Flush out old fuel

Petrol lost its fizz? Here’s how to make a fresh start

Hiss and sniff

From the moment you fill your tank the fuel inside starts to degrade. Petro chemists describe petrol losing its ‘light ends’, the volatile components of fuel evaporating over time. The vapour you smell when you open the tank is essentially your petrol losing its octane. Stale petrol smells bit like varnish or paint, which indicates its ability to combust has diminished.

Peer inside

Petrol that’s been in your tank for a few months, say over winter, should be fine. But if you are going to recommission a bike that has been standing for a year or more then you should flush out the old petrol prior to restarting. Assess how much old fuel is in the tank by looking inside with a torch then find a petrol can big enough for it to be drained into.

Get some breathing space

Petrol vapour is flammable, even when degraded, so it’s best to either work outside or open all your doors inside your workspace. Make sure the bike is totally switched off and that there are no potential ignition sources in the area. Have workshop paper towel and a catch tray on hand to deal with any spillages while you are working.

Don’t be a sucker

If your bike is modern and does not have a fuel tap, you’ll need to drain the fuel out of the tank using a pump-action fuel siphon. Don’t be tempted to cut a length of garden hose and suck it out manually; a gob full of fuel is unpleasant and dangerous! Most motoring shops sell various types of siphons; this Draper one is ideal as it’s easy to use, good quality and value.

Plumb the depths

Find the tank’s lowest point – you may have to look under bodywork panels. When you’ve located the low point, insert the siphon pipe right down into it. If there is a direction arrow on the siphon check that it is pointing in the direction of the fuel container, as there will be a one-way valve that prevents air coming back up the pipe.

Start pumping

Pump the siphon until you see the petrol start to lift through the pipe. As soon as it descends lower than the tank, you can stop pumping and let gravity take over. You need to make sure the end of the pipe in the tank remains at the lowest point to ensure all of the fuel is removed – another pair of hands can be useful here.

Drain the pipe

When the siphon has emptied the tank, check with a torch to see that there is no fuel left inside; a small amount will not cause any issue when mixed with fresh. Remove the siphon from the tank end first and keep the pipe held high so any residual fuel left inside will drain out safely into the jerry can.

Fresh fossil juice…

If there’s still a significant amount of fuel left inside try relocating the end of the siphon in another corner of the tank to see if it will extract any more. Once it’s suitably empty, pour fresh petrol in via a filtered funnel. Remove any petrol cans and the siphon from the area of the bike. Check and clean up any splashes of fuel.

Don’t forget carbs…

If your bike is carburetted you should now drain the carbs, as there will be stale fuel left in the float bowls. Locate the drain screws at the bottom of each carb and undo them and wait for the fuel to run out into an empty container. Switch the tap to prime, or the on position, as this will fill the carbs up with fresh fuel prior to starting.

Check your other fluids

Prior to starting up, it’s good practice to check the fluid levels, too. If the bike is watercooled, inspect and top up the coolant level if necessary. And then check
the oil levels, both engine and gearbox. With everything OK, start the bike and warm it up slowly. Keep a visual check to make sure there are no leaks.