60HP Merc Dies at Full Throttle - Ignition timing possible cause or other?

Hello,

I just bought a boat with a 1994 60hp Merc on it. I knew it ran rough when I bought it but compression good.

After doing some work to it at home and checking on muffs ( work described below ) took it out onto the lake and seemed ok for 15 seconds at full throttle then rpms drop and engine stops completely. I am able to restart it afterwards with a little persuasion from the high rev lever. After restarted, engine doesn't have the power that it did prior to warming up. Also tried running at boat launch on trailer and started hearing engine ticking. RPM was limited since boat was on trailer at time, so could not develop full RPM.

I am wondering if the timing could cause the motor to stall like this at high enough RPM that the timing is so advanced that it causes the engine to more of less try and run backwards...

Here is what has been done to motor so far.

- running rough when first purchased, so gave it the Power Tune treatment with little change in operation.
- Removed carbs, took apart, and had them cleaned (soaked in Carbonex) at dealer. Also replaced float needle valve in bowls. visually checked reed valves from carb port for damage/ chipped valves - all looked good. Reassembled carbs and installed.
- Removed in floor gas tank, drained all old gas - wasn't gummy or dirty, and no water with fuel. Rinsed tank - very little debris. Reinstalled and filled with fresh gas.
- Replaced spark plugs
- Muff test revealed still running rough and Tach not working, along with voltage regulator ( no output voltage )
- While on Muffs pulled plugs 1 at a time, Cyl 1 no making any difference, checked spark with gap tester - jumps 7/16 gap no problem on all cylinders. Swapped coils from Cyl 1 to Cyl 2. No change - Cyl 1 still not making a difference in engine operation when plug wire pulled. Found that carb synchronization was out - carb 1 was holding carbs 2 & 3 open enough to keep idle higher by previous owner... Corrected and running smoother...
- Replaced water pump impeller and gaskets because i forgot to turn the water back on at 1 point and no water coming out of motor anymore on muffs- also blew out water lines/ water system to remove any debris in lines from worn impeller/ sand, etc.
- Replaced voltage regulator

- Took out onto lake for first trial at full rpm. - Hard to start - Once going seems to idle ok, but a little rough. Got onto step first time no problem, then motor RPM started to go down after about 10-15 seconds ( when i got to about 50K/Hr ) until engine completely stopped. Able to restart with high idle, tried getting back on step and engine is now lacking power - doesn't seem to want to break the 4000RPM, then dies down again - Thinking Fuel Starvation I gave the bulb a squeeze during the RPMs going down and bulb is not soft - RPMs did not increase at squeeze of bulb. Tried this a few times to make sure and tried a few carb adjustments ( a little leaner & richer on needle valve) with no success or change in operation.

-Tried at home on muffs and could not replicate same issue - did not want to over rev either under no load.
-Took out on second trial with new plugs in it with same results.( no spare plugs first time out since they were already new )
-Thinking its related to a loaded engine at full throttle, put boat on trailer at launch and started with motor in water there. Motor is always hard to start but seems to run OK when started. With it on trailer go full throttle and as expected RPMS did not go much above 3000 due to setup. but with load on it, started hearing a distinctive ticking once motor warmed up, but there was no power loss even once it warmed up. This has me thinking that it is related to timing - along with the ticking sound -

So this is where im at now... just wondering if this all makes sense or if i'm going down the wrong path here... Please advise if you have any more ideas or if you have been through this and have a solution.

Thanks ahead of time!!!

Best regards,
Eric

If it were my motor, I would go back to the carbs. Carbs are some the most mis-understood part of an internal combustion engine. They have two or three fluid flow circuits selected by throttle plate position and venturi effect differential pressure. The fact that your spark is good on all cylinders at low RPM and that it is hard starting, your carbs are not clean. Snake Oil (ie.. gas additive fuel system cleaner) is not a solution for an already gummed up carb, it may help it stay clean but will not undo already in place damage.

ALL the reputable marine mechanics in my area ultrasonically clean carbs and probe/clean very small port with a fine brass wires. It is not a quick process. I follow their lead at home with a 6 liter ultrasonic cleaner.



These are the carbs off my '86 Merc 60hp. They look like new inside and out.

Take it for what you think it is worth.

Thank you for the feedback FishinLite.

I will check the timing to confirm it is OK and then i will re-open the carbs and check them all again. I have another little boat in the mean time to get me on the water and catching fish...

Thanks again!