AJS & Matchless Owners Club

Hi!
I was rebuilding a 276 carb the other night and noticed something odd about the brand new float that I was installing. The float height seems to be about 3-4mm higher with the new float compared to the old one... I tested it with a piece of clear tubing attached to the float bowl drain hole, water flowing in through the bottom feed, and with the needle of the new float set to produce lowest float height (seemed to correspond perfectly to the position of the needle on the old float). The locking clip of the old float could have been manipulated by a previous owner. I should have posted pictures of this. Will do so later on...

I was having trouble before with an spontaneously overflowing carb. I did find two small holes in the old copper float (bad solder joint). I fixed those with some solder, but the overflowing did not stop. It seems OK once the engine is running, and only happens sometimes during starting. Thought this could be cured with a new float...

Anyone noticed this about the float height before?

arcturus wrote:The float height seems to be about 3-4mm higher with the new float compared to the old one... I tested it with a piece of clear tubing attached to the float bowl drain hole, water flowing in through the bottom feed,........

If I understand correctly you tested it with water????
Perhaps the greater density of water vs petrol made it float higher in the water than it would in petrol.........?

Adding solder to seal the holes of the old copper float would increase its weight, making it float lower in petrol..........?

SPRIDDLER wrote:If I understand correctly you tested it with water????
Perhaps the greater density of water vs petrol made it float higher in the water than it would in petrol.........?

Yeah, but the float height should not differ much between two different floats when both are tested in water... I did a quick test as I was cleaning out the carb with soap and water. That's less messy than testing with petrol. It's going through a complete cleanup and rebuild anyway...

Trying to pinpoint faults on a carb is not easy without sight of the unit.
Assuming that the old needle is compatible with the new float maybe you'll have to create a new groove for the clip in the needle to achieve the required fuel height.
If the new float is floating 3 to 4 mm higher than the old float is it possible the top of the float is hitting the tickler before it has lifted the needle sufficiently to shut off the petrol supply?

Took some photos today. Hard to tell from the photos but the conical part of the needle (the part that counts) is placed at exactly the same distance from the bottom on both floats. It just seems like the new float has a lower buoyancy which leads to a higher float level... The new plastic float IS heavier than the old by a few grams according to my kitchen scale. I keep expecting the new parts I buy for my bike to be usable... Very often I end up fixing the old part since that is way better... This an Amal original spare part by the way.

Does the clip mount of the old float look ok to you all? The bends look un-tampered, or?

Hi

That old float looks wonderful to me, I'd be doing all I could to keep it installed. Looking at your last photo the sealing cone of the valve seems to have surface marking / damage, this coupled with associated damage to the brass valve seat, may well be responsible for the leak when static. I'd replace the needle and it's seat and see how new items perform.

Regards Mick

Hi Arcturus

When the carb leaked before was the leak from the top of the float chamber or the jet block on the carb?
If it was from the top of the float chamber then it may be worth trying to reseat the fuel valve with a little Solvol Autosol or other fine polishing paste and spin the needle in the seat. If this does not solve it then follow Sprid's advice and make another groove a little lower than the existing one to lower the float and shut the fuel off earlier.
It was probably leaking from the jet block too and fine adjustment can be made by fitting an extra fibre washer under the float bowl mounting thus lowering the fuel level in relation to the jet block.
Worked for me.

Jim

JimFitz wrote:Hi Arcturus

When the carb leaked before was the leak from the top of the float chamber or the jet block on the carb?
If it was from the top of the float chamber then it may be worth trying to reseat the fuel valve with a little Solvol Autosol or other fine polishing paste and spin the needle in the seat. If this does not solve it then follow Sprid's advice and make another groove a little lower than the existing one to lower the float and shut the fuel off earlier.
It was probably leaking from the jet block too and fine adjustment can be made by fitting an extra fibre washer under the float bowl mounting thus lowering the fuel level in relation to the jet block.
Worked for me.

Jim

It was leaking (or more like flowing freely) from the four vent holes in the carb body. I really like the idea of fine tuning float level using fibre washers. I had not thought of this before... Thanks!

And yes, I might look into using the old float. It seems better an many ways. It's lighter than the new one. The needle is made of brass (same as the seat) while the new needle seems to be steel. I don't know how this would affect wear of the seat...

I have not yet seen a reproduction part live up to the quality of the old parts. They are often made of different materials, old parts were hardened - new part isn't, and they generally fit badly...

Amal only sell their nylon float with a new needle because they are aware that it has different characteristics to the old copper floats. Their needle has two slots in it, one marked "P" for plastic and the other marked "C" for use with the original copper floats. If you use a new float with an original needle your fuel level will not be correct. You can see the needle required on their website here: http://amalcarb.co.uk/pre-monobloc/76-2 ... -feed.html

I used the new needle with the new float. Also, the clip was in the most beneficial groove to get the float level as close as possible to the old float. To get the level right I will need to cut a new groove in the needle, which I'd rather not do. I'll have to check the needle again, but I really don't think this is usable...