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2000 50hp running rich.

S

Shearpin2

New member
Mercury 50hp 4 stroke

Model 50elpt

Year 2000

Ser# G962081


I don't care how long anyone has been turning wrenches on marine engines. At some point you come across at least one(1) problem child, and it can have you pulling your hair out. This one is mine and my 35+ years of working on All makes I'm just at a lose and looking for some help . Turning it into an anchor is not the answer.

2 months ago test running the engine, I found it to be running rich. It would foul plugs with in a hour. Seals on the idol jets still untouched.I went threw all the carburetors , cleaning every fuel and air port, nothing left untouched. Even removed the sealed idol jet, for a cleaning. Yes a counted the turns of the jets recorded everyone . Even as a mechanic I had to say “ damn these carb kits are expensive”. And before you say adjust the float level, these floats aren't adjustable. It's a set and done.

With vacuum gauges set , I've tuned the carburetors . It runs rich, tweeked the idol jets, it runs rich. I started thinking about the vacuum diaphragm accelerator pump. But mercury/aftermarket doesn't seem to cover this item. No means to test it's operation. Hooking up a make shift 4 into 1 vacuum manifold to a vacuum gauge and operate it the needle shows about 1gh of vacuum that dissipates in a heart beat. I'm thinking this system could be the cause for the engine running rich. On top of it finding a replacement part is NLA. Buying a use part, isn't real an answer, because how long till that fails? I wait for your reply.


Shearpin
 
Follow the carb bowl vents, they gang together into a rubber tube that exits front of motor pointing down. It's sort of above & if I recall correctly just behind the tilt tube.

Gets plugged up with insects & debris & float bowl(s) doesn't vent.
 
Hey shearpin,
Sounds like you're loaded for bear and have your gray matter deep into this... Have you verified engine temperature, cold shows its ugly head as rich. Does the engine have the correct spark plug heat range? Have you verified compression? Spark with a real spark tester? Just the basics...
 
Chocking over the rich fuel, engine came up to 140-150 in 5-6 mins. Still running rich. I removed the thermostat and the thermoristor ( two wire gray with black strip, and black wire.) pretty piss poor description in the manual what it does. My experience is screaming this is a ets for the micro- processor.
Tested thermostat opens right around 140. Using that info and letting the water cool , I used the thermostat as a temp guide for water temp as I tested this thermoristor sensor with OHMs.
Cold water meter have a reading of OFL.
holding it just part of the sensor below the water surface, keeping the wire above the surface. Hooked up to the meter I saw the stay at OFL until the start started opening. The reading when just like this:
OFL
26 45
28.90
30.10
OFL
24.67
34.23
OFL
36.54
38.71
27.56
39.01
OFL
45.34
32.33
23.34
At that point I'm saying this sensor is shot. It's jumping all over the place ever second it not holding steady at all. Mercury claims this is just a over heat sensor, but under Yamaha manual it feed resistance temp for the micro- processor to control ignition timing.
Mercury list the part NLA
YAMAHA HAS IT AT $114.00
Same wire colors, same connection, same place of connection going to the m.p.
 
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