Carburettor flodding A10, monobloc 389

[Viking]

A10 fitted with a Amal monobloc 389 from 1996, used 30K.

When starting my BSA A10, I turn on the fuel taps, after a short while, the fuel is pouring out of the drain hole in the tickler pin, and it will not stop pouring out fuel before I turn off the fuel tap. 

Pressing down the tickler pin and realizing it, do not stop the flooding.

Starting the engine with the carb. now flooded, after approx. 10 sec. running, I can turn on the fuel supply and the float needle works fine.

I have cleaned the needle seating with carb cleaner etc., and changed the needle with a brand new needle from Amal, but it still do “the trick” of pouring out fuel until the engine vibrates the needle to close on the seat.

The carb is fitted on an alloy head, and is slant fitted, doo to the angle of the cast inlet manifold.


Any advice or tricks on stopping the flooding / pouring of fuel ?

Viking

[bsa-bill]

just a sideways look at things, it has been known for a fuel tap to leak and the fuel run down the feed pipe to the carb - I know this to be true - nuff said.
Worth checking out, cork would maybe swell a fuel passed over it then seal.

Otherwise it's down to needle (viton tipped?), and the bits and pieces around it

[Viking]

Good advice.

I gave up the Edward type “gas valve” on the bike.
Endless problems with the new type of fuel with 5% ethanol.
Constant leaks and problems.

I have fitted modern ¼” valves, and they works very well.
Like the old school valves, but after endless problems with cork, chancing cork and tried Viton rubber gaskets from Dragonfly. I gave in and fitted modern leak proof valves.

I have changed float needle to manufacture new unit, with Viton tip.
(Same as fitted in the carb from new in 1996)
But same result. Keep pouring out fuel until engine vibrations can close fuel supply with the float and needle valve.

A bit strange...

[bikerbob]

It is obvious that the needle for whatever reason is not sealing in it's seat properly, you could try removing the float bowl cover and using a screwdriver slowly lift up the float bowl and see if the needle actually slides up into the needle seating easily and it is not slipping to one side and jamming thus when you start it up the vibration moves the needle into place. Have a look at where the base of the needle seats on the float and see if there is any marks that allow the needle move to one side and jam.

[The Artful Bodger]

I had the same thing with my Bantam (375 mono block), floods out when the fuel is first turned on. Start the bike and it's fine there after. The float had swollen and was catching on one of the float cover bolt humps when the float dropped as the fuel evaporated.
  I filed a little away from the hump and all was well for a few weeks, then it started again. A replacement float solved the problem. I think this is yet again one of those "ethanol caused"problems!
Colin

[chaterlea25]

Hi,
A not unheard of problem,
Has the little spacer that goes on the pivot between the float and cover been lost?
"Flash" on the plastic moulding sometimes causes binding of the float

A couple of years ago while on holidays in France and Switzerland I had continuous problems with carb flooding on the Mikuni on my SR  it had not given problems before
On returning home I needed some petrol for the lawnmower so drained some from the SR, guess what? lawnmower carb started flooding too
Refilled with fuel bought locally and the problem dissapeared    WTF !!

John

[duTch]

 

Pressing down the tickler pin and realizing it, do not stop the flooding.

  I had a similar too, but can't remember what I did to fix- maybe let it spring up quickly (use your finger nail). I have a copper float and a spare plastic one...which did something different ..

  Does yours have a fibre washer under the tickler? If so, try it with that out..

[bobandbec]

I have this on a 1962 A65 star with the monobloc on.

I have discovered that the float can sometimes stick when it falls to the bottom of the float chamber. It sticks on the "rib" that goes across from the screw holding the float chamber cover on and happens when I run after turning the taps off so the chamber is low/empty.

The starting of the bike and the engine vibration etc is enough to free the float so the flooding stops.

I've bought one of the stay up floats to try in place of the original. Not fitted yet.

Peter

[KiwiGF]

Chatter lea's diagnosis would be my bet  those spacers are easily lost.

One way to help with the diagnosis on is to take off the float side cover and replace it with cling film and an elastic bag so you can see what's going on, it's a an advantage of the mono bloc over concentrics 

[beezermacc]

Make sure you do not have a fibre washer under the float needle housing.

[Viking]

The carb is fitted with the # 16 Needle seating washer and # 18 Float spindle bush.
Fitted with the modern “Stay up float” from the manufacture.

http://amalcarb.co.uk/carbspec/carburettor/spares/id/4776/

It was manufacture new in 1996. I used the bike in England until year 2000. Newer a problem. (with carb flooding).

After moving to Denmark in year 2000 it was ok until about year 2010.

Looking back: The issue with flooding arise about the same time as the introduction of 5% ethanol in petrol in Denmark.

Used the bike on a road trip to “Øland” in Sweeden last year. 1400 km in 3 days.  

Nice trip and super roads for 50HP BSA RGS Engine, but the high octane 100 fuel in Sweden gave problems with more flooding and it “killed” the Edwards pet.tank valves. The cork dried out and gave a nasty leak…
(It ran like a "Bat Out of Hell" on that fuel  ). Days of pinking was gone..

Pet tank valves changed to modern type, and stopped the problem.

Could be the float is sticking on the pivot pin, or the needle is not moving freely.
Good trick with the “cling film”    

Viking

[atkin]

 I had the problem when hot if I tickle the carb petrol would flow out . I fitted an updated stay up float no problem now .

[Radlan2]

I know this applies to concentrics whether it applies to monoblocs I dont know. There are three (or more?) types of float needle availiable original nylon, brass viton tipped and aluminium viton tipped. I fitted aluminium which were recomended as part of the stay up float/ethanol upgrade, they were prone to flooding so I reverted back to brass and I had no further problems. HTH
              Chris

[jjbsa]

I have had this flooding problem before on several bikes with Monoblocs 389s fitted with the AMAL "Stay up" plastic float.  It's caused by the float sticking in the down position when the carb is tickled.  The float can catch the casting when thje carb is tickled, holding the float in the down position.  The float catches in both old Monoblocs made by the original AMAL company and ones made by the new ersatz AMAL outfit.  Attached is a photo of one of these plastic floats catching the body of a Monobloc.  The carb is upside down and the float will not return. I now use only the old copper floats, which have a good clearance when fitted, and are immune to swelling from absorption of fuel constituents.
This is not the first time I have had problems with items from the new AMAL company.  A new Monobloc they supplied had an incorrectly machined mixing chamber body that would not seat on the main carb body because the bevel on its lower face was considerably too small.  I had bought this carb from a trusted UK supplier, who after he had investigated, told me that all their stock of Monoblocs of that size were also faulty.

[RogerSB]

Thanks for making us aware.
Rog.