Solex carb leaks when bike on side stand

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Solex carb leaks when bike on side stand

Postby pauldridge » Sat Feb 23, 2019 8:35 pm

I've now logged 200 miles on my newly rebuild '53 Square 4 MK II, and it is all coming together.

One worrisome issue, however, is I've been noticing that after a good ride, with the engine heated up, if I put the bike on its side stand, I see petrol dripping from the carb. I can right the bike to level, and the leakage quits. Along with that, at all times, even if there is no leakage, I have observed that with the bike on its side stand, the idle speed decreases noticeably.

As near as I can determine from looking at parts explosions, inexplicably there seems to be no gasket between the fuel bowl and the carburetor.

I have completely disassembled the carb and run it through my hydrosonic cleaner, and insured all the jets are free. I see no evidence that the float has sprung a leak.. I've never heard any liquid inside when the float is out.

Some have suggested a shim washer underneath the needle valve, but I don't see any reference to that in the parts listing either.

Soliciting any opinions and suggestions.
Phil Auldridge Austin, Texas - USA
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53 SQ 4 MK II, '72 Norton Commando, '78 BMW R100/7, '79 Honda CBX, 2014 Indian Chief Vintage

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Re: Solex carb leaks when bike on side stand

Postby paul.jameson » Sat Feb 23, 2019 9:06 pm


Don't put the bike on the side stand whilst leaving the engine running. No, there isn't, and shouldn't be a gasket between the top of the float bowl and the main carb casting.

In my youth ( a year or two ago now) I worked extensively on platelayers trolleys on the North Yorkshire Moors Railway. These were powered by a 1325cc JAP V-twin engine designed by one Val Page. The carb was a Solex identical to the one fitted to the first 1000cc pushrod Squares and subsequently to the 600cc pushrod Squares.
The platelayers trolleys were thrashed without any mercy whatsover. We would use them to haul heavy loads of rails, sleepers, signals, etc. as we had no other means of moving such things at the time. Partial seizures were common and after a time, we began to find causes. The carb was mounted between the cylinders on a T shaped manifold held to the cylinders with large nuts round the manifold which compressed a tapered ring. Under severe thrashing and consequent high temperatures, the manifold had a tendency to droop on the tapered rings resulting in a carb out of level. This was enough to cause seizures through a weak mixture.
The Solex works fine if it is usually level - which it is as you sweep through left then right hand bends. Going uphill or downhill doesn't give the extent of variance from level which we got on the railway from "droop".

Hence the advice in my first paragraph.

Paul Jameson
36 4G, 37 VH, 54 KH(A), 75 Healey 1000/4, 52/53 ex ISDT KHA (project).
Former Machine Registrar & Archivist, General Secretary and Single Spares Organiser (over a 25 year period).
Now Archivist once more - but not Machine Registrar.

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Re: Solex carb leaks when bike on side stand

Postby simon.holyfield » Sun Feb 24, 2019 8:15 am

It's a brave man that uses that awful little sidestand.


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