84 SeaRay Seville has hard time after 30 minutes

[HRHVT]

Hi,,
I am having a problem with my 1984 sea ray Seville, mercruiser 3.0l .
It had some problems last year with taking off when I punched it, as in pulling up a skier, it would stall for a second before taking off.
So, the local, well known mechanic said it was a certain part in the carb ( I forget what it was called, but anyway) he replaced it and it doesn't have that problem anymore.

However, what it does do now, is after warming up, going fast for maybe 20 or 30 minutes, it drops rpm's all of a sudden (sort of) and then starts sputtering out and dying. It can usually be restarted, or if I catch it soon enough, and back off the throttle it will go along in low rpm's.
If you try to speed up much at all it will die again.

I changed the plugs, emptied the old stale gas and filled with premium non ethanol, also added some seafoam, cleaned the points, and changed the fuel filter.
Problem still exists. Today I went out with an extra tank filled with Premium non-ethanol gas and it did the same thing. So that would preclude stale gas, vapor lock, etc.

I am going to change the ignition coil this week, because I have read a lot about that perhaps heating up and not working.

Otherwise, just looking for some advice, or at least diagnostics to go thru before taking it back to the mechanic to see if carbs are just adjusted wrong.
I have no idea how to set them.

Thanks ahead of time

 

[alldodge]

If your well know respected mechanic didn't do any testing, he just guessed. Replacing the carb is easy to do but not always the problem. What you need to do is see how your fuel pump is doing by checking the pressure, it should read 4 to 7 psi.

 

[thumpar]

A carb rebuild kit is a lot cheaper than a new carb but it doesn't sound like the problem or at least not the dieing after a certain amount of time. Try keeping the fuel filler cap loose and running it. It could be a bad vent.

 

[HRHVT]

Thanks for the tips. The mechanic changed some other part within the carb that was making it not accelerate as quickly as it should, always bogged down for a sec. I forget what the part was called, but he didn't change the whole carb.
That was a separate problem form this, although this new problem did start happening soon after, thats why i mentioned it.
As far as the vent goes, I think I am ok, because yesterday I took the boat out with an external gas tank and I had the filler hose just shoved down into it. No lid on the tank, so plenty of venting.
Could it be electrical? Perhaps ignition coil gets hot after a while, or maybe carbs are simply not adjusted right? although it does run fine for 20-30 minutes at a fairly fast speed, then it is just all of a sudden that it needs to limp home.
Seems as if I went back out today it would do the same thing, so maybe something to do with getting warm??
Thanks,
Kevin

 

[alldodge]

Post 2

What you need to do is see how your fuel pump is doing by checking the pressure, it should read 4 to 7 psi.

 

[Scott Danforth]

Your mechanic probably changed the accelerator pump. Dying after 30 minutes sounds like a blocked fuel vent. Back off the fuel fill cap and put a piece of duct tape over it to keep from looking it. If it doesn't die, the the issue will most likely be a plugged fuel vent.

Other possibilities are a bad anti siphon valve,or a plugged fuel filter

 

[HRHVT]

I think it was the accelerator pump that was changed, and that did fix the original problem. No more hesitation when "taking off".
How do I test the fuel pump? It is a mechanical pump and I have no idea what tool i need to use. I guess there is something that I would hook up to the "outlet" hose? Would the boat just have to be turning over, not actually running when I do this? Also, would I need to check it when first cranking it up and everything is fine, or wait for it to "bog" down again and then test it?
Thanks for that help.

2nd question is in regard to the blocked fuel vent. I did run the gas line into an auxiallary tank with o cap on it, so would that not preclude any sort of blocked vent? or is there something I am missing.
The fuel filter was changed out right after i started having this problem,
I am perplexed..
Thanks again

 

[alldodge]

Need a vacuum fuel pump tester and Tee it inline between the carb and the fuel pump. Remove the fuel line into the carb, install a fitting into the carb which will accept rubber fuel line. Attach the gauge, fuel pump line and carb line to the Tee with hose and hose clamps.

Most auto parts stores have all you will need
http://www.harborfreight.com/fuel-pump-and-vacuum-tester-93547.html

 

[HRHVT]

Ok, Think I got it. I will swing by the parts store tomorrow and pick one up. Would it make a difference if i test it after just starting it, or do i need to wait till it "breaks down" and then see if it is different? Would the pump go out after 20-30 minutes of higher rpm's on the lake, and then not be good again until engine cooled back down?

 

[alldodge]

Doesn't matter if hot or cold, before of after. It needs to be connected and taken for a run. What I'm thinking is happening, is the fuel pump is not keeping up do to a restriction of its weak. So if your running hard or easy the pump should be putting out 4-7 psi. So take it for a run and see if the pressure starts dropping or bouncing

 

[thumpar]

If you have an extra hand you could have them watch the gauge when the problem happens.

 

[HRHVT]

Sounds good, I was thinking more of carb out of adjustment. Especially since I have been fiddling with the screws, or perhaps an ignition coil, because of what else I read on this forum.
But I will test the fuel pump to see if that is a simple fix. Sure hope so.
Thanks,

 

[HRHVT]

ok, well, I wasn't sure about the fuel pump. May or may not have tested it the right way, so to be sure, went ahead and changed it out anyway with a new one.
Also, changed the fuel filter again.
Went out today, and still used an extra gas can I had, took the top off and fed the fuel pick up line right into it. Ran around the lake at around 3-3.5k rpm's, and it still did exactly the same thing.
Lasted for about a gallon and a half, which was right around 30 minutes. and then would only run at a little past an idle.
Oh, Still using premium, non ethanol gas.
Very frustrating. What should I check or replace next?

Thanks again for any and all help.

 

[alldodge]

It's my thinking that your "still" running out of fuel.
Which fuel pump do you have, one on the left or right?
Also what part number was on your new fuel pump?

 

[HRHVT]

I have the one on the left, the old design, and the new one that i have now is sierra part # 18-7278

 

[HRHVT]

Would it perhaps have these symptoms if the fuel line itself had some gunk in it?

 

[HRHVT]

Or is there a way to adjust the carb or to make sure it is working right?

 

[alldodge]

Messing with the idle mixer screws will do nothing to help, they are just for idle. Your running out of gas so the fuel lines could be clogging, but the rubber fuel line could be collapsing. The puzzle is the 30 minute run using a gas can. So if you still have the metal line going from the pump to carb, the only thing left is the fuel line.

When the fuel line was stuck in the gas can it was the bare rubber fuel line, it didn't have a fitting on the end of the hose, correct?

 

[HRHVT]

yes, that is correct, i just disconnected it from the fuel tank, and placed it inside a gallon jug of gas. When that got low i switched it to a second gallon jug of fresh fuel.
Two different weekends now the same thing happened at the same time. 1 1.2 gallons into cruising at about 3k rpm's. Same thing as used to happen all of last summer with the line going right into the fuel tank.
I pulled the line off and put into the fresh fuel to make sure i wasn't suffering from stale gas or anything like that.
I used to run regular gas with ethanol treatment.
So I could go ahead and change the rubber hose, quick, easy, inexpensive fix.
Anything else I should change before trying it on the lake again?
It is frustrating to change 1 thing, go to the lake and have it not work. More frustrating is that I then have to wait another week to test a 2nd thing.
Thanks for your help,

 

[HRHVT]

If I o out again next weekend, and it happens again, should i spray some starter fluid or something like that into the carb to see if it picks right up?