SOHC.co.uk Forums > CB750

Slow Jet Size?

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Andrew-S:
I posted in a previous thread that a slow jet snapped off in the K1's carb body, see: http://www.sohc.co.uk/index.php/topic,25765.0.html

The broken jet was a 35, I thought the standard size was 40 which may have been contributing to why it wouldn't idle?

Thoughts appreciated.

Thanks,
Andrew

K2-K6:
It's possible it was used in a high altitude state originally,  for which that would likely be a decent choice in cleaning up an overall rich condition with quite an accurate shift.

For us lowland dwellers it's a reasonable sized step, but not completely out of range in that it would likely need to have the airscrew in further that manual specification to make sure it draws enough fuel with slides closed and minimal throttle. 

A screw set point of 3/4 out as a starting baseline would probably give reasonable start point to assess it overall as this would force you to lift the throttle slides very slightly for tickover speed, which would improve the progression at that point and make it slightly less sensitive to their exact position.

The benefits of running it on that setup (for this altitude) edging leaner that pure factory setting, is to push less unburnt fuel into the pipes that causes corrosion. That's if it feels like it runs ok when you get it out on the road.

Trigger:
The Manuel is wong on the 750K1 carbs. Ask Paul G as, i gave him the correct size when he was building his carbs and i can't find my little black book at the moment  ;)

Andrew-S:
K2-K6, the bike was imported from Wisconsin in 2009 from a long I believe a term owner so not particularly high altitude so it will be interesting to see what the other three slow jets are? 

Thanks Trig, I'll PM Paul.

Cheers,
Andrew

paul G:
Andrew,
                    If I remember correctly the manual states 120 mains but it will run rich with those in with stock setup.
I went down 10 to 110 on Triggers advice and it is miles better.
I didn't change the slow jet from stock.
Hope that helps

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