98 Mercury 15hp 2-stroke No start

[Miruton]

Hi, we have a 1998 Mercury 15hp 2-stroke.
I came across your forum and wish to ask you for some advice. I am fairly new to the boating world and just joined a group of friends that owns this sailboat. The outboard engine does not start. It used to run a few weeks ago but slowly started to die out once in awhile during our trolling. We took the carburetor off and checked the fuel pump (rubber diaphram and spring), cleaned the ports, adjusted the float level and put it back on and tried starting with no luck. Before we checked for spark, we took off the engine kill switch on the tiller because it was not working... made sure the other kill switch was in the run position. Replaced with new spark plugs...spark test ok.
Tried starting again but with no luck. Sprayed starter fluid into air intake after opening butterfly but still no start... Checked stator resistance, trigger, and coil/wires just to be sure... looked good within specs... as good as our old multi-meter.
Just running out of ideas. Changed fuel lines running from fuel inlet to fuel filter and from fuel filter to carburetor. Dont know how to do timing. Compression checked by just placing finger over plug hole.

 

[flyingscott]

Do a proper compression test. Make sure spark jumps 7/16" of a gap. The rubber gasket with the spring is not the fuel pump it is the primer. Was the motor pumping water?

 

[Miruton]

Hi Admiral,

Thanks for the reply. Currently waiting for a compression gauge and making sure on the spark plug gap. As for the primer and fuel pump...both were checked to make sure no tears in the diaphragm, springs were ok, ball bearing in place. Motor was pumping water (peeing) when it was running.

Do you know if timing is an issue in this type of motor?

 

[flyingscott]

Leave the timing alone it is mechanically set and does not go out. Unless something catastrophic happend or you adjusted it. The spark needs.to jump a 7/16" open air gap.

 

[Miruton]

Borrowed a compression gauge from O' Reilys and did a test.

Read 70psi at first, but second reading showed no pressure!! Thought the gauge broke or something. Re-tightened and still read only about 5psi. Did the test on the other cylinder and and same thing about 5psi. Arrgghh! Must be a bad compression gauge...

 

[Miruton]

Before starting our third compression test, we tried starting the outboard and much to our surprise the motor started. I did put in Seafoam into the gas tank before but..... Last week when we did the compression test I neglected to open the throttle and maybe led to the no compression reading. Could it be the seafoam dissolved some carbon build up in the piston rings? I was going to put some oil in the cylinder to help with compression but since the engine started, just left it idling for about 15min with seafoam in the gas tank.

 

[Miruton]

With a brand new compression gauge we read top cylinder 95psi and the bottom cylinder 105psi. Hope running Seafoam through the engine helps improve compression.