Weber 40 idf no vacuum

[Dean.s]

I ran my engine up today with new fuel hoses and filters.

It started fine and ran really good. All ports were equally balanced.

Then i noticed 1 was misty and the throttle plate could not be seen. This mist cleared under high revs but reappeared at idle. There is no vacumm pressure there but the other three are still balanced.

The throttle plate in this port also looks wet whereas the other 3 look dry.

All ideas as to the issue would be appreciated.

[Nine One One]

Is the throttle plate actually moving? The screws holding them in place can come loose and hence it may just rotate on the spindle. The wetness indicates the jets are actually supplying fuel whilst the plate is closed or semi closed, and the others are dry because they are working correctly and turning.
Without starting the engine, just look down the venturi for the effected carb, and use the throttle linkage to see if that plate is actually moving on wide open throttle?

[Dean.s]

The throttle plates are secure and operates as it should. I've run it up cold and it still has no vacuum.

[Nine One One]

Inlet valve for that one cylinder?
What happens if you put the palm of your hand over that one venturi opening?
Check the push rod is secure in the socket, or the actual pushrod itself is not bent?

[Dean.s]

It is valve related. A nut had come off one side of a rocker arm!!

Thankfully it was happily sat on the edge of the head when i took the cover off!!

Lucky escape. One pushrod is fine. The other i can't get at without dropping the engine. I will have someone spin by ratchet the motor after i reassemble the rocker and I'll watch to see if any irregularities.

[Dean.s]

forgot to ask what thread size the nut is that holds the rocker shaft in place. none of the taps i have fit the nut.

TIA

[Bruce M]

M7 x 1.0

[neilbardsley]

Any chance the secondary Venturi is loose in the bad cylinder?

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[Dean.s]

Finally got around to refitting the rocker shaft. threads have held and the motor is running lovely again. thanks for the help.