I have a 56 Yamaha ybr 125 not a custom, The bike runs fine until all of a sudden it dies, it feels as though fuel is being starved as when it happens it feels as though the back brake is being tapped a few times then it conks out and if I twist the throttle nothing happens, power is still on though ie indicators and neutral light. It then will not start what so ever until I worked out that if I removed the fuel cap it fires up again. I believe it could be pressure in the tank, I have am hoping to look at it myself before forking out monies to a garage.

I have put a new battery on since this has happened, also cleaned the air filter and emptied the crankcase breather.

Any help would be great!

Hi,

Is there any noise (hissing) when you remove the tank?

If a vacuum is created by having no vent in the cap,then the fuel won't flow.

To be honest. I have only had this on cars where you have a fuel pump sucking fuel from the tank, the tank vent gets blocked,or someone has put on an non vented after market filler cap.

If you have some idea how far you can travel before cutting out, pick somewhere safe, I would then suggest taking the fuel pipe off the fuel tap before undoing the cap,if you have no fuel,release the cap,and see if any comes out. Then it would suggest the cap is faulty.

Be ready to turn off the fuel tap if it does start to flow.

If fuel comes out before releasing the cap,then it would at least take non venting out of your thoughts.

Good luck

Pete