Mercury 200 20HP won't stay running

[foundryfishing]

Hey guys,

First time poster. First time boat owner.

Here's the scoop. I picked up this fishing boat from a friend of mine. It has a 20HP Mercury 200. I believe it's a 76' model.( Serial is 4407153 ) He hadn't owned it long, but had been using it for the last month or so. It had just been serviced a few months ago, and it was running fine until he refilled the tank. Then he couldn't keep it running (wouldn't idle) and decided he didn't want to mess with it. That's where I come in.

Seeing is how it was running fine before he refilled it, I started by just trying fresh gas/mix. No dice.
I checked the spark with one of those gap-able spark testers. Blue spark with a fairly large gap.
Changed the plugs just to be sure.
I checked the fuel line, it appeared to be disintegrating. So I replaced that, primer and all.
I took the carb off, cleaned all the jets, cleaned the bowl, ect.
Still no luck.

Basically I can get it to start with a quick shot of starting fluid. Which I know isn't good for these engines, I just wanted to confirm it would run. It will start and run momentarily and sometimes it will even run longer at higher RPM's. It definitely will not idle though.

So I'm just wondering what my next step is. I'm thinking fuel pump/carb rebuild, but again this is my first outboard.
Any help would be much appreciated.
Thanks!

 

[foundryfishing]

A follow-up on this. I got it running after going through the carb again. Took it out to the lake once. It ran totally fine. Took it out a second time, it had a miss and was running kind of rough. So I rebuilt the fuel pump with new gaskets. It was running great. So I decarbed it using the gallon of gas/seafoam method. It ran strong for the entire decarb.
I took it out to the river and was motoring up it for about 5 minutes running great... suddenly it just dies out. I try to start it and it'll idle momentarily then kind of backfire and die. I got it back home and started it up(running rough). Pull one plug wire at a time and it seemed like only one coil was firing (died when I pulled one wire, and didn't when I pulled the other). So I replaced both coils today. It's still running rough. When I do get it started it has difficulty idling. 9 times out of 10 if I try to throttle up it just kind of sputters and backfires.
So I'm wondering if this could be a float issue. The plugs are wet with fuel when I check them. I know they are getting a strong blue spark. I'm just at a loss here. Running 100% gasoline 50:1.

Any suggestions would really help. Thanks!

 

[CharlieB]

Two things.

A water separating fuel filter is highly recommended to ensure any possible water contamination of the fuel stays out of the carbs. Drain and flush the carbs again.

Spark testing must be done while MOVING the trigger/throttle throughout its range of motion. Trigger wires can break, losing connection during movement. What may appear to be a fine spark at idle may not be at all once the throttle is moved. Make sure.

 

[foundryfishing]

So I tested the spark again, the bottom plug is not firing. I traced the wires to the black box on the side and they're super corroded and exposed. Is it possible to open the box and rewire it? Or do I have the pleasure of dropping mucho dinero on a new system. Thunderbolt ignition btw.
Thanks

 

[foundryfishing]

Am I correct that the CDI is the main wiring center I'll need to replace?

 

[foundryfishing]

No Title

I got the new wiring installed. Seemed to be running great again via the storage bin I use to test it at home. Got it under load at the lake and it doesn't want to throttle up. If i feather the throttle will momentarily act like it wants to take off and then sputters out.
I'm going to check my float height one more time.

Also I rebuilt the fuel pump early on into this project. The kit I ordered came with two identically shaped diaphragm pieces. One looks like band aid material almost and the other is black rubber. I used the band aid looking one since that's what was on the pump when I took it apart. Does anyone know why the kit comes with both and if I should've used the other piece instead, or in addition? The carb diagram only shows one in being used.

This motor has been a real head scratcher so far..

 

[60sboater]

Try replacing it with the black one and retest.

 

[foundryfishing]

Try replacing it with the black one and retest.

We'll I tried swapping for the black one... no dice. I adjusted the float to 1/4 inch from the base and it seems like it made the problem worse. And since doing so it's super hard to pull start unless I have the throttle wide open.

One thing I noticed is the coil for cylinder one isnt sparking as easily as cylinder 2. With the plugs out, using my spark tester, I can easily generate spark for cylinder 2. For cylinder 1 it will still spark blue, however its not a frequent nor as easy to achieve. Both are new coils. New CDI. Tried swapping the plug wires, no difference. Could the trigger cause this?

 

[60sboater]

IDK if it's trigger-related. With an inline spark tester,you can see if a plug fires under the load of compression or running. I have both types of testers.

On another site,there's a controversy over which diaphragm to use or possibly both.

 

[foundryfishing]

No Title

Gotcha! Yeah I remembered reading something about the pump diaphragms on another site, but I couldn't track it down again.

Also, do these coils need to be grounded individually? I'll attach a pic. Where I'm pointing is where it was grounded initially (yellow connector wire attached to coil currently). I tried grounding it to the coil, but it didn't seem to matter.

 

[60sboater]

As long as your ohm meter shows both are at ground,it's good. Your wires have tape around them,how bad are they? Make sure 1's coil ground is as good as 2's and the internal contact is in good condition.

 

[foundryfishing]

As long as your ohm meter shows both are at ground,it's good. Your wires have tape around them,how bad are they? Make sure 1's coil ground is as good as 2's and the internal contact is in good condition.

I'll test the coils to make sure. They are new so hopefully I didn't get one that's DOA. As far as the plug wires, I taped them just as a precaution. I also tried swapping the one out of the coil that is definitely sparking well to the one that's not as hot. It didn't make a difference.

I got an inline spark tester today so I'm going to test again.