Gradual power loss, then it wouldn't run....

[berth control]

1985 170 mercruiser engine. Carb. and mechanical fuel pump. Recently replaced plugs, cap, rotor, wires, adjusted timing, cleaned fuel filter in carb. and cleaned the carb. Checked compression last week, all were at about 120, so good.

I was cruising back from a trip yesterday when about 20 miles in I started losing power on the stbd. engine. It went from 3500 (my normal cruise) down to about 3000, 2900, 2800, I gave it more throttle to adjust and it did not do much. Temp. was good, oil pressure good, other engine running fine. Pretty soon I could not maintain plane and had to come down to idle. Then the engine idled in neutral for a bit until I went to rev it up and it died. Would fire but not restart. At one point I got it to start up and fast idle at about 3,000rpm's, but would not idle or let me put it in gear.

I got back to the dock and backed into my slip on one engine (pretty impressed with myself for that, I was better than my neighbor with twins:grin. I started to tell the guys at the dock about what happened and went to show them what the engine was doing. It started right up and seemed to run fine. I could not put much load on it since I was at the slip, but it would rev up good and I could idle it and put it in gear no prob.

I think the mechanical fuel pump is weak and when it gets warm it does not pump like it should. I took the fuel line off the carb and cranked the motor over. It pumps a lot of volume, but very little pressure (I can easily stop the flow of fuel with my finger over the line).

Any ideas or opinions before I slap on a new fuel pump and rebuild the carb this week?

 

[berth control]

Also:
I was ruling out any electrical issues because it happened gradually (over a couple miles) , spark loss is usually good or bad, no in between. I was also ruling out timing because it was fine after it cooled down. Also ruling out a dirty or out of adjustment carb. because it happened gradually and then got better after it cooled, a dirty our out of adjustment carb would not get better after the boat sat for an hour or so.

I think....

 

[capecodcruiser]

This is going to be a tough one to diagnose. But I wouldn't rule out a bad ignition coil as well. They are infamous for getting warm and progressively going south.

 

[Boatingnut]

Change the water separation fuel filter first. You can dump it out into a jar to see if there is water in it. A boat we were running with yesterday had the same problem on the way back from Sheboygan. Engine started to lose RPM's. Changed the filter and all was well. There were some nice rollers yesterday, so your fuel was sloshing around.... Start with the easy stuff.

 

[berth control]

Thanks for the suggestions. there were some pretty good rollers yesterday, I'd say 3 to 4's pretty steady where I was.

There isn't a water fuel seperator on my boat, it's a pretty simple and a little crude. The line pulls from the top of the tank and goes directly to the fuel pump via about 6 feet of rubber hose. Then it goes from the pump to the carb. via a steel line. As it enters the carb. there is a little in line filter. I checked it and it was pretty clean. There was some rusty looking debris in there, but very little. Both engines pull from the same tank, but different pickup tubes. I don't think there is a clog there though because the pump put out a lot of volume, just little pressure.

 

[tdappleman]

I had a similar symptom on my old Bronco - turn out to be the ignition coil. It was hot enough after a drive you couldn't touch it - a 20 min drive and it would eventually lose power and then cut off. Certainly easy enough to check since you have twins - just swap them over.

It could be fuel related - but typically if you get water in the gas and up into the carb it's not going to then restart after a bit. If the fuel pump is weak then you could be losing pressure - maybe even having a vapor lock type of problem - but I think I'd start with the coil. It's certainly easy enough to clean out the carb and the float bowl while you're waiting on the part to come in.

 

[berth control]

I had a similar symptom on my old Bronco - turn out to be the ignition coil. It was hot enough after a drive you couldn't touch it - a 20 min drive and it would eventually lose power and then cut off. Certainly easy enough to check since you have twins - just swap them over.

It could be fuel related - but typically if you get water in the gas and up into the carb it's not going to then restart after a bit. If the fuel pump is weak then you could be losing pressure - maybe even having a vapor lock type of problem - but I think I'd start with the coil. It's certainly easy enough to clean out the carb and the float bowl while you're waiting on the part to come in.

Thanks for the advice. I'll check how hot the coil gets next time I try it out, especially in relation to the other engine. The sad, and good part, is that I have TWO spare engines for parts because these engines are known to be so problematic. So far they have shown that to be true.

I am planning on re building one of my spare carbs, getting a new fuel pump, and taking a coil from my spare engine out to the boat. Then test running it until it happens and start ruling things out.

You know that some people say it costs the same to run a boat weather it's new or used, you just chose to pay for repairs or payments. I'm starting to agree.....

 

[stevea661]

Are you sure your water seperator isn't in or on the fuel pump? My old merc 250 inline six had a filter / seperator on the fuel pump.

 

[berth control]

Here's the update:
There is a check valve in the little aluminum fitting at the top of the fuel tank. There is also a screen in there. The screen was dirty, but the check valve is bad. So it was starving the engine of fuel, especially under load. It would be wise for you other classic sea ray owners to pull that fitting out and clean the screen. It is between the pipe and the fitting, so you will have to thread the drop pipe out from the elbow (it will make sense when you are doing it).

Unfortunately, I figured this out after I installed a new fuel pump and rebuilt the carb.

 

[tdappleman]

Good to know - thanks for posting the results back. When I replaced my fuel line I replaced the check valves as well. The interesting thing is my originals nor the replacements had any kind of filter or screen - looked just like a barbed hose connector with a spring loaded ball in the middle. Wonder if I had/have the right ones...

 

[stevea661]

I wasn't able to find a screen on mine either. I did undo the elbow from the tank and tried to remove it and the pickup tube from the tank along with the elbow. whatever is at the end of the pick up tube is bigger than the female threaded tank bung so the pickup tube won't pull out. I did blow through it though and it seemed clear. There is a test for the check valve but I forget what it is. If anyone is interested I can post the specs but my manual is in the boat and I'm in the house in the AC and it's hot out there. Glad you found your problem Eric:thumbsup:.

 

[berth control]

Thanks for the posts guys. My screen is between where the pickup tube and the elbow are, you would never know it's in there if you didn't take them apart, it's a little screen that actually fits in the tube. For what it's worth the marina I bought the new check valves from said to pull the screen out since there are others that do the job and that one clogs easily.