Running rough, mpg down. Left hand cylinder has a light brown spark plug. Right hand is sooty. On the L/H choke, if I pull the outer cable awày from the carb. it snaps back by itself. The R/H one does not, also the brass piston is quite a tight fit in its bore, compared to the other one. Although on the R/H one, the cable seems to be very slack.
I am unsure how the choke actually works .Seems to me that the brass pistons should sit at the bottom of their bores, when the chokes are off.
There seems to be excessive slack on the offending choke cable, to me, I would have thought this would mean that the choke would not even operate.
The brass piston has a rubber seal fitted to its base which when its lowered to the bottom of its cylinder makes a seal, when lifted it allows more fuel into the carb.
Sounds like you need to either clean up the brass piston and barrel so it slides nicely or maybe get a new one.
You are right “choke” is the wrong term really, as does not restrict air intake it’s actually a ‘starting enrichment device’ comprising little “throttle slides” (the pistons) with the starter jets underneath, so as you say when off the piston needs to be fully down else excess fuel will keep coming out the starter jet. As said above there’s like a rubber button in the bottom to seal the top of the jet but gets indented over time so sealing ability can go off. New choke pistons should sort this (and come with new button inserts).
Ordered a new piston & return spring from Gutsibits today, got an e mail earlier, they’ve posted them already. I used an old scotchbrite kitchen pad to clean the piston, it is still sticky. Get a 8mm reamer from work tomorrow and run it down the bore, I can see some crap inside the bore.
Thanks for your replies guys. 3
I never felt happy that my cold start pistons were seating properly with the split cable system so I junked that and fitted the individual carb top levers.
I have considered this, but, dont think the R/H carb. would be accessible. Saw a le mans special at the Basingstoke transport show yesterday, only had a carb top mounted choke lever on one side!
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