Engine troubles, 1976 Mercury 850/85HP

[67Mustang-man]

So last weekend I had some issues of the engine bogging out at 2-2500rpm and at best 5-7mph I haven't had much time to really dig into the carb system on the engine, I have installed a new stator, trigger and regulator on this motor. Here is what is happening now, I sprayed some cleaner into the carb, blew out the jets and now I can get it to 4k and at best 25mph. If I push the stick I can feel it want to take off like the there is torque there but it will almost stall out if I go to fast. A slight fast bump will toss you back a bit but to fast it will stall, If I ease into it I can get it up to 10mph if I have someone sit on the bow seat it will get to plane and hit 25mph
Am I asking to much for this motor or could I be missing on 1 or two cylinders, it does have a bit of a rough idle but I don't know if this is normal for two strokes. With all the poor electrical issues these motors at this time were plagued with could it be bad coils? All I can be left to is coils or low compression.
Total weight boat plus gas gear and people 1500lbs the boat max capacity of people and gear is 1050, I am not sure if that means gas as well but with 1500 is everything and if you take out 617 dry weight of the boat that puts me at max. The boat is a 1976 Monark Mcfast 5 "Mcslow"

 

[Chris1956]

Let's start with the basics. Take a compression test and see if she has spark on all 4 cylinders. What prop pitch are you running?

 

[67Mustang-man]

I am going to the parts store tonight to pick up a compression tester, I also found the specs on the coils to see if they are good, the pitch of the prop is 19

How many PSI should I read on the compression test thats what I would like to know.

 

[Chris1956]

All four cylinders should be greater than 100PSI, and within 15% of each other. The total PSI is not important as the accuracy of compression gauges varies.

 

[67Mustang-man]

Okay, I picked up a Bosch cylinder compression tester last night I did not have much time to check them last night. I will hopefully get a chance to test them tonight and I will report back my findings.

 

[67Mustang-man]

Ok so here are my results, Compression is as follows 120 135 125 130 cyl plugs 123 looked a little wet n brown plug 4 was white and dry

 

[Chris1956]

OK, compression is fine. Sounds like you have spark to all as well. When you say spark plug #4 was white and dry, do you mean it looks like new, or does it have white ash on it? White ash can mean lean running. Like new can mean water infiltration, which is a common problem and could be all your issues.

BTW - 25 MPH at 4000 is probably not correct. Either the speed or the RPMs are inaccurate. I would think you would see at least 32MPH at 4000RPM.

 

[67Mustang-man]

Looks like new, not even an oily residue on the plug. With water infiltration wouldn't I see even oil on the plug, if it is water infiltration what could cause it and what would be the cure and how do I find out if that is what it is?

 

[67Mustang-man]

could this be a bad water pump gasket?