Ethanol and your Amal

Modern pump gas pulls water into your tank and leaves varnish where fuel should flow.

Your Amal Concentric was built for a fuel that hasn't existed since the Carter administration. Straight gasoline, no additives, and it could sit in the float bowl for weeks without becoming a problem. E10 doesn't work that way. It's a different chemical, and your carb is the part that pays for it.

Ethanol pulls water

Ethanol is hygroscopic, meaning it pulls moisture out of the air. In a sealed modern car tank that's minor. In a Triumph tank that vents, breathes, and then sits between rides, it adds up. Once the fuel absorbs enough water it hits saturation and separates. The ethanol and water drop to the bottom of the tank as their own layer, denser than the gas floating on top. That layer is exactly what your petcock feeds into the carb.

Leave E10 in a Triumph tank through a humid California winter and it will separate. It's only a question of when.

What it does inside the carb

Evaporation first. E10 gasses off differently than straight gas, and what it leaves behind is a sticky varnish that sets up inside the jets. A pilot jet with a .3mm orifice doesn't care about your excuses. It clogs.

Then there's the rubber and fiber. Old float needles, some gaskets, and certain bowl seals were never spec'd for alcohol content. Ethanol swells and degrades them over time, and a swollen float needle means fuel where it shouldn't be. That isn't a running problem, that's a fire under your seat.

You get about three good weeks

This is the number that actually matters. Fresh ethanol gas will run your bike well for roughly three weeks. After that the carb starts acting funny. Hesitation off idle, an idle that won't settle, a bike that just feels wrong in a way you can't point at. That's the fuel going off, not your tuning going out.

So stop filling the tank all the way. A full tank on a bike you ride twice a month is a tank of gas that will spoil before you burn it. Put in what you're actually going to use, pay attention to how fast you're going through it, and keep adding fresh gas as you go. New fuel going in on top of old fuel is the cheapest way there is to keep the average age of what's in your tank down.

Stabilizers

We have not found one that fully solves this. Some help, some don't seem to do much of anything, and none of them turn E10 back into 1968 gasoline. What they're mostly doing is slowing oxidation, keeping the fuel from going stale and gummy. That's worth something. It isn't the same as preventing phase separation, and the labels tend to blur that line.

Sta-Bil 360 is formulated with ethanol blends in mind. Star Tron works on a different principle, using enzymes to disperse small amounts of water back into suspension instead of letting it pool at the bottom. Both are worth a shot. Neither one buys you unlimited time, and neither one gets you out of the three week window.

What you don't need is four bottles of additive in your tank. Pick one, use it consistently, and pay attention to whether the bike actually runs better. Layering products doesn't stack up the protection, it just makes it impossible to tell what's doing anything.

Drain the bowls

When you know the bike is going to sit for a while, get the fuel out of the float bowls. That's where varnish does the most damage, because those are the smallest passages and the closest ones to the jets.

Easiest way to do it: on the way home, when you turn onto your street, shut the petcock off and leave the bike running. Let it starve itself out instead of hitting the kill switch. By the time it dies the bowls are empty and you never touched a drain screw.

Running the whole tank dry matters less than people think unless the bike is parked for months. The bowls are the part that counts.

Find better gas

California has more ethanol free pumps than most people expect. Check pure-gas.org before you assume you're stuck with E10. Marinas and small engine shops often carry non ethanol fuel too, since two stroke equipment has the same problem your Triumph does. It costs more per gallon. It's still cheaper than a carb rebuild.