25 HP mariner backfires but doesn't start

[Buckeyedude]

To get everyone up to speed: this is a 1988 motor, hasn't been used in around 10 years. Kept inside, cylinders sprayed and turned over several times a year. It had a new power pack or something put on it way back when I pulled it off my boat.
Currently, I have installed a new impeller and lower unit oil. New plugs, fresh gas, new line and bulb.
Have good spark, motor turns over but backfires out the exhaust. I've done some reading and think it might be something wired wrong on that power pack because the plug wires aren't long enough to mix them up! Any ideas or a wiring diagram out there?

 

[flyingscott]

Did the motor run correctly before you replaced the powerpak and if not. Did you reverse the wires from the powerpak to the coils that will do it. should be 2 green wires one has a white stripe and yellow stripe I believe and they need to go to a certain coil. Or try switching the spark plug wires around on the coils. Or it could be a flywheel key is sheared.

 

[Buckeyedude]

Yes, it ran fine , well until it needed the new pack!
I never used it after that, because of a lack of time and eventually getting a 9.9 to put on the boat to run around the local 10 HP lakes.
From what I've read, that makes sense about the wires being switched. I will check it out after work tomorrow and keep you updated. Thank you for your reply!

 

[Buckeyedude]

Switched wires on coils started on the first try! Thank you!