Exuast backfires 1976 25hp evinrude

[nick271]

G'day guys I hit a large hidden log a couple weeks ago on the water it rattled the motor hard after which it chocked and splattered a lil before dieing
I couldn't get it to re start luckly someone came by and gave me a tow back to the boat ramp
Well at the boat ramp I checked and had spark had compression had fuel all the way upto the plugs
Thought I might of flooded it so pulled the drain plug on the carbie pulled the spark plugs gave it a few pumps to drain it tried again still wouldn't fire but we'll I was trying to start the motor it was blowing black smoke out the exhaust and every now and then would back fire out the exhaust like a shotgun going off
This lead me to belive the timing was shot so I pulled the flywheel off and the woodruff key on the crank shaft was still intact are there any other reasons it would be backfiring well trying to start

 

[Nordin]

Have you checked the cam ring?
The flywheel key orientate the cam ring, if the cam ring and flywheel not lining up right it can back fire and would not run.
Have to ask too, are the HT wires at right spark plug?

 

[Michawilden]

Not accidentally switched the spark plug wires while testing for spark?

 

[saltchuckmatt]

That does it almost Everytime.

"The simplistic explanation is usually the best one"

Occam's Razor

 

[nick271]

Iv got the plugs marked 1 and 2 so I know which goes top and bottom and if it was as simple as I put the plugs on the wrong way it would of started on the water well I was floating and hadn't messed around with anything yet
Iv tried all the basic im looking for that 1 stupid thing that could of snaped to cause a issue so far I haven't found it
Cam ring is a good idea I'll check that next for sure

 

[saltchuckmatt]

Okay...
Couple of things, and this is for the future, wires going to the coils (not the plug wires) have a basic color and one stripe each. Blue and green. Blue is represented by the top cylinder (sky) and green is represented by the bottom cylinder (grass). That also works for the trim and tilt.

2 things that could have gone wrong when you "whacked" the motor.

Key looks fine but isn't. Did you pull the flywheel and lap it with lapping compound plus replace the key? Very cheap to do.

If so pull the lower unit (gear case) and start it without it. Don't run it long or jimmy rig a water hose to the pick up tube.

It will sound very loud.

Report back and let us know.

It's beer time for me!

 

[racerone]

Are you sure wires are colored like that on a 25 HP 76 model ?

 

[nick271]

Okay...
Couple of things, and this is for the future, wires going to the coils (not the plug wires) have a basic color and one stripe each. Blue and green. Blue is represented by the top cylinder (sky) and green is represented by the bottom cylinder (grass). That also works for the trim and tilt.

2 things that could have gone wrong when you "whacked" the motor.

Key looks fine but isn't. Did you pull the flywheel and lap it with lapping compound plus replace the key? Very cheap to do.

If so pull the lower unit (gear case) and start it without it. Don't run it long or jimmy rig a water hose to the pick up tube.

It will sound very loud.

Report back and let us know.

It's beer time for me!

1st

 

[nick271]

Okay...
Couple of things, and this is for the future, wires going to the coils (not the plug wires) have a basic color and one stripe each. Blue and green. Blue is represented by the top cylinder (sky) and green is represented by the bottom cylinder (grass). That also works for the trim and tilt.

2 things that could have gone wrong when you "whacked" the motor.

Key looks fine but isn't. Did you pull the flywheel and lap it with lapping compound plus replace the key? Very cheap to do.

If so pull the lower unit (gear case) and start it without it. Don't run it long or jimmy rig a water hose to the pick up tube.

It will sound very loud.

Report back and let us know.

It's beer time for me!

Love the tip about the blue and green wires very helpfull

 

[nick271]

Ok so problem has been fixed I originally had alot of trouble getting the flywheel off as it was stuck down harder than any fly wheel iv tried to pull not sure if the last person put it on to tight or if when I hit the log it Jared as it's been a decent motor for the 6 months iv had it but put the flywheel back on and low and behold she started up just like it used to
That being said I have done the dirty on the old girl as the flywheel strap wasn't strong enough so Rachel straped it down to get the bolt off
Now I'm not sure if it was the log that cracked it or me straping it down to apply extra pressure to crack the nut but iv snapped the exuast clean break
I'll start a new thread for some questions about that

 

[saltchuckmatt]

Well problem solved and problem added. We've all been there. Can't wait to help or try to help with the new problem.

As to Racerone's crafty little question?

I should have added....."lots of outboards" to the......message.

Pardon Monsieur!

 

[nick271]

Well problem solved and problem added. We've all been there. Can't wait to help or try to help with the new problem.

As to Racerone's crafty little question?

I should have added....."lots of outboards" to the......message.

Pardon Monsieur!

I did check and there is a blur wire and a green wire on both the 76 and the 78 even tho they are 2 difrent ignition systems

 

[saltchuckmatt]

I did check and there is a blur wire and a green wire on both the 76 and the 78 even tho they are 2 difrent ignition systems

Yeah, well he got me again!

 

[cyclops222]

I used up 3 flywheel keeys until I was told to torque the nut to 90 pound feet !!! Mechanic said back firing is normal if the Woodruff flywheel gets loose. A sudden prop stop can overload the KEY shape a little bit. Take apart flywheel & then put the key back in In a REVERSED STRETCHED position ? Now the ...RETARTED TIMING becomes a ADVANCED TIMING and runs O K. BUUTT If the stretched and reversed key is really ...TOO FAR ADVANCED ? You will ruin the engine over time.
Buy a brand new key & borrow a correct sized torque wrench to get the nut tight enough. Simple piece of cake.
Do not tighten that nut to correct pound feet ? Engine stop completely in middle of nowhere.

 

[racerone]

The flywheel taper and crankshaft tapers must be lapped together for a precise fit.---Use valve grinding compound.------The key locates the flywheel for correct timing.----The flywheel is driven by the locking tapers.----And 50 ft-lbs is correct for the flywheel on a 76 model 25 HP.----Tapers must be matched and assembled dry and clean.

 

[nick271]

The flywheel taper and crankshaft tapers must be lapped together for a precise fit.---Use valve grinding compound.------The key locates the flywheel for correct timing.----The flywheel is driven by the locking tapers.----And 50 ft-lbs is correct for the flywheel on a 76 model 25 HP.----Tapers must be matched and assembled dry and clean.

Do you have a vidio reference for this even if it's not for my motor even a Wright up about it to read just for more of an idea iv never heard of tapers or valve grinding compound but it sounds like something I should learn more about

 

[racerone]

It is a simple procedure.-----Perhaps you can find a video on U-tube.-----Explaining this to you.

 

[nick271]

For anyone else reading this thread trying to figure out what's wrong with your out board backfiring once you pull your fly wheel even if your key isn't snapped just bit the $8 bullet and replace it as small amounts grinding off it can do alot
As for lapping your flywheel this vidio isn't for a outboard but gives a great explanation on how and why to do it