1986 Mariner 45 hp 4 cyl. 2 stroke idles great, dies after 3 minutes on plane

[eatbreathesleepbass]

Hey all, Im hoping you will be able to help me solve my issue that I'm having.
I inherited my dad's old 1986 Grumman bass boat from him 2 summers go. It's got the 45hp mariner on it and it ran like a champ the last 2 summer until late August last summer. I was cruising along and the motor started "surging" by surging I mean that it revved up then down multiple times before I lost half of the power (top 2 cylinders quit firing).
Fast forward 5 months...it has a new stator, trigger, switch box, and spark plugs. Had the carbs worked on at a shop and it ran again for about 5 trips before it went back to what it did above. Took it to another shop that specializes in merc/mariner motors, they claimed to adjust trigger linkage, work on the carbs, and lake tested it claiming all was well, charged me $250 and away I went.
Got to the lake Saturday, fired right up, docked it, parked my truck and hopped back in my boat. It got up on plane beautifully and cruised right along for all of 3 minutes before surging again and dying. Back down to 2 cylinders I went...limped it to shore, used my trolling motor to fish back up the shoreline and fished on the way back to the dock. Only plus side of this trip was I caught a nice 3.5 pounder on my first trip to the lake this year.
Anyways, I am at a loss. I've spent over $1,100 on parts and labor since august and have nothing to show for it. PLEASE HELP!!! I must get back on the water!
Thank you ahead of time!

 

[DavidMoore]

My engine used to show similar symptoms, would continually stall out one day then be fine the next.
I spent a couple of hours and rebuilt the fuel pump, replaced fuel filter and all the fuel lines from the tank to the first carb, installed a new primer bulb and orientated it so the arrow was pointing upwards (can make a big difference, if only when priming).

Don't really know which one of these fixed the problem but it's never missed a beat since.

 

[eatbreathesleepbass]

The shop has informed me that the trigger linkage was incorrectly hooked up, causing the timing to not advance when throttle is applied. They will be taking the carbs off later today to see if the jets are clogged from old debris in the gas. They say gas lines and primer bulb are ok, but i think I am going to change them out anyways. It certainly wouldn't hurt. As of right now, they still don't know exactly what the problem is.

 

[Texasmark]

My grey (silicone ???) OEM line started shedding at 10 years, as did the internal hoses...you are old enough on that rig to redo all the rubber. Just stop, bite the bullet do it all and be done with it. Money and time spent are just that....spent, gone forever. What you have in front of you is the possibility of worry free boating.

 

[jimmbo]

You said you lost the top two cylinders? You verified it was ignition and not a fuel starvation? I ask because it has happened more than once, and after ignition parts were replaced. When it acted up did you check to see if the fuel tank was vented. The top carb is most likely to lean out first.

 

[444]

When it starts surging, check the primer bulb. If it's sucked shut like a kid on a juice box, you have a fuel tank or line problem. If pumping it makes the engine come back to like, you have a fuel flow problem. Has nobody replaced the fuel pump diaphragm on it?

 

[Silvertip]

Are you using a plastic portable tank? If so, empty it and then take a peek inside. Check for plastic debris from the drilling and finishing operations when the tank was new. That debris can clog the pickup screen. Ask me how I know this. Out of curiosity, I frequently peek inside brand new tanks in stores that sell them and very often I find debris inside them. Although the primer bulb may not suck entirely flat, the tank restriction can affect engine operation. If fuel delivery is a problem then stop running the engine until you find the cause as lean mixtures is what destroys most two strokes. Bad carburetor repairs and bad fuel pumps are high on the list as well.

 

[eatbreathesleepbass]

Thank you for all of your input, I went ahead and replaced all fuel lines and such once I got it back from the shop yesterday. My issue was a combination of ignition and fuel starvation. The trigger linkage as stated before was not put in properly so the timing would not advance. The shop also found (the second time I had it in) that the top carb was being starved of fuel, so they took the carbs off and found that the diaphragm inside the upper carb was imploded on itself, causing it block and fuel from flowing through it into the motor, thus meaning the top two cylinders weren't being fed fuel. Now i'm waiting for a warm day to take it out and give it a try!