Author Topic: Flooding Amals  (Read 5400 times)

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Offline Alex Hall

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Flooding Amals
« on: 22 Jul 2008 at 10:06 »
Hi All. Can the needles  be re bedded in to the valve to make a good seal? Grinding paste or metal polish? Is it a successful result usually? Or would it be better to replace needle valve and seating? 

Offline eddie

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Re: Flooding Amals
« Reply #1 on: 22 Jul 2008 at 11:40 »
Alex,
         Firstly, check the holes in the bottom of the float chamber that guide the bottoms of the needles. They sometimes get blocked with sediment, then the needles drag on it - or worse - get pushed off centre. Only try reseating the needles if there is a definite step on the taper. Remember this will result in a rise of the fuel level - not over important on a single carb, but, ideally twin carbs should be an identical pair.
                                Regards,
                                              Eddie.

Offline Alex Hall

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Re: Flooding Amals
« Reply #2 on: 22 Jul 2008 at 13:45 »
Thanks Eddie, have you tried using polish on the needle? There is a distinct step in one of them!

Offline eddie

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Re: Flooding Amals
« Reply #3 on: 22 Jul 2008 at 17:12 »
Alex, You have headed this topic 'Amals Flooding' - do you mean that petrol is literally pouring from the float chambers or does the level rise slowly until fuel drips from the carbs? If it is pouring out, then the problem is probably not the poor seat on the needle. If it is, the seat will be so bad that replacement will be the only remedy. Take the lid off the float chamber - invert it and place the float and needle assy into it - check that the float does not contact the tickler button - this could be holding the needle off the seat. Also make sure there is no muck in the needle seat - I have seen carbs with the petrol pipe fitting full of debris from the petrol tank! With regard to lapping in the needle and seat - the step in the taper on the needle will only be made worse by trying to lap it in - a better solution would be to get someone with a watchmakers lathe to re-machine the taper - that is, if new needles cannot be obtained. In any case, I would only lightly lap the needles with Solvol Autosol.
                         Regards,
                                        Eddie.

Offline Alex Hall

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Re: Flooding Amals
« Reply #4 on: 23 Jul 2008 at 07:02 »
Hi Eddie, Yes the float bowl slowly fills up and fuel begins to pour from the two little overflow holes in the cap. Pulled them apart countless times and finally noticed that the needles had a distinct step in them. Rummaging through a bag of spares found a couple of other used needles with a better tip. BUT what became apparent was the material the old needles were made of was brass whilst the ones in the bag look like stainless! Lapped with autosol mixed with a miniscule amount of fine grinding paste, washed them out, then again with autosol only and they seem to have bedded in. I tested them by inverting the cap, placed the needle with float into it and blew as hard as possible . No leaks. Only when i took 9 bar of air pressure did it move! There was also some gunk which had grown or attached itself to the copper floats and I polished this off, hoping to get the floats to be more bouyant. Installed the whole shebang and no leaks at last. The MK4 fired up first time no throttle, no choke and full advance. Superb! Thanks Eddie. Wish you could have heard both cylinders firing at the same time finally and without standing in a pool of costly petrol. I even began to tweek the air screws which now made a difference. So onward we go, tweeking the carbs to remove the hesitancy when one opens the throttle, taking slack out of front brake cable which seems to be at the limit and when I pluck up courage tackle the jumping second gear. Thaks for your help

Offline eddie

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Re: Flooding Amals
« Reply #5 on: 23 Jul 2008 at 07:46 »
Alex, Regarding the 'hesitancy' as you open the throttle - I have always found that the Mark series machines pick up cleaner with a smaller slide cutaway (4 instead of 5). Since the change to unleaded petrol, this is even more noticeable. You may be able to trim a little off the bottom of the original slides - but make sure the slides don't then sit on the top of the choke blocks. 30 thou off the slide should make a difference - you may need to compensate by lowering the needle one notch.
                                     Regards,
                                             Eddie.

 

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