Author Topic: 1953 Plunger A7 carburettor leak  (Read 604 times)

Offline k0337788

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1953 Plunger A7 carburettor leak
« on: 09.08. 2023 08:33 »
Hi all, I have a 1953 A7 Plunger that has fuel leaking from the cutaway as shown in the attached image. The bike runs fine but if you stop it without turning off the fuel it has a fuel leak. I have stripped the float bowl & It is sitting in the groove on the needle & the float does not have fuel in it. Any ideas on a cure? Thanks Andy 

Offline Swarfcut

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Re: 1953 Plunger A7 carburettor leak
« Reply #1 on: 09.08. 2023 09:52 »
   Looks like a 276 carb with remote float bowl. The thickness of fibre washer between the base of the jet block nut and the top of the float bowl mounting alters the height of the  float bowl relative to the fuel level to the top of the needle jet. Bowl too high, fuel will overflow. Looks like the washer is too thin or missing.

 Swarfy.

Online Angus

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Re: 1953 Plunger A7 carburettor leak
« Reply #2 on: 10.08. 2023 07:37 »
I have a 276 on the Norton Model 7 and it has always leaked. tried everything, more washers less washers new float & needles. It leaks when I tickle it, which I have to do to start her, so I start her quickly and it stops. It leaks if I dont turn off the tap before killing the engine if I put her on the side stand (which changes the height of the bowl). Eventually one of the older club members told me they all do that they are know as old leakies  *sad2*
1961 A7 since 1976, 1960 A10 Gold Flash Super Profile Bike
1958 Matchless G80 Project, 1952 Norton Model 7 Plunger
1950 Triumph T100, 1981 Ducati Pantah 500, 1959 AJS model 20

Offline k0337788

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Re: 1953 Plunger A7 carburettor leak
« Reply #3 on: 10.08. 2023 08:09 »
Thanks Guys - looks like its a common problem - Ill try gaskets first. I bought a new 276 remote bowl carb from Amal for my 47 A7 rigid & this does not have the same problem. Interesting symptoms from Angus exactly the same as mine!! Maybe we should seek counselling!

Offline k0337788

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Re: 1953 Plunger A7 carburettor leak
« Reply #4 on: 10.08. 2023 08:21 »
Swarfcut - before I have a go at altering the float bowl height - is it the fibre washer at the top of the float bowl banjo that needs to be thicker thus lowering the float bowl Thanks Andy

Online groily

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Re: 1953 Plunger A7 carburettor leak
« Reply #5 on: 10.08. 2023 08:45 »
  . . and it has always leaked. Tried everything  . . . told me they all do that they are known as old leakies  *sad2*
Yup, had the same with a 76 on one of my machine's Angus, and that a recon'd one at vast expense. I've passed it on to a guy with a similar machine who is more bothered about 'original' than I am.  Exact same thing with a mate's early 5T trihard, where drips are tolerated in the interests of 'correct'.

The short (but heretical) answer for long-term leak-free on a 'rider' rather than a show pony is "Fit a Monobloc" if the space allows.
Bill

Online chaterlea25

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Re: 1953 Plunger A7 carburettor leak
« Reply #6 on: 10.08. 2023 14:00 »
Hi KO,
You can check the fuel height on most 276 carbs easily if there is a 2BA screw in the banjo at the base of the float chamber
Stick a small bore plastic tube in there
And bring it up the side of the carb
The level should be to the bottom of the pilot air screw hole.
The place where the fuel is leaking is an air inlet and need to be clear.
The 276 and similar carbs will "leak" there
If the carb is tickeled no matter what you do..
A poor design and a fire hazard

John
1961 Super Rocket
1963 RGS (ongoing)

Online Rex

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Re: 1953 Plunger A7 carburettor leak
« Reply #7 on: 10.08. 2023 16:28 »
They normally drip/leak if someone has tried to lap in the float needle and ballsed it up forever.
Always turn off the juice when the engine is stopped, and the consolation is that they rarely leak when the engine is running.

Offline k0337788

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Re: 1953 Plunger A7 carburettor leak
« Reply #8 on: 12.08. 2023 09:47 »
Chaterlea great tip with the plastic pipe - Ill try that

Offline 7iain7

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Re: 1953 Plunger A7 carburettor leak
« Reply #9 on: 12.08. 2023 18:06 »
The 276 on my plunger would leak, sometimes more than others. The fire hazard issue worried me. So, first I changed it for a PWK, which it ran really well on, but had hot-starting issues. It now has a Wassel 928 fitted.

Personally would look into a 600/26 or a 26mm PWK

52 A10

Offline Minto

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Re: 1953 Plunger A7 carburettor leak
« Reply #10 on: 12.08. 2023 23:54 »
 My 52 plunger A10 has a 276 pre monobloc also, mine only leaks if I over tickle it. Even on the side stand with the fuel (absent mindedly) left on, no leak. Plenty of other problems but not leaking. How can this be? Well, I rewelded my snapped off side stand lug back on so that the bike sits much more upright!
Yes, it used haemorrhage fuel from above the jet block nut when on the side stand, like they all do.
52 A10 plunger
Aprilia RSVR