1985 Evinrude 150xp Problems

New here, hopefully someone can help me out. I just bought a used boat for my son who is on the Bass fishing team at his high school. I went to look at it yesterday, heard it run, it was running a little rough and the guy told me it needed plugs, he told me that he replaced the power packs and they do look new. Bought plugs, check all to make sure they were firing...now I can't get it to start and run. Cranks fine and will hit every now and then and run for a second or two but that's it. Any help on what else I can try would be greatly appreciated. The motor is a 1985 Evinrude 150xp, Model: E150STLCOH. Thanks in advance.

What exactly is your starting procedure?

First... Trouble shooting basics.............

Spark plugs should be Champion QL77JC4 PLugs, gapped at .040

Remove Spark plugs. Check compression to be approximately 100+ psi & even on all cylinders. What psi reading do you have on the individual cylinders?

Plugs still removed. Check spark which should jump[ a 7/16" gap with a strong blue lightning like flame... a real SNAP! Note that checking the spark merely by using the spark plugs is a waste of time. The 7/16" gap is important! What result did you obtain?

If the two areas above are as they should be, the usual problem is fouled carburetors. However, you could also have water in the fuel...... or a sheared flywheel key if someone had the flywheel off and did not torque the flywheel nut down to its 145 foot pound specification.

Let us know what you find.

I'll get on this ASAP and get back with you, my work kinda hinders me from doing alot except on my off days so it may be wed before I can get back here. Thank you for the info.

Small update on this. I was able to check each plug for spark (removed and crank to check for spark) and found one to not have any spark at all. All but that one is like having a lighting show on the boat. I'm going to try switching one out with another to see if I can get spark there or not. If I get spark I'm guessing the coil pack is bad.

What exactly is your starting procedure?

Check spark which should jump a 7/16" gap with a strong blue lightning like flame... a real SNAP! Note that checking the spark merely by using the spark plugs is a waste of time.

You can swap the orange primary wires that lead to the coils to test for a bad coil.

So I go back today and recheck everything. All plugs are sparking...not sure where or what the problem is but I got some fresh gas and it fired right up, ran for a second or two then shut off. My battery wasn't up enough to restart it so I'm gonna charge it and try again tomorrow.

Engine must crank over at least 300 rpm in order for the stator to energize the powerpack.

Slow cranking engine..... you're lucky if it ever starts.

After charging the battery it started. Got a little miss in it but idled good. I removed the fuel tank, drained it and the gas that was in it was almost brown...gonna put it back tomorrow after I get it cleaned out and dried, fresh gas and take it to the lake. I'll let you all know how it goes Thank you for your responses.