the throttle fully closed and needed input from throttle to keep idling as it would either quit when set at reasonable rpm or needed setting too high idle with the master tickover adjust to prevent that happening, hence then looking at the airscrew set point to consider fine adjustment and stable idle.

This is where the problem began with the keyster air screws, installed for Andrew by someone very familiar with working on carburettor they must have gone in easily (showed no signs of burring around the slot) but were very significantly tight to move at all. #4 came out although tight and we could compare to the original and see it had a slightly different profile.
#3 was very resistant to turn and so I used a straight and good fitting bit in a  1/4 inch drive socket with extension bar to get a very straight drive while holding the bit in full engagement.  This started to turn anticlockwise but then sheared one half of the drive slot from the screw as it wouldn't support the torque required to turn.
It just seems they should never be that tight and looks like they weren't when they went in , hence both of us being puzzled as to how that may have changed and was that specific to keyster materials? 

Conciuos that it's now caused more work in a one step forward then one backwards, but it's a really very nice original bike with low original miles, sounds very good mechanically along with the HM300 pipes having a particularly distinctive output too.  Very puzzling why the screws have ended up so tight when nothing appears to have been done wrong.

Andrew-S:
It's just one of those things Nigel, it could just as have easily been me the screw broke for, and probably would have. I dropped the carbs off with Mark yesterday (they still are a black art to me!) and he was surprised at what had happened, particularly as the screws went in easily enough and internally were in great condition reinforcing its low mileage.

With everything else that's happened in the last 2 years, I'm losing a bit of love for the K1. So these photo are for me....

Laverda Dave:
Stick with it Andrew, it will all come right in the end, a few days away from it will make the difference. In the words of Churchill when times were tough 'We shall never surrender' (maybe you can tell I'm a volunteer tour guide at the Battle of Britain Bunker in Uxbridge :)).

Andrew-S:
Thanks Dave, I'm sure it will come right in the end somehow and the old girl will be on the road again.

You cant beat a Churchill quote in times of need or down a bunker in Uxbridge!  :)

Andrew-S:
Phew! Mark managed to get the air screws out yesterday with a combination of heat, effort and an Easyout. :) He'll be giving the carbs another going over next week, after which I'll put them back on and fire the old girl up to see where I'm where I'm at.



 

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