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I have a 900SS with 32mm Dellortos and it was running fine and suddenly the rear cylinder goes rich. I expected a bad needle and seat or dirt causing the float to hang, but it's not to be. Insides are clean all jets in place and the float is not taking on fuel. I pulled the choke out and had a look and everything seems as it should be. Is there something that I might miss? I have gone over the carb and can't see anything wrong - so I thought I'd see if anybody else has been through this one.

Thanks

I had a problem with the choke piston failing to seal properly. A sympton of this was that I could lean off the mixture screw all the way and the cylinder would still run (in fact it ran better!) as fuel was being delivered by the enricher circuit. I cleaned out the choke void with a wooden dowell and very fine wet and dry abrasive paper - same treatment to the choke piston - that solved the problem.

The choke plunger has a rubber seal on the bottom that goes hard and develops an imprint,they can be pryed out and reinstalled,or replace the whole plunger

Yep. That problem too. My rubber seal was fine. The plunger was hanging up in the void due a combination of a small burr on the sharp edge and some gunk on the piston. It certainly doesn't hurt to carefully prise out the rubber seal and turn it over. Having said that, i subsequently bought a new pair of plungers for $10 Aussie for the pair. (Apparently you cant buy just the rubber seal)

Aha! That sounds right. I took the choke piston out and saw that imprint in the rubber. Also the rubber still seems pliable. I will try turning it over and if that doesn't work then I'll just get a new piston. Thanks as I thought people would tell me to check the float and so on - which I did.

Many thanks and I will report back once it stops raining...

One other obvious thing to check - make sure you have enough choke cable free play at the cable adjuster to allow the piston to sit down properly. (assuming you have choke cables and not levers installed)