1972 Johnson 50hp. wont start pops white smoke out of carbs and out of exhaust.

[bagnallt]

HI ...
Well here goes..... I have a 50hp Johnson 1972 with electric shift. I have had it a couple of months. It seemed to be ok but developed an iding problem. I rebuilt the carbs cleaned them reset the idle screws and it was ok. Yesterday I was flushing the motor checking ready to go out and it slowly died. No nasty noises no over heating it was pumping water great!!
So .. I tried to start it and it cranks freely but wont start. All it does is turn over then a loud POP and white smoke comes out of the exhaust and out of the carbs...
I would appreciate any help ... I have a feeling it may be the reeds but before i try to replace them would like some guidedance .. ALso could it be a bad fuel pump??
BTW... It has good compression both cylinders, good spark too.. stong and blue. gas is fresh.... all lines cleaned.

 

[Texasmark]

Re: 1972 Johnson 50hp. wont start pops white smoke out of carbs and out of exhaust.

Could be fouling plugs or might need a decarb job.....see archives. White smoke to me is combustion that halfast happened. You only partially blew up the contents of the cylinder. I'd assume you are running the 50:1 premix fuel. I don't see the fuel pump being the problem cause you are apparently getting fuel, but a bulb squeezing till firm would bypass any doubts about the pump for a short bit of running, or if you just stood there and kept squeezing the bulb while it's running.

Any reason why your timing would have changed? Hit any stumps or anything like that your last time out? All the control linkage in the engine lubed up?

Best I can do from here.

Mark

 

[tashasdaddy]

Re: 1972 Johnson 50hp. wont start pops white smoke out of carbs and out of exhaust.

possibly a sheared flywheel key. you have to remove the flywheel, and use a new OEM key, hardware store ones will not work. you need a puller to pull the flywheel, #8 harden bolts, as standard will strip off.

 

[bagnallt]

Re: 1972 Johnson 50hp. wont start pops white smoke out of carbs and out of exhaust.

Hi mark...
It was running ok last time we were out.
I changed the plugs and still the same.
Primer bulb gets hard. Still same thing.. I can crank it but it wont start just POP followed by one puff white smoke out of carbs and exhaust hub.
Thanks for your help.

 

[HighTrim]

Re: 1972 Johnson 50hp. wont start pops white smoke out of carbs and out of exhaust.

Firing (backfiring) out the exhaust port can be caused only by having the ignition system fire a particular cylinder when the exhaust port is open (piston down). This would sound like a shotgun going off..... is this the condition that you're experiencing?

This can be caused by a sheared flywheel key, or a flywheel with melted (moved) center sensor magnets if they exist, or having the timer base leads routed incorrectly to the powerpack, or having the leads from the powerpack to the coils reversed to mention a few.

 

[bagnallt]

Re: 1972 Johnson 50hp. wont start pops white smoke out of carbs and out of exhaust.

hi Mark... the noise is a loud pop not like a shot gun... like pop pop asfter a few turns of the engine....

 

[Texasmark]

Re: 1972 Johnson 50hp. wont start pops white smoke out of carbs and out of exhaust.

This just didn't happen. Go over what this rig has been exposed to since your last trip when it was running ok. And this new gas you got, where'd you get it? How do you know it's good? Where'd you get the oil? Is it the correct oil mix?

Your flywheel key shouldn't be all of a sudden sheared unless you hit something the last time you used the engine, but your spark advance could be gummed up and since it is winter time, the grease could be gummy and delay your spark enough to fire at the wrong time possibly.

Or a rat could have gotten in there and gnawed up some wiring.

Or your high voltage leads could be crossed and you are firing the adjacent cylinder when you aren't supposed to because the insulation broke down.

Mark

 

[Texasmark]

Re: 1972 Johnson 50hp. wont start pops white smoke out of carbs and out of exhaust.

"Electric Shift"......do you know that the lower unit is in N when you think it is. I think this engine had a F gear fail safe. If you lost power to the lower unit you could still get home. If trying to start in F you could be loading the engine and experience what you are talking about.

Mark

 

[bagnallt]

Re: 1972 Johnson 50hp. wont start pops white smoke out of carbs and out of exhaust.

whoop hi chris ... the engine makes a pop not a like shot gun firing Its a loud pop. not like a backfire i hear from a car.

 

[bagnallt]

Re: 1972 Johnson 50hp. wont start pops white smoke out of carbs and out of exhaust.

