Let’s get started on the work.
This unit has an unusually large amount of burrs. I’ll remove just the minimum necessary.
The plastic body shows heavy wear. I’ll remove the burrs from this area as well.
It’s already quite thin, but wear has reached its limit here, so we’re good.
The slide valve hasn’t worn much, which is good.
The BST has several different spring types. You can change them for tuning purposes—it’s an interesting carburettor.
I need to check just to be sure; if a different spring got mixed in, it’ll be a hassle later.
I check the needle valve for fit and rubber hardness. On a four-cylinder, it’s not a part you’d typically replace. I’d say overflow caused by a stepped needle valve is actually pretty rare.
Overflow is usually caused by rust or debris getting into the needle valve, gasoline going bad and sticking the needle valve pin, or float valve O-ring degradation—those are the most common culprits in my experience.
By running gasoline through and checking the actual fuel level, the condition becomes clear. Whether it rises slowly or overflows all at once, you can track down the cause in this state. Installing it on the bike without checking is risky.
Assembly is complete; now it’s time for synchronization.
Strangely, there’s barely any drift at all. Since it seemed lonely, I adjusted the sync screws a bit just for the sake of it.
Going back a bit: the starter valve. On the GSF and later, a washer is added, so I’ll follow the later-model design.
The time is getting awkward, so let’s take a service break.
It’s good manners to remove what can be removed.
Same here.
We went a bit out of the way, but I think it looks much better now.
Waiting for the test ride.
