Water in fuel or something else? Warning. Long read.

[flakeys2005]

I have a 1987 Wellcraft St. Tropes 3200 with twin merc 350's. I have been topping off the fuel tanks after every trip to get an idea of how much fuel I'm burning. We were not running the engines at more than 3000 rpm for the first few trips at the advice of the previous owner as a measure to save fuel. The problem with that is we were not getting on plane, so at the advice of some fellow boaters from our club, we opened her up to get on plane and hopefully save fuel by not plowing through the water. On our way to Block Island from Watch Hill a few weeks ago we opened her up, got on plane but ran the port fuel tank empty. As the remaining fuel was sloshing around the rpms started to surge and the port engine steadily lost power. We put fuel in both tanks upon arriving in the pond and enjoyed several days at anchor. Returning home she ran great all the way to the mouth of the CT. River where the rpm started to surge again and I limped her home on the starboard engine. Once back at our slip I changed both fuel/water separator filters and ran the engines for several minutes. This past weekend we went to Mystic Seaport and she ran great all the way to the mouth of the Mystic river where we encountered the same problem. Once we arrived, I drained the filters and hoped for the best. The trip home was about the same.
It seems as though my problem started after the first time I really opened her up, or maybe after I ran the port side dry, or after I run her for two to three hours. I'm stumped. What do you think might be causing this problem?

 

[hivoltg]

Re: Water in fuel or something else? Warning. Long read.

When the port motor starts acting up, does it just surge at high rpm or does it sputter and die?

 

[achris]

Re: Water in fuel or something else? Warning. Long read.

Still waiting for the 'long read'....

Given that the problems started with the running down of a fuel tank it is possible the events are related.... However, that might have just uncovered a deeper problem, or might just be a coincidence.

With these sorts of problems, I like to drop back to basics and start afresh as it were.... Assume nothing...

This is a generic list I use....

1. Compression tests.
2. Check spark plugs, replace if needed.
3. If points, replace, along with condenser and rotor. Check and adjust, if needed, points cam dwell angle.
4. Inspect distributor cap, rotor and leads, replace if necessary.
5. Check spark quality (needs to be a nice BLUE spark drawn over 1/2").
6. Set timing. Check timing advance is working correctly.
7. Check/change fuel filters and check that the fuel system is not sucking air.
8. Check fuel pump pressure.
9. Check for full opening of the carb. Also ensure choke is opening fully when the engine is warm.

Once I'm happy that the engine side of things is right, then I move on to specifics....

Surging is a nasty. Could be ignition, could just as easily be fuel.... I know from my own experience that old spark plugs are a good culprit for that too on GM engines....

HTH,

Chris.......

 

[flakeys2005]

Re: Water in fuel or something else? Warning. Long read.

When the port motor starts acting up, does it just surge at high rpm or does it sputter and die?

I basically lose power while it is surging, but it continues to run. The first time it happened going into Block, I was sure it was because we were near the end of our fuel and we were sucking in water from the bottom of the tank and possibly air too. The next time it happened going into Mystic I figured the new separator had filled with water and that was causing the surging, though I was surprised it would fill that fast. When I emptied the filter at mystic, it had some water but not half. Then on the way home, it seemed like a coincidence that the timing is always about 2.5 hours before it happens. That, in fact, is why I still believe it is fuel related. If it were timing or ignition, I don't think she would run so great for so long before surging. Thanks for reading and giving some thought to my problem.

 

[flakeys2005]

Re: Water in fuel or something else? Warning. Long read.

Chris,
After reading your list one thing occurred to me and that is my starboard packing nut is a bit loose and has more of a steady drip while docked than 4-5 times a minute. While I am under way, I'm sure that steady drip is more of a heavy stream and with the rotation of the shaft, could it be that I am splashing water all over some electrical component, causing the ineradicable behavior? Maybe the distributor cap or wires. Hmmm. What do you think? Does that sound feasible or am I reaching?

 

[achris]

Re: Water in fuel or something else? Warning. Long read.

Chris,
After reading your list one thing occurred to me and that is my starboard packing nut is a bit loose and has more of a steady drip while docked than 4-5 times a minute. While I am under way, I'm sure that steady drip is more of a heavy stream and with the rotation of the shaft, could it be that I am splashing water all over some electrical component, causing the ineradicable behavior? Maybe the distributor cap or wires. Hmmm. What do you think? Does that sound feasible or am I reaching?

Seawater? Definitely. I had an engine shutdown in heavy weather once ... All I could put it down to was seawater splashing on the shift plate (shorted the interrupt switch, killed engine...)

 

[flakeys2005]

Re: Water in fuel or something else? Warning. Long read.

Ineradicable???
I hate auto spell check sometimes. I spelled erratic.

 

[Another retired guy]

Re: Water in fuel or something else? Warning. Long read.

This sounds similar to a problem I had recently. Runs fine for a while, then starts losing power. First suspect was gas - but after eliminating that I discovered that the coil was arcing from the HT lead to ground! Cleaned up the connection and problem solved. No idea why it was intermittent
Next time you have this problem, open the engine hatch and look for sparks. Rev the engine as sometimes they run fine at idle.

 

[flakeys2005]

Re: Water in fuel or something else? Warning. Long read.

This sounds similar to a problem I had recently. Runs fine for a while, then starts losing power. First suspect was gas - but after eliminating that I discovered that the coil was arcing from the HT lead to ground! Cleaned up the connection and problem solved. No idea why it was intermittent
Next time you have this problem, open the engine hatch and look for sparks. Rev the engine as sometimes they run fine at idle.

Thank you. I will check that out, though it is difficult to remove the floor while under way.