Hi mark.
The motor is definately in N. It will not crank if its in F.
We didnt not hit anything last time out. But when i think about it a few weeks earlier we hit a submerged stum. ( Lake Rouseau Fl) We have been out twice since then so i guess it might have weakened the key?
The only other thing was that a few days earlier it wouldnt start and i found the primer bulb was shot. I replaced it and checked the idle settings on the carb and it fired up. But like a said yesterday i fried it up it idled for a few minutes and slowed sputtered and died. Then it wouldnt start just this turning over and then POP...... white smoke from carbs and exhaust.
Thanks ...

 

[bagnallt]

Re: 1972 Johnson 50hp. wont start pops white smoke out of carbs and out of exhaust.

ALso ... Gas is fresh 50:1 mix. In a clean fuel tank. Got new gas so that when i cleaned the carbs I knew that wouldn be the problem.

 

[bagnallt]

Re: 1972 Johnson 50hp. wont start pops white smoke out of carbs and out of exhaust.

hi all again...
I check all the wires ... non chewed. I check the neutral start... its in neutral. It wont even atempt to crank in F.
One question. to add ..
I can turn the flywheel by hand quite easily... I do feel resistance when the pistons move down in the cylinder if you understand what I mean....
I did find that the large nut on top of the fly wheel is loose. IT was basically finger tight against the flywheel not tight against it..

 

[bagnallt]

Re: 1972 Johnson 50hp. wont start pops white smoke out of carbs and out of exhaust.

I forgot to add the question..
Ok.. I was emailed by a guy called boatcap. he said that it could have a shot piston or lifter.
Wouldnt i hear a grating, grinding or knocking noise when it cranks indicative of an internal engine problem.??

 

[tashasdaddy]

Re: 1972 Johnson 50hp. wont start pops white smoke out of carbs and out of exhaust.

you found your problem, the loose nut one the flywheel has allowed the flywheel to shear the key, when this happens it throws every thing out of time. you need to pull the flywheel, and replace the key OEM part# 307480. bet it runs like new. then torque the flywheel nut to 70 -85 ftlbs.

 

[bagnallt]

Re: 1972 Johnson 50hp. wont start pops white smoke out of carbs and out of exhaust.

hi again...
One final question, as dumb as this sounds, when i replace the flywheel key and fly wheel. will the engine need to have the timing checked? And any one got a ball park figure of the cost?? and even the cost of someone replaying the key for me? Thanks

 

[tashasdaddy]

Re: 1972 Johnson 50hp. wont start pops white smoke out of carbs and out of exhaust.

pulling the flywheel is a simple job, the key is $4.00. the motor should start right up, just like before. i did mine in 30 minutes. shop should do it for $100.00. i have a 71 50hp.

 

[HighTrim]

Re: 1972 Johnson 50hp. wont start pops white smoke out of carbs and out of exhaust.

Agree with tash, get a manual,puller and a torque wrench and do it yourself. Just ensure that you do in fact torque it, or you will experience the same problems down the road.

 

[Harker]

Re: 1972 Johnson 50hp. wont start pops white smoke out of carbs and out of exhaust.

One more thing, 2 strokes don't have lifters. Take the nut off and look at where the slot in the flywheel lines up on the shaft. The shaft will have a slot too for the key and they should be lined up. If the slots are off it is a sheared key. If you don't have a torque wrench and gear puller with the correct hardened bolts...and a shop manual...and don't feel comfy working on it, take it to a mechanic you trust and have them do it for you. You DID put the plugwires back on the right cylinders?

 

[wavrider]

Re: 1972 Johnson 50hp. wont start pops white smoke out of carbs and out of exhaust.

Pulling the flywheel is not a hard task. If you do not have a flywheel puller you can go to your local auto parts store, the one where they say get into the zone, autozone. They have a loaner tool program where you put a deposit on the tool and when you bring the tool back you get your deposit back, just another way to get customers in the store but it will save you the cost of a puller.
You do need the #8 bolts, the standard wil strip, don't have to ask how I know, I just know you need #8 or it will make more trouble.
As far as replacing the key, there is a slot in the crank shaft and another one in the flywheel, line them up when you install the flywheel, torque them down to specifications and start your engine.

 

[bagnallt]

Re: 1972 Johnson 50hp. wont start pops white smoke out of carbs and out of exhaust.

Hi all... well I got the key, a puller and a torque wrench. With the help of my wonderful wife we set about removing the flywheel. With my wife holding a wrench to stop the flywheel moving it came off very very easily with the puller infact it came off too easily. The key was completely sheared in two, one half in the shaft and the other in the fly wheel. It was also very ver soft.. like aluminum. I could not get the new key to fit.. but my wonderful wife ( she taught me how to fish in the US yep I am a brit.) fitted it with ease. The flywheel slid right back on and i torqued it as per suggestions here. Fired her up and WOWOWO ... The motor sounds great.!!
A big thanks to everyone who helped. And I mean A BIG THANK YOU!