AMAL Bowl Drain Plugs

I've read some posts here about AMAL Concentric carbs losing their drain plugs and I've been working with AMAL lately on several drain plug issues.

First, I've always tightened them with a US quarter dollar coin and have never had a problem until recently. This includes the plastic and metal plugs.

Second, A few weeks ago a put a new Premier set on a Trident. One plug leaked like a sieve no matter how tight I made it, one leaked a little and the other was fine. On investigating I realized that the old thick washer had been replaced by thin hard fiber by AMAL.

When I spoke with AMAL, they said that the Zinc bowls were not machined flat on the bottom, but the aluminum ones were, and they thought they could quit using the old soft thick washers. They wanted to change because they were getting a lot of complaints from people who were overtightening the plug and cracking the washer which made it leak right away or worse come out while riding. Of course, the hard fiber needs to be much tighter, or they will leak or come out! To top that off, the one that leaked like a sieve was machined perfectly flat and exactly parallel to the bowl top, but the threads were cut at a slight angle so the plug could not seal!

Third, AMAL is about to switch back to a thick, softer washer but one that is tougher. All the carbs I have received recently have the newer washers. I am hoping that AMAL will include tightening instructions in the future to put an end to this whole issue. As far a I know, right now, I'm the only one getting the new washers in the carb sets and I don't have a stock of the washers themselves yet.

Last, if you bought a set from me and they have a hard fiber bowl washer make sure it is tight and if it leaks, email me. I can't do much at the moment, but should be able to in a month or so.

In any case, this works well: https://a.co/d/5yyoegu and besides stopping leaks it further ensures that the plug does not come out on its own. In a way, this is like liquid Teflon tape and I use it on the inner chain case to engine bolts to prevent oil leaks from the engine into the inner primary.

Good discovery Greg! I was also wondering why we seem to see the issue so often now but didn’t in the past.

Good tip on that Permatex too, I’ve ordered some.

Had the same leak/seepage problem. Banjo washers solved it.
Mcmaster-Carr has tube sealing washers that also work well

Thanks Greg. Good info and tips.

You could try one of these, although costly they are multi purpose. You could drain your bowls, empty your tank, share some fuel with a friend who has a Hirider tank or whatever. A bit unsightly, but totally functional. https://www.fasteddyco.com/product-page/float-bowl-drain-valve-for-amal-carbs I believe the company was named after Fast Eddie over the pond. Looks like they run nylon washers.

Sounds like an application for Loctite 577. I use it when putting fuel taps into tanks, etc. It sets quickly.
Cheers

Your experience with the Zinc vs. Aluminum bowls and how machining and thread angles can affect sealing is a great insight. It’s unfortunate that even with perfect machining, slight thread misalignment can cause leaks. Hopefully, the new washers will address the issue more reliably, and it’s great that AMAL is responsive to feedback.

I have used rubber wrapped round the area with a jubilee/ worm drive clip when on a long journey to make sure it doesn’t unscrew.

I just did a drain plug modification so I don't use a standard drain plug, but the gasket issue is the same as a regular drain plug issue... I think I spent more than $75. already on square profile Buna-N rubber doughnut sealing washers which don't work because they just wrinkle when you torque them. I wondered about nylon washers working, but they are slippery so I worried about the drain plug unscrewing because of vibration and the low friction of the nylon. I spent money on a few different nylon/plastic washers too. None of them made it past the dry fitting stage to go on the actual carburetor on the bike with fuel in them...

Then, of course, because I had them already and they cost me nothing, I tried the stock fiber washers which sealed fine, did not deform or wrinkle when torquing, and had enough friction to them that I felt like the new drain plug mechanism wouldn't loosen up from vibration. As usual, I spent money for nothing (without getting any chicks for free )

If anyone has a better option than the fiber washer, I'd like to hear about it. Even though I've had the new set up for a few days and it doesn't drip a single drop out the drain or the bowl gaskets (both being fiber washers...

*******I did think about the silicone impregnated gaskets that Jim Schmidt sells for valve covers and engine assembly and thought that might be a good product for carb bowl and drain plug gaskets... With the exception that the drain plug doesn't just compress the gasket, it also applies a twisting force to it while being tightened which the rest of the silicone impregnated gaskets don't have to endure... Anyone care to venture a guess on that?

I drilled the plugs and connected them together with a spring.