1971 50hp Johnson top dead on top cylinder

lil grox

Recruit
Joined
Jun 21, 2010
Messages
1
Hi, I recently purchased a boat with a 1971 Johnson 50hp on it. It had sat for 3-4 years before I took it over. The previous owner said it ran when parked. I emptied the old gas that looked like Coca-Cola out of the tank, replaced with fresh mixed fuel. Removed both carbs and cleaned them. Replaced needle and seats. Checked compression 150 top, 153 bottom. Spark tested and jumps nearly half an inch. New plugs gapped to .035. It started and ran great on muffs after going through that. I brought it to the lake and it would not start in the water, back home pulled top plug wire while running with no change at all, replaced and pulled bottom wire and it stopped running instantly. Checked spark again and had good spark, still have compression, plug was wet with a dark almost oily look to it. Also noticed fuel droplets spitting out of top carb when running, reeds looked good when I pulled the carbs off. Top carb also for lack of a better term "gasps" - if i put my hand in front of it there is a strong vaccum, then little or nothing, then strong vaccum. The bottom carb does not do this and seems to have little vacuum pulling my hand when I cover it. Pumping primer does nothing, primer bulb gets stiff. Pulled plugs in/on carb and cleaned behind them orifices clear. This is my first boat, and my first experiences with an outboard any advice or thoughts would be greatly appreciated.
Sorry so long

Josh
 

weekendfisher

Petty Officer 3rd Class
Joined
Feb 26, 2010
Messages
79
Re: 1971 50hp Johnson top dead on top cylinder

I had a similar problem on my 55 Johnson turned out the be the carb blocked up full rebuild and it was as good as new.
If you have aleady had the carbs off it won't not hurt the re build them
If you have spark and compression i'd be leaning towards the carbs
Cheers
 

eavega

Lieutenant
Joined
Apr 29, 2008
Messages
1,377
Re: 1971 50hp Johnson top dead on top cylinder

There are folks who know a heck of a lot more about outboards than I do, but I would venture a guess here; Perhaps a problem with your reed valve? The way I read it is, you have compression, but no vacuum. A reed stuck in a closed position would account for good compression (up stroke), but on the down stroke, when air/fuel would normally get sucked into the crankcase through the carb you get nothing.
Now, a reed valve is a fairly simple piece of the motor (basically a metal flap that has enough flex to be pushed closed), and from what I remember of actually seeing the reed plate once, its default position is open, so a reed valve stuck in a closed position would be unusual, but its something else to consider. I just don't see how a dirty carb would result in no air intake through the carb. Certainly, no fuel would be delivered to the crankcase if your jets were clogged, but air should still get through the throat of the carb.
I'm just venturing a guess here, and other folks please correct me if I am wrong in my deduction.

Rgds

Eric
 
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