Yamaha TRX850 Enthusiasts Forum

On the standard carbs if you look from the right hand side of the bike at the rear of the carbs there is a hose that runs from immediately between them. On mine this hose routes down the right hand side of the engine (with the vacuum hoses from the opposite side of the carbs/front of the engine intake) and just ends unplugged about 6 inches from the fuel pump. Is this supposed to be attached to anything? Mine looks like it has fuel residue at the end.

The reason I was looking at this is that the bike died tonight. It started spitting and backfiring all of a sudden, ran out of power and died. Luckily I could pull in under a light (torch now added to the tool kit) and found that one of the vacuum hoses had become detached. I couldn't find where it re-attached in the semi-dark. I got the bike restarted but it was running rough at about 900rpm. Blocking the vacuum hose brought the idle back up and it ran normal. I had a pen on me that blocked the hose nicely so thought this would get me home. This got me going for a few minutes until the float bowl emptied as I guess no fuel was flowing into the carbs. Switching the fuel cock to prime got me home. 10 minutes with a torch found the vacuum nipple. The bike seems to run fine now but I'm keen to know what the mystery hose is. Is it some sort of drain?

Is it one of the vacuum take-off hoses? (On mine) the left one connects to the fuel tap and opens it to allow fuel through as the engine is running, the right one connects to the fuel pump. If the bike ran ok on 'prime' with the hose blocked it sounds like the hose that usually fits on the fuel pump came undone and it was drawing air in through the open hose until you blocked it off.

It would be easier with a picture but the ones I took are just a dark mess.

Yes the hose I plugged was a vacuum hose from the r/h side cylinder. However the mystery hose is not one of the two vacuum hoses from the front of the carbs/engine intake. The mystery hose is on the back side of the carbs and doesn't connect to one carb - it connects in the middle of the two carbs right in the centre. This is the one that is still unconnected to anything.

In the centre of the carbs there is only the fuel intake & fuel overflow, unless I'm mistaken...

Sound like a vacuum issue you describe though, one goes to the fuel tap & the other to the fuel pump, if either of those aren't connected you will run into trouble.

See if it will run with the fuel tap set to prime.

Rubes I recently solved the same problem on my bike, if you want I can have a look? Should take a minute.