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Posted by: Ansbacher Apr 25 2019, 01:10 PM

Every time I need to adjust the accelerator pumps on my Dellorto DRLA carbs, I can never remember which way to turn the nuts (clockwise or counter-clockwise) to increase the volume pumped and vice-versa. Can someone remind me? Thanks.

Ansbacher

Posted by: pilothyer Apr 25 2019, 04:24 PM

If you are referring to the pump shaft nuts, they were never meant to be used to adjust the volume of fuel pumped. You can, however adjust the volume with either a heavier accelerator pump spring (to increase the volume) or larger pump jets or possibly larger idle jets (one size up)
To simply answer your question clockwise will yield a longer pump stroke and counter clockwise will yield a shorter one.

Posted by: Ansbacher Apr 25 2019, 05:59 PM

Thanks, that's what I needed to know- clockwise to lengthen the pump stroke. Not sure I know what you mean by them not being intended for accelerator pump adjustments, but in my experience they have a great effect on remedying off idle bog.

Ansbacher

Posted by: porschetub Apr 26 2019, 02:06 PM

excellent answer,the Dellorto handbook should have quantity per/stroke which you set to.
I did my Zeniths after I rebuilt them,one was fine and the other was out a little, I found this was caused by wear on one link arm roller that runs on the throttle cam on the left carb.
With this repaired I didn't have to adjust the screws as it was close enough,I did notice some wear on both throttle cams so have a new set to fit some time.
Good luck.

Posted by: Ansbacher Apr 26 2019, 03:49 PM

After exhaustive reading on this subject from other sources, I am convinced that the pump jet nut controlling stroke length DOES control the VOLUME of the shot delivered, while the actual pump jet itself controls the RATE the shot is delivered.

Ansbacher

Posted by: yeahmag Apr 26 2019, 03:52 PM

Exactly opposite. The stroke controls duration (which as a side effect will control volume). The jet is the main adjustment.

When and where is your bog?
What is your timing at?
Engine specs?
What carb body, venturi, idle and main jets are in the carbs?

-Aaron

Posted by: rhodyguy Apr 27 2019, 08:52 AM

If the nut is too tight the jets will dribble fuel. Which del book do you guys use? The CB del book is terrible.

Posted by: Ansbacher Apr 27 2019, 03:52 PM

Thanks Rhodyguy for the heads up. I only have about 5mm of threads exposed so I think I'm OK.

I think the semantics of VOLUME and RATE got a bit unintentionally confused in this discussion. The pump jets and the stroke BOTH contribute to the overall volume of the delivered shot. Since it is not easy to change the jets themselves insitu, it only makes sense to adjust the stroke to at least govern the volume to some degree. That is why I adjust the stroke to adjust the VOLUME.

Ansbacher