VB leaking petrol

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MarkOgden
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VB leaking petrol

Postby MarkOgden » Mon Jan 11, 2021 9:16 pm

Gents

Finally managed to start the VB after a long lay up. Went well for about 5 minutes then started leaking petrol. Not entirely certain where, but it looks like the overflow from the mixture chamber. Carb - Amal 276 - was removed and the brass float needle "cone" does look a little scored. Not sure why, never leaked before.....

Qs please

If I clean up the float seat and the needle (and possibly polish with T-cut?), I assume a reasonable test would be to fill with water/petrol and check the valve. Or are we talking new needle?

Fibre washers look brittle - especially the ones mating the float chamber to the carb body. I'll replace them - or is there anything better- and Is sealant or jointing compound advised here?

Anywhere else the leak could be? - petrol pipe unions look fine by the by.

Very many thanks

MarkOgden
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Re: VB leaking petrol

Postby MarkOgden » Mon Jan 11, 2021 9:34 pm

Supplementary question please - Amal 276 is a pre-monoblock. I have purchased a fibre washer kit - link below

https://www.ebay.co.uk/itm/Gasket-washe ... 57872.m274

Not 100% sure where the 4 smaller washers go - advice welcome

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simon.holyfield
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Re: VB leaking petrol

Postby simon.holyfield » Mon Jan 11, 2021 10:53 pm

Couple of thoughts. The float needle seat will work with a new needle, new seat or both, but the design is not as reliable as a monobloc.

Secondly, I've fitted a Dowty washer above the float chamber connection, with a new fibre washer below. There's not enough length in the thread for two Dowty washers.

IMG_20201127_122432.jpg


You can see by my fuel level that the float needle is not sealing well.

Make sure that you have a new fibre washer under the jet block, retained by the big brass fitting on the bottom, and that your float does actually float and that it is fitted in the slot on the needle. I've started using a tiny e clip in this slot, because my bow clip is not brilliant and sometimes it will drop the needle...
cheers

Simes

'51 Square Four,
'58 Huntmaster,
'42 W/NG,
'30 Model A
http://ariel-square-four.blogspot.com

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alan.moore
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Re: VB leaking petrol

Postby alan.moore » Mon Jan 11, 2021 11:25 pm

Mark
Does this help....276 parts diagram on Hitchcocks website
https://www.hitchcocksmotorcycles.com/p ... pages/3379

Re the leak...if petrol is coming out of the notch in the body just above the union nut as you say that's the overflow.

The needle seat is part of the float bowl...I don't think you can get a replacement seat. You can try lapping the cone of the needle into the seat with some autosol but go gently as its only brass and try to keep the needle upright/central or you will lap an oval into the seat.

Is yours a bottom feed like the one in the diagram? If so as you say you can take the float chamber top off and check the needle valve is sealing...attach the fuel pipe and turn the petrol on. Float should rise and then the valve should seal.

Make sure the clip that fits on the needle above the float has not come out of its groove and is a tight fit.

Make sure the 'tickler' is not sticking down slightly.

Re fitting thicker/ dowety washers to the float chamber connection remember that altering the height of the float chamber relative to the carb body also alters the fuel height.

Because the float chamber connection is at an angle you can rotate the float chamber fowards/backwards which also slightly lowers/highers the float chamber, again altering the fuel level.

Best of luck.
If you do a google search on amal 276 float needle seat forum there is loads of info on the subject

Cheers
Alan
1939 VH Redhunter;1942 RN WNG;1951 Triumph 6T Thunderbird;1970 BSA B175 Bantam;1986 Yamaha SRX600 single
http://cloggymoore.wix.com/triumph-pre-unit-6t

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alan.moore
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Re: VB leaking petrol

Postby alan.moore » Mon Jan 11, 2021 11:36 pm

Simon
That fuel level looks close to OK to me, would possibly be a bit lower without that air bubble in the pipe?
My understanding is that it should be just below the centre of the pilot aircrew.
On my WNG I ended up filing another slot in the float needle as I could not get the level low enough.... even with a new needle and plastic float from Burlen. If you get the level too low I found mine would spit back through the carb when you blipped the throttle.
Cheers
Alan
1939 VH Redhunter;1942 RN WNG;1951 Triumph 6T Thunderbird;1970 BSA B175 Bantam;1986 Yamaha SRX600 single
http://cloggymoore.wix.com/triumph-pre-unit-6t

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simon.holyfield
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Re: VB leaking petrol

Postby simon.holyfield » Tue Jan 12, 2021 8:35 am

It's the only picture I had Alan, and yes you're right, it's OK without the bubble.

I've repaired the needle seat in the float bowl, which was very worn, with a thin brass disc pressed in with a loctite sealant.
cheers

Simes

'51 Square Four,
'58 Huntmaster,
'42 W/NG,
'30 Model A
http://ariel-square-four.blogspot.com

MarkOgden
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Re: VB leaking petrol

Postby MarkOgden » Tue Jan 12, 2021 8:44 am

Gents

This is all useful stuff - very many thanks. Not 100% certain if it is the overflow, but I will try and clean up the needle and seat and possibly lap it in as you say.

MarkOgden
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Re: VB leaking petrol

Postby MarkOgden » Tue Jan 12, 2021 9:19 am

Just as an aside - what is the procedure for tickling when starting from cold - and how do you know if petrol is entering the carb prior to starting.

Do you tickle just before kicking over to find TDC - or just beyond - or tickle just prior to kicking over to start?

Mine seems to be a really bad starter, and I think it is fuel related somehow....

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simon.holyfield
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Re: VB leaking petrol

Postby simon.holyfield » Tue Jan 12, 2021 10:54 am

My W/NG is very sensitive to flooding and is a pig to start if I've overdone it - or was, I've done a lot of carburettor work since the last lockdown started and not had much time on it.

I give it the briefest tickle - it doesn't seem to matter when I do it during the starting process. You can see that the fuel is there by looking through the bell mouth - it looks distinctly wet.

Have you had a look at the pilot drillings in the jet block?
cheers

Simes

'51 Square Four,
'58 Huntmaster,
'42 W/NG,
'30 Model A
http://ariel-square-four.blogspot.com

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chris.shearwood
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Re: VB leaking petrol

Postby chris.shearwood » Tue Jan 12, 2021 1:03 pm

Mark,
You could always do what a previous owner did on the 289 of my VH: plug the overflow hole with a wooden peg! Yikes!
1946 4G, 1950 NG and 1951 VH


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