Street Twin/Cup Tank drain | GTAMotorcycle.com

Street Twin/Cup Tank drain

nikos1965

Well-known member
Does anyone know how to drain a gas tank on a Triumph Bonneville Street Cup? Theres is nothing on youtube on this. Somebody mentioned siphoning would be the only way if thats true but what about the fuel lines than?
 
It's probably fuel injected which means siphoning the tank, it probably wont gravity drain as the internal fuel pump will stop the fuel flow. If your buddy had premium fuel in the tank, it might run on that -- i'd try that first. If it won't start, siphon off the existing fuel then refill with a few litres of 94 octane non ethanol premium. It might crank for a bit, but Ill bet it fires right up.
 
It's probably fuel injected which means siphoning the tank, it probably wont gravity drain as the internal fuel pump will stop the fuel flow. If your buddy had premium fuel in the tank, it might run on that -- i'd try that first. If it won't start, siphon off the existing fuel then refill with a few litres of 94 octane non ethanol premium. It might crank for a bit, but Ill bet it fires right up.
I just wanted all the old gas out since this bike has been sitting for 3 years. Would siphoning be sufficient in this situation?
 
I just wanted all the old gas out since this bike has been sitting for 3 years. Would siphoning be sufficient in this situation?
Siphon and refill with non-ethanol hi test as mm said (although I dont know if you can get 94 ethanol free, 91 ethanol free would be fine).
 
I just wanted all the old gas out since this bike has been sitting for 3 years. Would siphoning be sufficient in this situation?
The problem with old gas is mostly if it's an ethanol blend. 3 years is long, but it's not the worst I've seen. I've started old motors on 10 year old gas, they don't run too well but that's often fixed with new gas.

If there are some other issues. Ethanol is hydroscopic, meaning it will pull moisture from the surrounding air. That's generally not a huge problem for a motorcycle because the tank is so small so the amount of ethanol in the fuel will also be quite small. Probably the biggest problem small engines face is corrosion. Water dissolved in gas can react with the metals and plastics in a fuel system, this problem gets bigger as the motor gets smaller. On a Bonnie sitting 3 years with 1K on the clock -- id slap $10 on the table saying it will fire right up with a good battery and the existing fuel. 2 weeks ago I started a 45 year old car that sat with unknown gas since 2015 -- it fired, ran rough but after adding 5 gallons of fresh gas things cleared up and it ran like a charm.

For piece of mind, siphon it out (or ride it out).
 
The problem with old gas is mostly if it's an ethanol blend. 3 years is long, but it's not the worst I've seen. I've started old motors on 10 year old gas, they don't run too well but that's often fixed with new gas.

If there are some other issues. Ethanol is hydroscopic, meaning it will pull moisture from the surrounding air. That's generally not a huge problem for a motorcycle because the tank is so small so the amount of ethanol in the fuel will also be quite small. Probably the biggest problem small engines face is corrosion. Water dissolved in gas can react with the metals and plastics in a fuel system, this problem gets bigger as the motor gets smaller. On a Bonnie sitting 3 years with 1K on the clock -- id slap $10 on the table saying it will fire right up with a good battery and the existing fuel. 2 weeks ago I started a 45 year old car that sat with unknown gas since 2015 -- it fired, ran rough but after adding 5 gallons of fresh gas things cleared up and it ran like a charm.

For piece of mind, siphon it out (or ride it out).
thanks I will be syphoning it out. Do you think I should be flushing the brakes and the cooling system since its been sitting for so long? Somebody mentioned that. I just want to get it running. Will be towing it home on Monday to get the cake of grease and dust off it and begin the rest.
 
Don't take this the wrong way - it's one thing to buy a bike to learn how to wrench on it when you are also the rider. But if you plan on selling it soon, and you are not 100% certain of what you are doing, it might be better to not mess with it more than you have to. I would leave the brakes and cooling system alone, if they appear to function normally after you have started the bike.
 
thanks I will be syphoning it out. Do you think I should be flushing the brakes and the cooling system since its been sitting for so long? Somebody mentioned that. I just want to get it running. Will be towing it home on Monday to get the cake of grease and dust off it and begin the rest.
No. Not necessary based on mileage and time.
 
thanks I will be syphoning it out. Do you think I should be flushing the brakes and the cooling system since its been sitting for so long? Somebody mentioned that. I just want to get it running. Will be towing it home on Monday to get the cake of grease and dust off it and begin the rest.
The brake fluid and the coolant should be changed every two years.

However; if you just want to get the bike running, I would just let the buyer know that it hasn't been done yet. When I buy a used bike, I'll do the oil, coolant and brake fluid regardless just for the peace of mind.
 

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