xs1 1969 nearing completion

[TC2000]

Thanks,
Rubber discs are ok on both. Using the left one = no leak and slide drops very slowly as it should.
The question of the groove remains : why this groove since it opens a small permanent passage between the diaphragm chamber and the starter circuit ???
On which machine was it used?

 

[TwoManyXS1Bs]

Yes the starter circuit affects the diaphragm on CV carbs. It could be that groove that's the problem, but you might look closely at the rubber disk on the end of the plunger, I believe that makes the seal to a ridge in the carb body, if the rubber is hard and or deformed and doesn't seal, the diaphragm drops faster.

Yes, that groove doesn't belong there. Don't use that plunger. The XS2 and TX650 used the same '306' plunger, which had only one interchangable revision, but NO grooves. This starter circuit diagram would generally apply to all the BS38 carbs, and shows that a groove in the plunger head would certainly cause air leakage.

The plunger heads of the '256' XS1-XS1B/F choke plungers were smaller in diameter.
A pic for reference:

 

[TC2000]

Thanks 2M,
I have fitted the plunger with no groove: works fine.
I will look a the older xs1 carbs later, with the small diameter plungers