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1983 Mercury 70 HP stalls under load

Emerson2

New member
I have a 1983 Mercury 70 HP that stalls under load. It is getting very good spark at plugs. When I pull number 3 wire it has no effect on how the engine runs. When removal of plug there is a wetness on plug.Engine runs rough. Why in the number 3 piston not fireing internaly? Can someone help me?

Thanks,

Emerson2
 
Last edited:
What is the compression on the # 3 cylinder ??------------Have you checked the reed valves for # 3 crankcase.---------------------Have you checked the lower carburetor for a blockage ( no fuel to # 3 )
 
I now am not sure if it is cylinder1 or cylinder 3 but it is the bottom cylinder. Yes I did check the compression and it is top cylinder is 141, middle cylinder is 149, and bottom cylinder is 141. I have not checked the reed valves. not sure where they are.
 
The top carburetor feeds the top ( #1 ) and also #2------------The bottom carburetor feeds #3 and also #2 ------------So there may be something wrong in the bottom carburetor.-------------------The reed valves are internal around the crankshaft.-They can be inspected when carburetor is removed.
 
Well I got time to work on my engine. Removed carbs, removed the bowls , checked everything and they are clean and look good. I did find the reed valves. They look good, but what I am I looking for? I did order a new stator because the insulation on the wires have started break and wires have corroded and starting to break. Where do I go from here?
 
Laying plugs on the block is---------- NOT A GOOD TEST FOR SPARK------------------See/test what gap it can jump!!
 
Tomorrow I will put some of the parts back so I can check the spark with an ajustable spark tester. I will let you know what I find.
Thanks,

Emerson
 
I suspect you have a bad coil. If # 2 runs okay, then there's nothing wrong with the bottom carb.

Jeff

PS: I run one of those myself and like them (which is not what most people think of them!)
 
The one and only motor of this type I ever saw had broken reeds and was doing the same thing. You have to split the cases to fix it . also you can't see all of them without spitting the cases.
 
you can also get a spark tester, plugs in line between your plug wire and your sparkplug, it will light up if you are getting good spark.
 
racerone

I thought that I sent this yesterday. Well I will try thios again. I put this motor back together enough to start. To my surprise it started and ran very well. I did check the spark gap with a spark tester. Opened the gap to about 1/2 in. and I have a very heavy dark blue spark on all three plugs. Not sure what I did but it seems to run great. Maybe the float valve was stuck or dirt in carb. Next i will put it all back together an d try it on the lake. I will make final adjustment to carbs there. Do you think I should do anything else.

Thanks for your help and support

Emerson2
 
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