750 Commando fibreglass tank

Any fibre glass tanks that are 40 years old are likely to be coming to the end of their lives, I've got one on my Montesa (74) and if I leave petrol in it for any time it goes sticky inside.

I think if it were mine I'd clean it out with acetone and line it with a modern ethanol proof liner designed for glass fibre tanks. I'd still drain it if I left it for any time.

Mine only gets wet on race days!

Paul,

before you use any sealer fill the tank with Spax screws and

shake it like a Polaroid picture!

The sealer will stick better to the rougher inside.

A seller of tank sealers gave me that advice.

Use high octane gas with lesser ethanol.

On my 70 Roadster, now converted to a "S" Type

was also fitted a plastic tank. It was painted black but

underneath was the Fireflake Royalblue on the tank and side covers as a gel coat.

According to the records it was delivered to Gus Kuhn in May 70 as a black roadster which later found its way to Germany.

But you better look for an steel tank.

Depends where you live Paul, but my best advice is to use E0 petrol and avoid EN228 (5% Ethanol)

Esso Supreme Synergy 97 RON is guaranteed E0, outside of Devon and Cornwall, Teesside and Scotland.

Good idea to clean and line your tank, but be careful what sealant you use, some don't work in GRP . fibreglass.

Fibreglass tanks are legal on old bikes. There have been new ones available until quite recently. Caswells sealer seems to get good reviews but not sure if it's still available. I would be tempted to use the bike and see what happens, it's not going to turn to jelly before your very eyes. If it has had any repairs after damage, then petrol will seep into the fibreglass and eventually make an appearance under the paint. If there are any sign of repairs then I would line the tank before using it. I lined a tank many years ago with fibreglass resin and hardener. I suffered for months with sticking float needles as the resin came through the taps. Use a proper sealant. Steel tanks are now available and are getting better, but they are not quite the right shape to the trained eye

If that tank is going to be used without ethanol proof sealant then E 0 petrol has to be used. Otherwise you are just asking for trouble. Sticking float needles and gummed up carbs are the best you can hope for while the worst is fuel landing on a hot engine.

Ethanol is a safety hazard but too big to fail!