Every March, the phone starts. The bike that ran fine in October. The varnished float bowl. The sticky throttle. The smell of old fuel that you cannot wash out of a garage. Almost all of it is the same problem, and the problem is what comes out of the pump.
California sells E10 by default. Ten percent ethanol mixed into the gasoline that goes into your tank. Fine for the modern fuel-injected bike in your neighbor’s garage. Often not fine for the carbureted twin in yours.
What ethanol actually does
Two things, mostly. The first is that ethanol is hygroscopic — it pulls water out of the air. After a few weeks in a vented gas cap, the fuel in your tank has water in it. When the water gets past a certain threshold, the mix splits. The water and ethanol drop to the bottom of the tank as one layer. The gasoline floats on top. This is phase separation, and the bottom layer is what your carbs are drawing from first.
The second thing is that ethanol is a mild solvent. Old rubber, old cork, old shellac — it attacks all of them. The float bowl gasket weeps. The needle valve tip swells. The varnish that years of unleaded gas left behind gets rinsed loose and lands in the pilot jet.
Amal carbs are particularly bad at handling this. Small passages, brass that interacts poorly with the corrosion byproducts, a float bowl that traps the worst of the water-ethanol layer right where the pilot jet pulls from.
The fix is the petcock, not the bottle
Run the float bowls dry before the bike sits more than two weeks. Turn the petcock off, let the bike idle until it stalls. Five seconds at idle, no extra effort. The bowls are empty, there is no fuel left to varnish, and you have not introduced any air into the system that wasn’t there already.
This single habit eliminates ninety percent of the spring-start phone calls we get. You do not need a new fuel system. You do not need to chase E0 across three counties. You do not need a bottle of anything. You need the petcock off and an empty bowl.
You do not need a new fuel system. You do not need to chase E0 across three counties. You need the petcock off and an empty bowl.
Why we don’t recommend stabilizers
Sta-Bil red, Sta-Bil 360 Marine, Star Tron, the hardware-store house brand. We’ve watched this argument cycle through every Triumph forum for fifteen years, and we’ve seen the same varnished pilot jet behind every label.
The marketing claim is real for fuel that sits in a sealed drum. A vintage motorcycle carb is not a sealed drum. The bottle preserves the fuel still in the tank, more or less, for a few extra months. It does not preserve the fuel sitting in the float bowl right next to the brass jets. That fuel evaporates, leaves varnish behind, and the varnish is what plugs the pilot circuit when you go to start the bike in March.
Stabilizer in a tank full of fuel that sits is still a tank full of fuel that sits. The bowls are the part that costs you the spring weekend. Empty the bowls and the stabilizer question goes away.
Short sit, long sit
For anything under a month, run the bowls dry and leave the tank as full as it happens to be. That is the whole protocol. For four months or more (winter storage in a humid garage): drain the float bowls at the drain screw to be sure they are actually empty. Top the tank to keep condensation down. Pull the petcock line off the tank if you are paranoid. Put the carbs in a sealed bag with a small desiccant pack if the garage gets damp.
Ethanol-free gas in California
Harder than it used to be. CARB rules pushed E0 out of most station forecourts. Pure-Gas.org maintains the closest thing to a working map, but the data goes stale. Call ahead.
A few are still selling E0 in Southern California. A handful of small marinas (Marina del Rey, Long Beach). Some race shops sell drums of 91 unleaded race gas to walk-in customers. A few aviation FBOs will sell 100LL avgas, which is leaded and will foul a modern plug but works on an old Triumph in a pinch.
Most of our customers do not chase E0. They run E10, run the bowls dry, and never call us in March. That works.
The seals and parts worth upgrading
If the carbs are coming apart anyway: Viton-tipped needle valves replace the original rubber-tipped versions and survive ethanol. Buna-N O-rings hold up where the original cork and pressed-paper gaskets do not. Most Amal rebuild kits sold today already use these materials. Confirm before you buy.
On the tank side: an original Triumph steel tank with a tan sealant inside (used by previous owners through the 80s) will not survive ethanol. The sealant bubbles, peels, ends up in your carbs as orange flakes. Caswell or Kreem (the modern formulations) are ethanol-safe. If your tank has flaky old sealant, it has to come out before you do anything else.