Backfire rebuilt Johnson 115 HP '83

[boboat]

I have fuly rebuilt mine V4 115 hp ''83 (started in 2000)
Put in oversized pistons new bearings seals and so on (a hell of a job)
Now it runs but gives a big spontanios backfire from exhaust in idle and half gas

-There are now plugwires crossed
-New coils and secondhand cdi unit's
-looked at flywheel key looks fine to me

Still the backfire

could this be the carbarateur?????
Or the ignition timing ??? have not set full advaced timing???

Need help from the experts Anyone idea's
I would like to go out boating with this baby here in the netherlands

 

[Joe Reeves]

Re: Backfire rebuilt Johnson 115 HP '83

The outside flat portion of the flywheel key must be perfectly vertical, that is straight up and down with the engine, not aligned with the crankshaft taper.

The key must be the factory key part number 307480, not some run of the mill key out of a hardware store, and it must not have any worn edges that might throw it ever so slightly out of time.

The flywheel nut must be torqued to exactly 105 foot pounds.

The primary wires from the powerpacks to the coils..... the orange/blue wires lead to the top coils. Check them.

Strange..... usually anything out of the ordinary that would actually cause a backfire would result in a constant ever repeating backfire.

 

[boboat]

Re: Backfire rebuilt Johnson 115 HP '83

thanks joe reeves!!!!

I will put in an new flywheel key.
and will check wires

Just put a new flywheel from an ?78 on it wiil run it today

will send my report after i have run it with new key.

 

[boboat]

Re: Backfire rebuilt Johnson 115 HP '83

thanks joe reeves!!!!

I will put in an new flywheel key.
and will check wires

Just put a new flywheel from an ?78 on it wiil run it today.

will send my report after i have run it with new key.