84-90 9.9 Force ignition issue

I'm new to this outboard motor scene. Normally I work on cars and trucks. I bought this motor, which I was told was a 9.9, for my aluminum boat. The model number on the US Marine tag shows 152y9a and the serial is 1050. The lower cylinder had no spark. I soaked the carb and blew it out w/air and checked the float adjustment. I cleaned the points and replaced the dead cylinder plug wire,due to hole in wire, and installed new champion plugs. Excellent spark from both cylinders now. Checked continuity and resistance of both coils w/nearly same result on both. The engine still only fires on the top cylinder and the bottom plug stays wet w/fuel. I have swapped condensers and spark plugs from one cylinder to another w/ the same result. Compression check yields 116 psi top cyl. and 112 lower cyl. I pulled the head off and the gasket looks great and the cylinders have very minimal carbon build up. I should mention that it ran on both cylinders for nearly 30 min. in my test can 2 weeks ago and when I went to start it 3 days ago it was running on only the top cylinder again, but there still is great spark to both plugs. It doesn't appear there is any water leaking into the lower cylinder. Any help would be appreciated.

Re: 84-90 9.9 Force ignition issue

The coil that had that bad wire must be leaking. It probably had to work real hard and might have created a path with less resistance between the windings and laminations. It could fire a sparkplug out in the open, but compression increases resistance at the gap and the juice is probably finding it's way through that leak instead.

Re: 84-90 9.9 Force ignition issue

Thanks Willy. I have heard some things about a reed valve. Any thoughts? I have ohmed out both coils and they are similar, but I will look into getting a replacement. I am pretty sure I found one at boatingsolutions.com for $48. Have you seen any cheaper? Thanks again.

Re: 84-90 9.9 Force ignition issue

Yeah, their magneto parts are pricey! First, do you have an inductive pick-up timing light? You can test each half of the magneto while the motor is running. Just clamp it over either sparkplug wire. If the light flashes, the sparkplug is firing. If it's intermittent, you can usually see it (and hear it). I tape the trigger shut so I can drive the boat and just have to look at the light.<br /><br />When a coil starts to leak like that, it just burns a hole through the plastic. It won't affect the resistance unless it's been arcing for a long time.<br /><br />Maybe a reed valve, but they either work or they stop working forever (no coming and going).

Re: 84-90 9.9 Force ignition issue

I swapped the coils and points around and have the same thing. Missing on the lower cylinder and the plug is wet. I pulled the motor and pulled the reed valve assembly and it looks like they all seal very good. The fuel pump diaphram looks good and seems to seal o.k. What could be left???<br /><br />thanks for your help.<br />Chris

Re: 84-90 9.9 Force ignition issue

What is the compression on each cylinder?

Re: 84-90 9.9 Force ignition issue

Check the fuel pump diaphram, if it is leaking it will flood lower cylinder.

Re: 84-90 9.9 Force ignition issue

Before I disassembled part of the motor including the fuel pump, head, and reed plate, the compression was 112 lower and 116 upper. I have a new head gasket,reed plate gaskets and fuel pump gaskets and diaphram on order. The fuel pump diaphram looked good. The reed valves also looked really good.<br /><br />Thanks,<br />Chris