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Vacuum pipes on CB750FO

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Dave B:
I have got to the stage of trying to start my bike which came as a box of bits. IT won't start.
Carb jets were all very blocked.Slides seized.
I have cleaned the carbs and all jets are clear and slides and needles running free.
All four float bowls are filling with fuel but fuel does not appear to be passing through jets around the needles.
I have a good spark and good compression.
I have attached a picture of two tubes that i believe just vent atmosphere.
However when i apply compressed air to open tube end it will not pass through to inside of carb.
The tubes are new.
I have twice stripped the carbs and checked jets and floats.
Any ideas greatly appreciated,
Dave.

McCabe-Thiele (Ted):
I am relatively new to this forum but my thoughts are - When you blow down the main jet emulsion tube or up from the carburetta base is it a free flow of air ? I would use some rubber or plastic tubing to ensure a flow. If that is good then I would be looking at things like is there a decent level of suction on the intake side. Have you got the choke on plus air filter etc.

K2-K6:
To give a separation of cause,  lift the throttles and spray something like carb cleaner,  e-z-start into the throat, then try to start it.

If it goes then you know you're just looking at fuel rather than another problem mixed into the non-start.

The tubes are usually to vent the float bowls and stop them air locking into vacuum which would make the jetting variable in use. They should have clear passage into the carbs to work effectively. 

For any carb,  if the float bowls aren't ventilated properly, then the vacuum in the venturi can't overcome that created in the float bowl, so no flow will occur.

Dave B:
Yes main jet tubes are clear Air Filter and box in place Choke on

Dave B:
I will get some easy start ordered
Thank you

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