1978 85HP Evinrude Backfires

[bcomer]

My 85HP Evinrude sometimes backfires --almost violently when starting. What would cause this? What to do to recify?<br /><br />Also, not sure exactly how reed valves work but I know a bad valve in a car can cause backfire. Do reed valve need to be replace periodically? How do I know if they are operating correctly? Are they hard to change?

 

[rodbolt]

Re: 1978 85HP Evinrude Backfires

hello<br /> check the pickup timing. check that the choke butterflies are closeing properly. dont sweat the reeds. if a reed breaks then it is always broke and you will notice it idles nasty and wont make power. the backfire on a two stroke can only be caused by two things. 1 is a misfire of the spark at a point where the piston is below the ports in the cyl. not likely but does happen on occasin. 2 a lean condition due to starting procedure or fuel delivery or a poor linkage sychronization, more likely. all the reed is is a thin strip of metal (stock) that only flexs one way to allow fuel/air to be drawn in and then compressed by the downward motion of the piston.(primary compression).chgeck all the subsystems as per your service manual for proper operation and you will find your problem.<br /> good luck and keep posting

 

[Joe Reeves]

Re: 1978 85HP Evinrude Backfires

In addition to Rodbolt's post, I'd *** that if you've had the flywheel off recently, perhaps you didn't torque it properly.<br /><br />The flywheel nut on that modle must be torqued to exactly 105 foot pounds, otherwise the flywheel key will shear, throwing the engine out of time.<br /><br />Normally this shearing problem will not allow the engine to start at all, and will cause the engine to fire out the exhaust, but there are exceptions.<br /><br />Something to check into perhaps.