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1978 50 Horse Merc Problems

J

Jonathon123

New member
Hi all. I am hoping someone out there can help me.

I am fixing a 78 50 Horse Merc. 4 cyl.

The problem started last yearon the water. Motor would run for a few seconds then die instantly only way to keep it running was to pump fuel in via fuel line. Ignition spark is strong on all plugs, compression is 120-125 on all 4 cylinders. I removed carbs and the bowls were full of fuel, floats appear in good shape, needle valves appear to be working and moving, I cleaned the carbs completely and replaced fuel pump diaphragms. Now when i start it it runs at high speed only and is very difficult to start. Once i finally get it running it will only run at 1/2 to 3/4 throttle As soon as i back off the throttle the motor will die.

I am hoping its not crank pressure issues...

thoughts anyone???
 
not one of the fiber mesh gaskets its a rubber one.i installed the new ones in the exact order that the old ones were installed and i was left with a gasket for each carb left over. So i assume whoever changed them before me also forgot a gasket in each carb.
when i first got the boat it ran fine for 3 outings last year and then on outing number 4 it started acting funny this was before i started any work on it, primer bulb had to be constantly squeezed until the boat was atleast at half speed (this was while it was in the water last year) . After i put new fuel pumps in it it will not idle at all it will just die unless its at half throttle and even then its finicky.
 
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Re visit the fuel pump,it's possible one of the gaskets is back to front?
The kits are made up of parts for several different motors,so spare bits are possible.
 
im gonna revisit the carbs. I actually have a proper diagram of how the carb goes together this time so hopefully it fixes the problem. Im wondering if its not a carb problem could it possibly the crankcase ???
 
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