Leaking flooding carb

[MikeCrook]

I have an amal 276 carb , I sent it away to be refurbished and cleaned as it leaked when engine not running.
It now leaks even when engine running. I dismantled the carb replaced fiber washers joint sealed the threads, still leaks .

I noticed the float hole has no seal where the needle passes through, will this not allow the flaoat to fill with fuel and stop it closing off the supply ?

Help please as it is preventing me riding the bike , 1936 NG 350.

Thanks

[Chris Sealy]

Hi Mike. The original metal float has an internal tube running top to bottom, soldered in place to seal it. To test it, simply put some warm water in a bowl and push it under. If you get a stream of small bubbles, the float is leaking and will not float at the correct level in the float chamber. Chris.

[will_curry]

Petrol should not leak out of the 4 holes is the body of the carb. If it is there
is an issue with the petrol level. Either the float is set up incorrectly or the
taper at the base of the float needle which acts as the petrol valve is not
seating properly. Any decent refurbisher should have checked both of these
before returning the carb to you.

If the petrol is leaking from anywhere else it is going to be a problem with the
mechanical sealing of the joint. I've never needed anything more than new
fibre washers to keep my carbs petrol-tight at the joints.

[SteveShone]

276 carbs are notorious for flooding. It's usually the taper on the bottom of the needle not seating properly due to muck or wear. I have found that grinding it in with fine valve grinding paste then finishing of with solvol (or jewellers rouge if you have any - it's cheap enough to buy) does the trick - same technique as grinding in a valve, just twist the needle back and forth whilst pulling it against the seat.
Float height is generally fixed - I've only seen them with one groove in the needle for the float clip to seat in. Its also worth checking that the top of the float needle isn't binding in the guide hole in the float bowl cap - unlikely, but you never know.
They can be a bugger of a carb but once sorted they are reliable enough.

Steve

[MikeCrook]

Thanks all, I suspect from what you say it's the tapered seat not sealing, all new parts fitted except the float, do the new needle and seat need grinding in ?
£200 cost of referb didn't even replace the fibre washers , one missing !

Thanks again for your help.

Mike

[SteveShone]

The seat itself is cast into the bottom of the float bowl so isnt really replaceable. I would expect that the seat would either need recutting with a specialised tapered reamer (though Im not aware of one) so if the seat is at all marked/worn then I would be grinding the new needle to ensure a seal - its easy enough to check per the last bit of this post.
One other thought - if youve had new corks fitted in the fuel taps, check for any fragments of cork that have broken away and is preventing the needle from sealing - that once caused me no end of aggro on my 49 Matchless It was a particularly poor batch of corks.

To check for the needle sealing properly, remove the fuel feed pipe (Im assuming its a bottom feed) and the float chamber cap, then while lifting the float up, top it up with petrol. If all is well there should be no torrent of fuel from the bottom. It may drip very very slightly but at no more than the rate needed to feed the engine at tickover Once the level drops and the float is no longer 'floating', then the remaing petrol will pour out. Of course it is easier with the float held in a vice on the bench, but still doable without fully dismantling the carb.

Good luck and persist with the 276 rather than fitting a later replacement Steve

[volker.halbach]

The original float chamber would have been top feed (fuel pipe connects to the lid of the float chamber), I think. Make sure the float is not held down by the tickler. The float level may be incorrect, because generations of previous owners lapped in the needle, stepped on the float on the floor etc. You can lower the level by fitting an extra fiber washer between the arm of the float chamber and the carb. Also swing the float chamber forward as far as possible.

[simon.holyfield]

I've replaced the float needle seat on the W/NG, to prove that I had a good seat in there and secondly to lower the float height a bit. I made a brass disc, 1 mm thick, with an interference fit to go in the base of the carburetter (mine is 1942 - a bottom feeder) with a hole for the needle, generating a new square edge for the seat. I pushed this in until it sat flat on the old seat with a bit of sealant (probably Loctite 1215). With advice from the club members, I lapped the needle in with Brasso and it now seals pretty well.

[MikeCrook]

Thanks again all, much appreciated the time you spent giving advice and sharing your expertise and experiences.
Should keep me busy waiting for the rain to stop in West Wales !

Mike