comtech147

I have two 1974 Yamaha DT 360 enduros. Both will start and run clean for around 3 seconds and then die. The carbs have been cleaned the fuel and plugs are new. all lighting and kill switches have been disconnected. Both bikes do exactly the same thing. Has any one experienced this. I am not very good at wiring. I have an ohm meter but do not know how to use it. Can any one help? Bill