Is this a Fuel pump issue?

[drexton311]

I had a new issue raise its ugly head today and I am not 100% sure which way to go in trouble shooting it. Forgive the length of the post, do not want to leave anything out…

In the AM I started the boat on muffs and let it warm up. It was a little tough to start, but once it fired up, it restarted several times, no issues noticed, (exhaust seemed black, but I attributed it to being choked in order to warm up). Fast forward about 3 hours and we are on the lake. The boat fires up no problem and I am able to “"high idle”" it in neutral for a few minutes to get it warm and ready to go out - nothing out of the normal there.… So we take off across the lake and it planes out like normal and after a while, especially when we started pulling a tuber, it would fall flat on its face and almost die. Then it would run fine for about 10 minutes and seem like it was just a fluke, then randomly lose RPMs, then a few seconds later, RPMs would rise, then a bit later it would lose RPMs again, then RPMS would rise, then normal for a while, and so on… It appeared completely random mostly passed 2k RPM (unless pulling a tube, then it sometimes was instant), and sometimes would go for a long while with no issues. It just started doing this out of the blue, so I am at a loss for words. The boats idles fine and will rev high in neutral with no stumbles… Is the fuel pump my problem? Besides a pressure test is there a way I can test it? What about the Clear/yellow is hose that runs from the top of the pump to the carb, I had heard that I can test it by seeing if fuel is in it? Any ideas would be appreciated.

Here are the specs:
1988 OMC Chevy 5.0L
2bbl Carb (new this year)
Points ignition
Mechanical fuel pump
New fuel filter about two months ago
Tank completely drained and replaced with fresh gas two months ago (have run fresh non-ethanol gas ever since then)
New plugs, wires, distributor cap
Timing is correct and dwell is correct
Compression is low at 110 PSI (dry test) on all cylinders - I will need to retest as I did not have the throttle in WOT when testing, I assume worn rings, old motor

 

[bruceb58]

Try running without your fuel cap on to make sure the tank venting is ok.

I would then do a pressure test of the fuel pump.

The clear yellow hose will have fuel in it if the fuel pump diaphragm has ruptured.

Your compression is VERY low.

 

[drexton311]

I did notice when I went to fill the boat up before we went out on the lake that the gas pump kept shutting off and would not let me put much gas in the tank (actually I only put about a 1/2 gallon in it), since the boat had been filled up a couple weeks earlier, I just assumed it was still full. would a vent valve blockage cause this by not letting the tank vent when filled? And to add, I did replace the filler hose on the tank when I drained it a couple months ago. Where can I find the anti-siphon valve and how to I replace it or check it? Thanks!

 

[drexton311]

As for the compression, I did not test on a warm motor in WOT, so I am not confident in my numbers, will retest when able.

 

[bruceb58]

The anti siphon valve is the fitting that is screwed into the tank. The fuel hose which goes up to your fuel filter is connected to it.

You can also run your engine on a portable tank to see if it is tank related.

 

[Scott Danforth]

if you could only put 1/2 gallon in your tank, most likely you have a venting problem which would act as you describe.

I also agree, your compression is very low.

 

[drexton311]

Scott can you clarify? "venting problem which would act as you describe."

The vent problem causing the boat not to be filled or the RPM dropping issues or both?

 

[drexton311]

Ok, so I am at a loss for words?
I removed the fuel filter and emptied the contents, no water whatsoever! I checked the carb filter, looks brand new. (Rochester 2bbl 17059860) I then removed the vent hose from the tank and blew in it? no clogs, no issues. It?s a 5/8? hose, so it would take a lot to clog it. I then removed the anti-syphon valve and the thing looks brand new, no crud, no nothing. I then removed the pick-up elbow into the tank and it was only an elbow, so I am wondering if I have a built in pick-up in the tank? (There was no place for a pick-up tube to attach to the elbow.)
So I am stumped?.
Could this be an electrical issue after all? I have an OMC model 502APRGDP. I replaced the plugs several weeks ago, the wires and cap a couple weeks ago. What would a weak coil do?
Please help!!