Bike sputters and loses tach

[soovmaxguy]

I have a 1985 Yamaha Vmax with Dale Walker exhaust.Got it from a good friend that was on here lots.He got the jetting all figured out from you guys on here and wanted me too have the bike. (he is no longer with us).This is my 4th Vmax.I need some help.When the bike is cold it runs fine,but as soon as the bike gets warm it spits and sputters and wont rev past 6000 and then the tach drops too zero.It sounds like its on 2 cylinders.I tried by-passing the kick stand safety switch but got no better.The rectifier gets really hot and was wondering if that was the problem, I need some Vmax guru help.It started with a stumble at 6000 rpm the other day and has got too the point where the bike is unrideable now.Thank for any help

 

[MaxMidnight]

If it is going on to two cylinder then it is likely that one of the pick-up coils is duff when some heat gets into it.

As you loos the tacho as well it will be the one that feeds the grey tacho wire.

 

[bumper]

mine did the same. sputtered and lost the tach and then quit. It was the cdi box.

 

[PaulVmax]

+1 to what max said look for brakes in the wires after all the bike is 28 years old

 

[soovmaxguy]

I will check the coils and find the grey wire.It sure does seem like its on 2 cylinders and will come back too 4 at any given time.It started doing this at 6000 rpm and i was thinking he never got it jetted right till it got worse.Now as soon as its hot it sputters bad and the tach quits working. Will keep you posted

 

[soovmaxguy]

When you say pick-up coils,you mean with stator or coils on top of battery?

 

[MaxMidnight]

When you say pick-up coils,you mean with stator or coils on top of battery?

Pick-up coils next the stator - one p/u coil controls the signal to two ignition coils.

If it seems intermittent then, as Paul suggests, look for a poor connection.