Inconsistent Cranking, Not Idling

[h7awaj]

Hi everyone! I have a Mercury xr120 120hp 1998 2 stroke engine that I have just brought recently. The owner told me that the boat was working fine, but due for it being stopped for more than 10 months, it would not start. After changing the fuel and doing multiple cranks, I was finally able to get the jetboat to work.

The only problem that I am facing, is that I am getting an inconsistent weak crank. The only way I got the boat to work is by using 2 fully charged batteries, and with only 3 plugs in. I was able to get the boat to work with all 4 spark plugs attached, although it would not stay turned on if I leave it on idle.

What could the problem be? I would appreciate your help.

 

[alldodge]

The cranking over slow is the battery, starter or wire and their connections. The starter can be one of two models.
http://www.mercruiserparts.com/120xr-powerhead-1998-0e315905-thru-0

For it not to run very well, suggest starting with compression test and carbs. My guess with it being able to run with only three plugs in is either low compression or the plugs are firing at the wrong time

 

[h7awaj]

The cranking over slow is the battery, starter or wire and their connections. The starter can be one of two models.
http://www.mercruiserparts.com/120xr-powerhead-1998-0e315905-thru-0

For it not to run very well, suggest starting with compression test and carbs. My guess with it being able to run with only three plugs in is either low compression or the plugs are firing at the wrong time

How should I check the timing and adjust them? I have seen in several websites, but I did not understand it well.

 

[ondarvr]

Don't worry about timing, get the carbs and fuel system clean, plus like already mentioned, check all electrical connections and the starter itself. Being able to run on three cylinders would be normal.