Britbike forum Forums British motorcycles in general British motorcycles in general Concentric 928 stuck slide, long time sitting

Tried to get a BSA running today that’s been sitting for a year with no oil and drained tank. It’s been a battle, and it’s winning. The oil did go in the tank OK, so that’s about all that worked! Gas in the tank, of course the Ewarts corks drip, dried out. Decided to push it around to get oil moving, plugs out, grounded the plug wires, 3rd gear push, oil tank level did go down a bit, so good there. Tickle and kick, Boom Boom no accel? Twist group not moving, carb slide is stuck. Never had a slide freeze up from sitting inside a shop. Gonna be difficult to remove the carb when it comes to disconnecting the throttle cable.

Better in the shop then wide open throttle.
Body twisted? Or gummed up, or otherwise oxidized in there? I'm sure you tried the light tap with a plastic mallet

The design of Concentric carbs relies on fuel vapour being adsorbed into the oxide layer on both the slide & body to prevent them growing into each other thus causing the slide to stick
When they are left for very log times the fuel evaporates and any moisture in the air feeds the oxidization reaction between the metal & the air so the oxides grow into each other & youget a condition calles "Stiction"
When they finally part company, the weaker bond will break, usually takinga few atoms of the parent metal with it and you now have a condition called Gauling usually associated with metals that have a very tough oxide surface like stainless steel
Warming th e body with a HOT AIR GUN will usually free them up .

Thanks for that thought! I have a good heat gun to use, and surprised I didn’t think of that also! Carb is still on the motor, so will hope that works. Tomorrow’s a new day………….. 🛠

UPDATE: The heat did the trick! I tried to move it 1st thing just to see if the WD40 may have worked,… Nope, still stuck. Heat gun, 60 sec., it came un-stuck. It’s not rideable like this, but at least I can get it off the motor now!
Weird thing, this whole effort is focused on getting the dormant bike running, to test something. Once the slide was free, and I got the petcock corks working, I wanted to see if there was anything else amiss. So I did I start it, and it headed for 8,000 RPM! Fumbled for the key (one time it would be nice to have a kill switch!), shut it off. Glad I’d primed the oil system previously! Looked in the carb and I cannot see any gap under the slide but that has to be the issue. Backed off the idle screw just to see if the slide was down on it, it moved down so it was. Tried it again and same hi rev. Kind of bizarre, but carb coming off will show the cause I expect.

Probably a crank case full of petrol from the leaking tap ans an air leak around the carb flange

Gummed up slide and bore. I believe related to the stabilizer I have been using in the gas.

Most of the gunk thay you put in yout tank is just like the vitamin suplements peopl like to gobble up
They do very little apart from emptying your wallet unless you actually need them
In the case of fuel stabilizers 99% of the population do not need them but they get sucked in by the 1% who really do posting incrediable testimonials & case studies
Rather than putting goop in the tank better to empty it and tip the fuel into another vehicle or of less than 6 months fill the tank to the brim