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Johnson 2trk 50hp 1971, no combustion

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Fe1ke

New member
Hey guys,

Im new here but Im looking for some much needed help.
I recently picked up a Johnson 2trk 50hp 1971 outboard and it wont start. my knowledge is not super crazy, and some terminolgy may be slightly inccorect.
Iv checked spark plugs which both work well, theres seems to be presure in the combustion chamber (i dotn have a preaure meter thing to put inthe spark plug fitting) however when turning the motor slowly there is presure build up.
I have fully cleaned the carbs (not changed fuel lines) and the motor still doesnt start. There is fuel coming through the carbs also.
I have also tried start the engine by just spraying fuel directly without the crbs on to see anything. Once in a while htere will be a nice big pop but no real luck.
What im thinking is that the gasckets between the carbs and the engine block are too old and are letting too much air in while starting, and not only that the gascket of the airbox has a small gap which allows more false air in.

there is a new battery hooked up, and everything else seems to be in working condition.

What do you guys think?

(please dont respond if your responce is: get a new outboard :)

Fe1ke

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Fe1ke, you seem to be focusing on not getting enough gas. I suggest it is getting too much gas. The loud explosion was excess fuel igniting in the exhaust system. Related to too much gas is no spark or spark at the wrong time.
 
fdrgator said:
Fe1ke, you seem to be focusing on not getting enough gas. I suggest it is getting too much gas. The loud explosion was excess fuel igniting in the exhaust system. Related to too much gas is no spark or spark at the wrong time.
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Thanks, the ignition coils are in pretty bad shape (never replaced) and they are a bit corrodid (not crazy). but there is still ignition. Would that cause that much of a problem that there is no cumbtion at all in the chamber?
 
Well that certainly is a clue. You really need to do some orderly troubleshooting. That begins with a compression test. "Feels good" means nothing. Follow that with a real spark test. It should produce a 7/16" gap open air spark with ease. if all that passes, check spark timing. Timing light required. Actually, timing is what racerone had in mind when he suggested checking the flywheel key. That costs nothing.
 
And you can not find a sheared key with a timing light.-----This should be easy / simple trouble shooting.----But sometimes owners make it difficult.
 
Thanks for the suggestions i bought the motor with a boat for an absolute bargain, so i assume the owners before me tried the simple cleaning of the carbs to fix the motor and that didnt work. The nut of the fly wheel is also slighty damaged becasue someone tried to get it off with impropper tools or whatever, so now im assuming they looked at the pickupcoil and tried to repair and thought it was a lost casue, as its an old motor and parts are not easierst to get. however I will keep trying. im goign to work on her this weekend hopefully she speaks. I just dont have all the tools so im trying to spend as little as possible on things I do not need to buy.

last question tho,

even with low comrpession, shouldnt the motor if ignition timing and fuel were nominal, at least give some form of life with some combustion in the chamber?

if yes, i think ill have too look at the pick up coil, the flywheel key, and new ignition coils.

Thanks already
 
racerone said:
And you can not find a sheared key with a timing light.-----This should be easy / simple trouble shooting.----But sometimes owners make it difficult.
Click to expand...

Um-m-m, you can't? Spark is produced as magnets pass the stator and timer base. Flywheel key establishes flywheel position to crankshaft. If flywheel is not on correct position to crankshaft, spark will not occur at right time in relation to piston TDC. True, it is not an accurate way of checking timing, but if it is so far off that it won't run you should get at least a clue. Am I wrong?
 
Post #7. Aha! Flywheel nut buggered up. You can bet he didn't properly install the flywheel nut with a torque wrench. All the more reason to suspect a sheared key.
 
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