Mercury 850 Outboard Trouble Starting

[62NewBoater]

Hey everyone, this is my first post here so please take it easy on me. I might be new to this but I’m willing to learn and take criticism.

Boat/Motor:
I have a 17 ft boat with a Mercury 850 2 stroke outboard built sometime in the 70’s (I haven’t found the SN yet.)

Problem:
When I first got it last year I was able to take it out a couple times. Other than some trouble initialing starting it ran okay. The last time I took it out last year the engine was cutting out toward the end of my trip. I would be able to get it going again if it stalled but if I hit the throttle too much the engine would start cutting out again.

I winterized it after the last trip and figured I’d deal with it this year.

So I’ve been trying to get the boat running the past few days and it won’t start. I can hear it clicking and moving slightly but it’s not turning over.

Here is what I’ve done/do:
-use 91 octane non-ethanol/ with 50:1 oil mix
-check fuel filter: doesn’t seem dirty or clogged (not sure if I know what I’m looking for but I squeezed a few times to see fuel flow when disconnected)
-check carb and cleaned, didn’t see obstruction using flashlight around the valves. I DID notice what looked like some gas at the bottom of the area where the carbs face toward the boat.
-I saw some broken plastic piece off the plastic piece connecting the two carbs, I’m not sure if that part is bad. I have a picture below of it.
-checked plugs although I’m not sure how to know if permagaps are bad. I did replace two that looked somewhat dirty near where I think the spark generates.
-using freshly charged deep cycle marine battery with cleaned connectors.

May I ask what I should be looking for next?

thank you in advance for your insight!

Regards,
Chris

 

[bugelingkayaker]

i would suspect dirty carb or fuel leak somewhere. "starting and then stalling under throttle" is common symptom of a cylinder not firing.
easy way to test if this is the case:
get it running, and while wearing heavy gloves and using pliers with rubber grips (to avoid getting a bit of a shock) pull the spark plug "boot" off disconnecting it from the spark plug itself on the top cylinder with the engine running. you should immediately hear the rpms drop. the motor might die completely. thats okay if it does. turn the engine off, reconnect the boot.
start the engine back up and do the same thing with the spark plug on cylinder 2. you should hear the same thing happen. repeat this on all 4 cylinders. if you disconnect one of the boots and theres no change at all, that means that cylinder wasn't firing, and if thats the case DO NOT RUN THE ENGINE for any length of time until you figure out what the issue is or you risk damaging that cylinder.
i'd also recommend a compression test. some shops i found will do this for free or you can pick up a compression tester from auto store for like $30 bucks. advanced auto near me actually does free tool rental on those so i didn't even have to buy it. compression on each cylinder should be within 10psi of each other.
also you said you cleaned the carbs, did you remove them completely from the engine to clean them? did you remove the idler screws from the carbs to clean them? if you did and didn't get them back exactly in the position they were in before, they may not be delivering the correct amount of fuel, which can cause a cylinder (or more) not to fire.