My 4rt came with a check valve installed in the fuel cap breather vent hose. The check valve allows air to escape from the fuel tank. I think this is upside down. Isn't the breather supposed to let air into the tank, or is there something special about the whole fuel injection set up?

Well Fuel Injection requires tanks to be pressurised, hence the Whoosh when you open your petrol cap on a car. This is why the tank is built of metal so it resists collapse.

Well Fuel Injection requires tanks to be pressurised, hence the Whoosh when you open your petrol cap on a car. This is why the tank is built of metal so it resists collapse.

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I think you'll find that if the petrol tank can't get air in through the breather your bike is going to stop pretty quickly. What fills the tank after you've used up all your gas? Air. The pressurisation of the system occurs between the fuel pump on the bottom of the tank & the injector.

ask sandifords thats what i did,

i would tell you but i cant remember.

Thanks, gentlemen. I see that the factory pictures of 4RTs do not show a check valve in the breather hose. Also, the parts book that I downloaded via this site (thanks very much!) doesn't list a valve, either. I'm going to turn the hose end for end so that air will go into the tank and gas can't spash out of the hose. If the engine works the same or better, I'll quit while I am ahead.

I have relocated my check valve on the breather hose about 2" from the top of the fuel cap. With this in mind the check valve should be installed with the white ring toward the fuel cap.

I bought my bike used, so I'm not sure if the check valve is a factory item. The 4rt pictures on the Montesa advertising do not show a valve. Mine is spliced into the middle of the breather hose. The valve does have a white ring, but I'll have to run home to see which direction it faces. Thanks.

Okay, I've got the white ring installed toward the fuel cap now. It was upside down before. Thanks.