1991 vmax.running very rough needed the choke on to keep running below 2000 revs.exhausts to both r/hand cylinders very hot, both l/hand cylinders only warm.carbs were stripped down and cleaned with carb cleaner and compressed air.reassembled as yamahas tech manual advises.no wear or defective parts found. tried to start engine,same problem.checked fuel to all carbs,have good spark on all plugs,tested coils all readings were good.still wouldnt start.sprayed fuel into carbs with airbox off,engine fired up but will only run on choke and at very high revs.cannot run engine enough to set anything up if needed.spitting back through carbs.stripped and cleaned carbs again,still no change.meantime whilst trying to sort this the starter clutch gave up,£128.any advice greatly appreciated.

vics, January 2011

noibbo i looked at the slides and they are the right way around so its not that ,but thanks for the suggestion anyway.

vics, January 2011

carb slides incorrectly fitted

noibbo, January 2011

ok good luck with that and please let me know how it goes vic.The last vmax i worked on was one i put v boost on it made a good improvement in power.

adam bike doctor(of milton keynes motorcycle centre), January 2011

thanks doc will take your advice and have another go at the weekend.

vics, January 2011

it sounds like there are internal parts of the carbs blocked up especially on the pilot circuits,i would clean these with an ultrasonic cleaner if i were you the spitting back problem is due to weak running,and having to have the choke on is because the pilot circuit isnt providing enough fuel.i cant remeber off the top of my head if the bottom of the fuel tank is higher than the carbs?if it isnt then there must be a fuel pump on it either an electric one or a pneumatic one.This would of course be a good reason for feul starvation if the pump isnt working .have you tried running the bike with a container hanging above the bike with fresh fuel in it ?and i take it the fuel in the tank is fresh too as the shelf life of petrol these days is very short.and are all the carb balancing adapter holes blanked off as they will be sucking air into them as would any leaks on the inlet manifolds rubbers or orings that go between the head and the inlet manifold rubbers.

adam bike doctor(of milton keynes motorcycle centre), January 2011