Yamaha TRX850 Enthusiasts Forum

Dead stock TRX was running fine until yesterday now appears to be running very rich on left cylinder. Went through the hassle of replacing plugs, has fresh airfilter and all vac hoses appear fine and not kinked. The line from the LH intake to fuel tank base has fuel in it when disconnected, this has never been the case before. I am assuming this means almost raw fuel must be entering the head. 31000 trouble free kms to this point. Any ideas appreciated as she is my transport.

Sounds a bit lumpy at idle but symptoms far more pronounced in 3200-4000 RPM range.

If I cant sort it soon shes off to the Yamaha Doctors.

Split carb diaphragm?

Could be split fuel tap diaphram. Clamp off hose going to tap ( the one with fuel in it ) turn tap to prime. If it runs ok fuel tap is your problem.

Spot on Dobbo. Just got back from test ride when I saw your reply. Split in fuel pump diaphragm allowing fuel into vac line and straight into intake. Have "doctored" it to work normally but will be up for a replacement ASAP.

Remember to keep the tank fairly full during your doctoring. If the level drops below the carbs it won't gravity feed on "prime" (which is why it has a fuel pump in the first place).

Managed a temporary repair to the diaphragm itself so pump works as normal.