Loosing revs and power

[Nitti]

Hi guys,
Its been a while , but both the bike and I are doing well.

Today's question :

While revving my A10-53, both when driving (in 1st and 2nd gears) and in stand-still,  it looses power and flats out !
No miss-firing though, but increased smoking from the exhausts.
I do not have a rev-counter on it , so it is difficult to give you a precise figure when it occurs !

To me this indicates that the carb is OK, and the problem is either in the ignition or the valves, what do you think ?

It could also be that I stretch it, what is the max revs normally before the A10 chokes ?

I have no problems starting it , and it works perfectly in the rest of the rev-band !

Happy midsummer
Nitti

[a10 gf]

Initially, 1st things I'd have looked at, the autoadvance (if you have one) not moving freely, or the carb at low to mid throttle opening.
e

[Nitti]

Hi e  & thanks for the reply
yes I have an autoadvance, how can I check it, just by feeling that it is moving, or visually by revving the engine while looking at it ?
Concerning the throttle, the engine "stalls" at rather high revs, I guess 1/2 to 3/4 throttle opening, would that mean that I should lift the needle one notch you think.
I have not checked the plugs, but if they are "whitish" at the mentioned throttle-opening that would indicate a weak mixture , wouldn't it ? But would the engine stall due to that without any spitting ?

Wahat about valve-clearance, could stalling occur due to this, too lare  or too tight settings ?

Nitti

[a10 gf]

but increased smoking from the exhausts

black, I suppose, not blue. Yes, check the plugs after running it for a while in the 'difficult' rpm area. Soemone else here may have suggestions about the autoadvance.

If nothing obvious appears, this may be an elimination-method job.

[Triton Thrasher]

Is the air slide (choke) fully open?

[BSA_54A10]

Take the bike for a run and when it starts to play up remove the filler cap.
If the problem goes away then you have a blocked cap vent.
If it gets better bit not gone all together then  have a good look at the filter in the banjo and the fuel taps.

If you have a choke ( air slide to some) pull it on ( choke the cards) a little, if it gets better then you still have a fuel supply problem .
If it gets worse then it is not a fuel supply problem.

If no difference then you need to get your hands on a colour tune other wise you are just proverbilally "pissing into the wind with your eyes closed"

Next make your self a couple of "special tools"
One is a can that will hold about 2 liters with provision or hanging it up. Cut a hole in the bottom and fix a spiggot in there big enough to take a lump of fuel line long enough to go from the cloths line ( or other suitable hanging point) to your carb ( I use a Bantam tank or some times a lawn mower tank)
Next tool is a piece of tube with a slot cut down its length so that it will slip over the rear brake rod / cable and long enough to cause reasonable brakeing force to be applied to the rear drum.

Now go for a ride, get the engine nice and warm, pop home slip off the petrol tank, pop in the brake tool and the colour tune. Start the bike and run it into the "trouble zone".
Look at the mirror of the colour tune.
Nothing at all = no spark, look at the ignition.
yellow flashes then nothing, look at the ignition
Flashes some times blue, some times yellow fuel blockage / air leak
blue flashes fadeing to white, then only a spark, fuel blockage / air leak
Blue flashes turning yellow then nothing too rich.