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MG Midget and Sprite Technical - Carburettor Piston

Stupidly, whilst overhauling my carbs (twin HS2)recently, I dropped the piston onto a concrete floor. It resulted in a slight flat spot (and two corresponding slight high spots) on the side of the piston, and has knocked it out of a true circular shape. It now doesn't move at all freely in the dashpot. I have tried some very gentle wet and dry, to make it fit, but I don't think it's ever going to be a very good fit. I am thinking of buying a second hand carb (they seem to sell quite cheaply on ebay) and just using the piston and dashpot as a replacement. I understand the piston and dashpot are normally 'paired' together. My question is, would there be any problems in fitting the piston/dashpot off another carb? Presumably I would have to make sure it's off an HS2? Is there any difference between a single HS2 and a twin HS2 as far as the dashpot/piston are concerned? Or does anyone have one for sale? Any advice appreciated.
Jonathan 1972 1275 RWA

I could probably give you one if I have a route around over the weekend

I live near Scunny where abouts are you mate?
Robert (Bob) Midget Turbo

You'll want to test any replacement piston/dashpot to make sure its damping rate is similar to that of your other carb.

Cheers,

-:G:-
Gryf Ketcherside

Also take care that the oil dampers have the same free play ie the same number. And that both dashpots have the same vent to ambient air, both through an internal bore or via the hole in the oil damper.
Otherwise no problem.
Alex G Matla

Hi. Thanks for your replies.
Bob. I'm in Cherry Burton, near Beverley. If you fancy a run over, that would be great. What do you reckon? I'm happy to pay/barter! Could you let me know? My email is jrmiddleton (at) supanet (dot) com

Gryf/Alex - that's what I wasn't sure about. I hadn't appreciated the oil dampers might vary. I'll check that. I can keep the same spring and the same needle so, if the replacement is in reasonable condition I imagine it would work the same?
Jonathan 1972 1275 RWA

If you're stuck I think I've got a set you can have but I'd have to check which ones they are as they were given to me just for (careful now!) one screw and later one float needle to replace one of the new I bought that still allowed floading
Nigel Atkins

Well, I polished up the edge of the piston a bit more so that it seemed to run freely, and reassembled. Engine started up fine and seems to run ok.

I did notice that despite running freely, the piston seemed to have a lot more damping than the other (if lifted it took a lot longer to fall back into position). Looked at the internal springs, and they seem to be different - one is slightly longer and thicker gauge.

I know they are meant to be marked red or blue but I couldn't see any sign to indicate what they were. Anyway I swopped them around, to balance out the unevenness in the pistons, and all seems well.

Not sure it's meant to be like this but if it works I think I'll leave well alone and see how it runs.
Jonathan 1972 1275 RWA


something to watch out for is the needle in the piston, those things like to stick like super glue and the brass pin likes to snap off at the base of the piston... so work it gently with lots of aceton and PB breaker over several days... it will come out, but it takes some doing


If you have the little stamped triangle piece that holds the part number on the float chamber

Id be strongly tempted to just buying the exact same part number carb and using it and the other as parts... you can never have enough carb parts...LOL

if you do find another carb for parts... make sure its off a good running car... these things crode really nasty like all get out if left to set for several years without use
Prop

This thread was discussed between 10/03/2011 and 12/03/2011

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