1955 evinrude 25hp backfires

[cbouch]

I have a really clean 25hp evinrude electric start that has not been run in a number of years and now need to get it going. Compression test approx 110-115 in each cylinder. Spark on lower cylinder real weak if any on upper great spark so for fun tried to start and engine backfired a couple of times. Pulled the flywheel and cleaned the points..coils looked like they were replaced..put it back together and had same problem..need to clean carb and replace coils, points, wires and condenser along with impeller...anyone have any input on what causes backfiring?? Thanks

 

[jimmbo]

Plug wires swapped, gap on points incorrect, broken/damaged reeds, carb too lean are some causes

 

[Chinewalker]

First guess would be plug wires swapped around. FRONT coil fires the TOP cylinder. Small coil wire to points runs to point set counter clockwise from the coil, tucked down and away from the cam.

 

[F_R]

Excessive cranking of a motor that will not start and run can result in much gas being pumped into the exhaust housing. Then a cylinder may fire, blowing flame into the gas-charged exhaust housing, resulting in a loud explosive backfire. Anybody old enough may remember how we used to do that with our car, revving it up, turn the key off, and back on, causing a loud backfire out the exhaust. Till we blew the side out of the muffler.

 

[boobie]

I've got some mufflers to my credit too F_R. LOL.:lol: