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Old 24-09-2019, 03:15 PM   #5
Darkness
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Join Date: May 2007
Location: Stockbridge
Bike: M900
Posts: 1,984
Quote:
Originally Posted by Darkness View Post
I’ve had those symptoms before, and it was a holed diaphragm, but that was on a Stromberg carb on a Vauxhall HC Viva.
It was a fairly small hole.
With small throttle opening there was low vacuum, so the piston and needle didn’t lift, but wasn’t meant too anyway.

At full throttle there was enough vacuum to fully lift the piston and it felt fine.

The problem progressively became worse at anything between full throttle and idle as the air leak was sufficient to stop the piston and needle lifting as much as needed: the engine ran very lean with no usable power. I got home by red-lining it off the line in first, then changing up to top and trying not to press the accelerator as it would bog down and need another blast in first to keep it moving.
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