Mark, how many hours on that block sence last rebuild? While you are getting the leak-down kit you might also pick up a new compression tester to verify your 105 reading.. I agree all cyl's showing that low compression and that close is odd.
When it was rebuilt were the stock heads reused? If there was a head replacement that could very well lower the compression across the board, also if a thick head gasket set was used it too will show lower compression.,
having said that, neither addresses your #4 plug fouling problem.
Many here know far more than i about motors but i am guessing a valve train problem on #4
let us know. Good luck and don't let the nuts and bolts scare you, nothing overly complicated in doing top end rebuild in your garage.

We'll I was having trouble finding tdc. For the leakdown, I think I know what to do now. We'll just before it got dark I thought I would try doing the compression again but the engine was cold, but I did open the choke my readings were much better. We'll try again tomorrow .

Mutch better, can you quantify?

Pull the plugs to turn the engine over by hand easier. Use the timing marks to find TDC for number 1 and follow the firing order turning the engine over 90*. Make sure it is on the power stroke. Getting it at the top is the tricky part without a degree wheel. Also, do it on a warm engine.

Compression test should be done with the throttle plate(s) wide open. Just a fyi on 4 stroke outboards if you leave the throttle plate(s) closed you could be surprised how low the #'s turn out. Just saying. I would redo it to see what takes place then move forward from there. Also how well or not does the engine run on the water ? can you achieve max RPM's underload ?

Guys thank for all the help. I just finisher the compression test again
1-130 had some oil around it but not bad
2-125
3-130
4-130. This was the plug that fouled out on me
5-130
6-120
7-130
8-125
Test was done with the engine warm all plugs out choke open.
As I was warming up the engine a little bit of water started to show around the intake in front of the engine. I am headed back out to try the leakdown. I know these numbers are still low, but they are better than before. Let me know what you think.

Thanks

I think your numbers are fine and #4 is sucking oil from somewhere. Should be a cheap fix. Start by pulling the intake and inspecting the gasket where it seals towards the lifter valley in the area of #4. No need to do a leak test on the engine with those comp numbers in my opinion.

Start by checking the torque on the intake manifold bolts. Don't quote me on it, but I seem to remember it being around 35 ft.lbs. If they are substantially loose, Replace the intake gaskets first and see what happens. Your compression numbers are awfully close to each other to really indicate a major problem. It would take something like the timing chain being off a tooth to bring all the numbers down equally, but it wouldn't run for $hit like that.

Two things when doing compression tests:

1) Fresh battery. Cranking speed has everything to do with how high your numbers get.

2) Carburetor / throttle body - wide open. As OP discovered, choke too. No air to the engine, nothing to compress. Note: smaller the cam (less overlap) the more this is important. But...it's super important on everything so always do this no matter what.

Also you will get different readings using brand X compared to brand z compression test gauges. We have seen brand X showing 105 psi compared to 130 psi from brand Z as an example.

Also compression ratio plays a part with the overall compression test #'s. fuel and or any water in the cylinders will always make the compression test #'s higher than what they really are. Also before doing any compression test it is always wise to disable any electric fuel pumps.

mercruiser recommends compression #'s to be a min of 100 psi and no more than 70% different in values from the your highest testing compression number compared to your lowest testing compression number.

Always open all throttle plates, chokes when doing a compression test.