BSA A10 suddenly running rich

baz

baz

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I fired up my A10 today after it had been standing for maybe 6 months or more
I drained the sump
Had to clean the points to get it to spark and it fired right up
But now it's running very rich and won't idle
Black smoke from the exhaust etc
The plugs are black
I took the pilot jet out and that was fine
Last time I rode it it was fine
Nothing has been changed???
There's no fuel leaking
 
Apologies for the 'Granny sucking eggs' here, Baz, but assuming the black smoke isn't oil related (yeah, white!!) then to be 'richer' the air/fuel ratio has changed?
Assuming (again... though we shouldn't) that there's no way more fuel has appeared, then less fresh air getting through, perhaps?
No mouse nest in the air filter? Cobwebs or other restrictions in the air supply?
 
It's black smoke
But it smells really rich like a choke being full on
There's no air filter fitted
No choke slide
I've just drained the tank of fuel bought fresh
I'll try that before stripping the carb
Just seems odd to me!
 
Filled it with fresh fuel
Made no difference
So I turned the fuel tap off and let it run
Just before it cut out it started running fine
So it's likely a float problem
 
I checked the whole carb
No loose jets
Needle was ok
I checked the float for leaks
Checked the needle valve and the pivot spacer
Absolutely nothing wrong that I could find
The only thing I would say is there was a very fine coating of powdery looking stuff inside the carb?
Anyway I cleaned the whole thing out and now it's running fine!!
I really don't know what caused it ?
I was expecting something wrong with the float or needle valve
 
If you cleaned the carb thoroughly whilst stripped that’ll rule out my hypothesis: gum or crap stopping the float needle from sealing fully…

the other thing I always think / say at times like this… new plugs…
 
Fast Eddie said:
If you cleaned the carb thoroughly whilst stripped that’ll rule out my hypothesis: gum or crap stopping the float needle from sealing fully…

the other thing I always think / say at times like this… new plugs…
Click to expand...
It's really puzzled me
I built this bike back in the 80s so I am very used to the things it does especially after I haven't run it for a while
I always have to clean the points
And drain the sump
But it always fires up and runs fine until this time !!!
 
baz said:
It's really puzzled me
I built this bike back in the 80s so I am very used to the things it does especially after I haven't run it for a while
I always have to clean the points
And drain the sump
But it always fires up and runs fine until this time !!!
Click to expand...


My A10 is heading towards the same thing. It only gets run a few times a year anymore and last trip out it was stumbling off idle and down on power a bit. All signs of a carb issue. Even worse is that after riding it I felt the difference between it and my Commando is like using a stone ax compared to a chain saw.
 
MikeG said:
My A10 is heading towards the same thing. It only gets run a few times a year anymore and last trip out it was stumbling off idle and down on power a bit. All signs of a carb issue. Even worse is that after riding it I felt the difference between it and my Commando is like using a stone ax compared to a chain saw.
Click to expand...
I've not ridden it yet but I will do soon
But it now sounds and runs really well
Yes there's a huge difference between one of these and a commando,it makes the commando feel like a turbine :D it brings me right down to grass roots motorcycling when I ride it
 

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