650 merc loading up

[Tanner1995]

I've got a 65 horse mercury (I believe 1971) on my 15 foot thundercraft tri hull. The motor has new battery, new plugs, new starter, fresh gas, clean carbs, 125 lbs of compression in all 3 cylinders, good spark on all 3. It runs good on the trailer but as soon as Its in the water it's got nothing. It'll get up to about 7 or 8 mph and then load up and if you try to give it any it'll bog and die. My last guess is too much prop? It has a 10 3/8 x 14 pitch prop. Any other suggestions??

 

[merc850]

What's the serial Nr.? It sounds like a fuel pump/filter or line problem, if you pump the line bulb while accelerating will that solve the problem? The only way to find out if the prop is wrong is to install a tach but the prop you've mentioned sounds like its pitch is too low for a 15' boat, I would guess that it should be more like 19" or higher.
Set the low speed needles at 1 1/2 turns out from seated - then in the water underway at just above idle turn them out or in slowly until the motor runs smoothly; then try accelerating quickly and if motor bogs turn them out some more until it takes off.

 

[jimmbo]

If it is a 1971 or older it be would a 4 cylinder, which came from the factory with 2.3:1 gearcase. When you cleaned the carbs, you accessed all areas by removing plugs and domed caps? Are the carb floats set correctly? What did you set the mixture needles at for initial setting? Also, did you do what is known as a link-and-sync? It establishes that the timing and carb openings are properly synchronized.

 

[Tanner1995]

I haven't done a link and sync, never even heard of it is there any way of checking that's it's properly synced? And the fuel filter is new. Can't remember off the top of my head what i have the needles set at. I've had the carb off numerous times haha its been on ongoing problem now for a couple years.

 

[jimmbo]

Here is a link http://162.144.28.33/lib/mercury/man...-115.html#/220
If your engine is a 70 or 71 the pages you need to read start at 6-15

Other specs are at the back of the book

 

[aaronbell6863]

Where is the serial number located on your boat?

 

[racerone]

The 3 cylinder was first marketed in 1972.-----Open up the low speed mixture needles 1/8th turn at a time.----Simple procedure that often solves the bogging / stalling issue on the Mercury inline motor design.----Done it many times.