21 replies to this topic

[tiger99]

The official lapping compound for needle valves, and other things, is "crocus powder", but I have never been able to find any. Maybe you get it from jewellers? Anyway, many types of toothpaste do contain a fine abrasive, exactly what you want. I would never have thought about it, but it does make perfect sense. Something like valve grinding paste is much too coarse.

But every Mini "should" have acquired a viton-tipped needle many years ago, as the problem and its fix were common knowledge.

The needles sometimes still stick, either open or closed, and I have never been able to determine why, as inevitably they seem to be clean and freely moving. I guess that examination under a powerful magnifier would show some rough spots on the sides of the needle, or the body of the valve, so maybe a careful polishing of the sides would help. The forces involved are very small, pressure of maybe 3 psi over a very small area, and the buoyancy of a fairly small float, so it would not take much to cause problems.

One design of float tended to jam on its pivot pin, which is worth checking. Not sure if your carburettor has that type.

[dklawson]

Partially thread related text to follow:
Crocus is a term I haven't heard anyone use since my youth. You used to be able to buy Crocus Cloth which was like a sheet of Emory cloth but the abrasive was a very fine powder that looked like rust. Just try and ask a store clerk for that today and you will get nothing but a blank stare from them! A jeweler will have a similar material in the form of "jeweler's rouge". It is basically a fine red/rust colored powder that is used for polishing.

My Mini and my wife's GT6 see weekend use only and are not daily drivers. The Mini had problems with the float valves getting stuck closed while parked. I made a fix that others may want to experiment with. Small engine carbs (like on a lawnmower or other yard equipment) often have a loop of wire connecting the float valve needle to the float. When the float falls the loop of wire pulls the needle down off its seat. The float valves in my Mini have a little "knob" on their bottom surface (like those shown in the picture linked below) so I made a wire loops around the knob then formed an oval of wire that wraps around the pivot arm of the float (I have the older floats with the metal arms). When the HS carb float falls it pulls the needle off its seat (just like in a lawnmower). I have not had any stuck float valves since fitting the wire loops.

[ado15]

You should never go near the float needle with lapping paste. The seat is 'square' edged and the needle has a lot of float to allow self centring.

To answer an earlier comment...
When you lift the lid off, the fuel will always be low. You have just removed the float which displaces a lot of fuel.

I had a new lid assembly (lid, float and needle valve) recently which overflowed. I couldn't get it to seal. I put an old float needle and seat in and it was fine. The new, viton tipped, needle looked fine, as did the seat. Never did get to the bottom of the problem.

[KernowCooper]

never get caught with a bag of Jewellers Rouge the police wont beleive you lol

[finch661]

i had the same issues on my twin carbs, i replaced the values with these => http://www.minispare...|Back to search
worked really well. My mg midget suffered a similar problem on one of the carbs, and the valve was sealing fine, but the fuel hose clip just wasnt sealing the pipe (even though it was tight. might be worth checking that you are using proper fuel clips (i.e not jubilee clips)

[A-Cell]

Plenty of crocus powder available to you all. It's ferrous oxide i.e.RUST! Used as jewellers rouge for polishing. The cloth you mention doug was used for finely honing woodworking chisels. I guess it wa calle that because it looked like saffron. Bit a difference in price though!

[dklawson]

i had the same issues on my twin carbs, i replaced the values with these => http://www.minispare...|Back to search

The jet shown in the link is also known as a "Grose Jet" (which is a brand name). They have mixed reviews. I am glad you had good luck with them. I have not. I tried and removed them in both my Mini and my GT6. One set had the habit of sticking closed, the other never sealing. Be advised if you want to try these that the "new" ones are reported to ship with a rust preventative coating on the sealing ball(s). Fuel sometimes does not wash this off. Stories from other forums advise washing the jet assembly (in and out) with spray carb cleaner to remove the coating so the jet will seal properly. Regardless, if you do fit this type of jet, keep an eye on them.

ADO15, the lapping with toothpaste or rouge is not intended to do anything more than remove any burrs that are preventing sealing. That is why such a fine abrasive was suggested. I believe Tiger pointed out that normal lapping compound would be much too coarse.