91 50 hp force compression?

I have a 91 50 hp force engine, model number 507P91A,
It will not start. I have changed the plugs and the coils. Apparently the new coils are grounded by bolts. The old blue ones were wired. I would like to know what the compression should read on the cylinders. I've taken the plugs out and noticed there is a spark on both cylinders when the plugs are out and it is a nice blue spark. It also turns over faster with the plugs out. I'm wondering if it's an issue with the battery not turning the engine over fast enough or am I losing power somewhere in the circuit? Is the battery powerful enough or Maybe it's a blown head gasket. One day it was cranking fine and later just a sputter. I'm new at boats and outboard motors. I do have lots of experience with my old Fix On and Repair Daily A. K. A. Ford truck. Oil changes, filter changes, brake jobs, Serpentine belt replacement as well as a few timing belt changes. (they used to be chains) I don't even know where to look or what to look for when I hear flywheel key or pack or cd.
But the nearest shop is an hour away so I need to become familiar with this engine if I want to fish further away from the dock. Thanks for your time fellas.

Re: 91 50 hp force compression?

Compression should be around 120 psi I think maybe Frank will will have the exact numbers. It should definitely be over 100 psi (it'll run at a 100, but you'll be losing a lot of power), and should be within 5 psi of being the same an both cylinders. this motor really doesn't have to turn over real fast to start if it's firing like it should and when it should , I've stared mine with a pull rope when my battery died. (Flat top non gap plugs should be used) It spins faster when the plugs are out because there's no compression building. these are, contrary to what some might say, really good little engines. the one I'm rebuilding is my second, when everything is right they start almost immediately every time the key is turned, cheap to maintain, and cheap to repair. Good quality parts can be found here on Iboats, at good prices, and used parts can generally be found on Ebay, Generic versions of some of the electrical parts (rectifiers) can even be bought at napa or radio shack.

Re: 91 50 hp force compression?

Thanks cadet.
I'm new to boat engines but there is beauty in simplicity and this really is a seemingly simple engine to work on.