Mk1 Concentric real problem

[leobailey]

My 1959 G3 ran reasonably well on my old 376/5 Monobloc, true I'd previously had some problems over difficult starting but a major AMAL repair kit seemed get over those.

Now for my problem. I decided it may run even better on a new carburettor, and accordingly I purchased a brand new Amal Concentric Mk1 28mm from Hitchcocks Motorcycles.

The bike certainly seemed to start a little easier, and ran much as with the Monobloc. However the bike intermittently floods after starting. I can start it on the centre stand and all fine for a moment or two, but 1 in every 3 times it then starts to flood petrol out of every orifice even when the bike is running.

I'm fed up of pulling it down and checking float height, but still can't find what's causing the problem. I've had the bowl assembly set up on the bench with a petrol supply and it works fine at shutting off. Stick it back on the carb on the bike and here we go again, flooding .

There is quite a bit of internet advice on how to set the fuel level on a concentric, does anyone have the definitive answer ?
Some say you set the fuel level 4 to 6mm( below the bowl top while others tell you that the top of the float should be 4 to 6 mm below the bowl top.

HELP
Leo

[Mick D]

Hi Leo

My first action would be to seek a replacement carb as yours seems to be faulty from manufacture.

I refurbished three Mk 1 concentrics last year as part of a T160 restoration and the only thing that springs to mind is the float is getting stuck intermittently. This can happen if the float bowl gasket is fouling the float - check especially the areas of potential conflict pictured:

Concentric Float.png

The pivot pin should not be corroded in a new carb but check when it's apart and also check the pivot holes in the float don't have bits of rough plastic hindering it's motion.

Regards Mick

[Andy51]

Hi Leo, I had exactly the same problem, and the gasket was at fault, nipping the float pivot pin at each end. As Mick says, just snip off a bit of the gasket where the arrows point in his diagram, and all should be well. Andy

[Richard Mills]

Hi Leo, I had exactly the same problem, and the gasket was at fault, nipping the float pivot pin at each end. As Mick says, just snip off a bit of the gasket where the arrows point in his diagram, and all should be well. Andy

Ditto

[ajscomboman]

I ditched a concentric exactly for the problems reported. I trimmed the gasket around the pivot pin, polished the pin to ensure it wasn't sticking and it still pissed out the tickler every 3rd or 4th time of use. Went back to a monobloc, happy days.