Mercury 50 HP not running to full speed?

[JoshOnt]

Hello everyone,
I have recently bought a "new" to me boat and when I test drove it with the guy we got up to a decent speed with 3 people in the boat but when I went out yesterday with only one passenger I could not get even close to the speed we got before.
'65 Scott boat v-hull
'77 Mercury 500 Series 50HP
19" prop
I have 6 gallons of gas in the back along with battery and a bucket with some light supplies (rope, extra cleat, 2 fenders).
The boat is fiberglass so not super light but not heavy.

If anyone had an idea that would be very helpful and thanks in advance for the great replies I hope to see.

 

[oldman570]

Re: Mercury 50 HP not running to full speed?

You need three things to happen for the motor to run to its best. Compression, Fire, and Fuel. Start by doing a compression test and record the readings. Then check the spark on each cylinder with a spark tester or timing light to see if your getting spark to the plugs. After that reply back and we will be able to help you more.
Oldman570

 

[JoshOnt]

Re: Mercury 50 HP not running to full speed?

This engine has a brand new starter and spark plugs, I had it put in because I like my engine to start first time, every time. As for the compression, have not tested it but I know it is good because I had it at D.C. Marina in Kingston Ontario less than a week ago for full engine check and they said everything was good and listed compression as "great".