Engine dies after 70 minutes. With gasping

D-po

Cadet
Joined
Aug 14, 2020
Messages
9
-NOOB WARNING-

Hi, I’ve never posted before but I’ve read and read thru the forums and can’t find my specific issue. I’m sure it’s been answered but I can’t find it.

-NOOB WARNING-




MY BOAT:

1976 Mark Twain Tri-hull open bow.




My Motor:

Mercruiser 120HP 2.5L 4CYL




MY SITUATION:

It starts on the first crank and idles beautifully. After it warms up it starts to rough Idle. This is accompanied by what sounds like a gasping noise coming from the top of my fuel tank(it’s tight so I can’t see up in there to see what’s making the noise)

It sounds kinda like Pshh....Pshh....Pshhh... and sometimes it gets quicker and shorter Psh..Psh..Psh..

and then after a few minutes Of rough idleing ...it dies.

It gasps even if the fuel cap is off.

I even sprayed starter fluid directly into the carb but still won’t fire up. I let it sit for a day or two and it fires right back up and runs fine until it warms up for about an hour or so.




WHAT IV’E DONE SO FAR:

Now she didn’t always run this well. I bought it as a non running project.

When it fired right up I thought I lucked out.

So I Changed the impeller and drive coupler new rear motor mount gear alignment etc etc etc etc... and I took it to the lake.(my first time)

I pulled it off the trailer and left it to idle at the dock while I parked the truck. Like I said it was my first time so doing that all took around 15-20 minutes. I Stepped aboard and noticed the rough idle and then it died.

I got it to start again after about 30 minutes but it just rough idled some more and died. Would not restart. (THANK GOD WE WERE STILL DOCKED!)

I Brought it home and let it sit for a couple of days and it started up fine on the hose for about 20 minutes and then died.

After checking the forums I changed the plugs, wires and coil. Now it runs for 70 minutes and dies. Which makes me think I’m on the right track but the gasping sound makes me wonder if I’m going down the wrong rabbit hole? I Also tried removing fuel fill cap but it still gasps.

And as I mentioned I also sprayed some starter fluid directly into the carb during the issue with no change.




Also, it’s cooling perfectly right around 138 degrees. Compression is 125 using just the battery to crank with plugs out and with the throttle wide open. Can’t find the choke.(automatic?)

I know it’s not great but it’s not dead either all cylinders are within a pound or so of 125psi.




Now I’m not a mechanic my boat just wants me to be one and I can’t seem to stop myself from fixing it. So far it’s been like a cruel one way relationship and while Im happy to announce that I did get to spend the whole summer on my boat I have to admit that only 30 minutes of that was in the water, the rest has been in my driveway. Still hoping to just get one ride out of it before I pack it up for the winter. Any help is much appreciated!!!




THANKS!
 

gm280

Supreme Mariner
Joined
Jun 26, 2011
Messages
14,605
I have to say it sounds like your gas tank breather is plugged to me. It runs and sucks all the gas it can and the gasping sound is air trying to get into the tank.

I couldn't watch the video because it was trying to upload a video and to check back some time later. But you have to allow the gas tank vent to allow air in as you suck the gas out. Otherwise it creates a vacuum and the engine will die from lack of fuel... But that is just my uneducated idea not seeing your video or anything else... JMHO
 

D-po

Cadet
Joined
Aug 14, 2020
Messages
9
Gm280.

Thank you for responding! That does sound feasible but wouldn’t removing my gas cap bypass that? Also wouldn’t spraying starter fluid directly into the carb bypass that as well?

I will try to find a better way to get that video uploaded. Apparently IPhone is not its favorite device to upload from.

Thanks!
 

moonrakercat

Cadet
Joined
May 11, 2012
Messages
26
If you remove the gas cap - that should fix any negative fuel pressure problem.

The fact that it runs for a while then stops - it might be heat related.

I suggest that next time it does this & dies - first turn it over and check to see if you have spark.

If you have spark - then check the carb to see if you have fuel in it - pumping it while looking down the holes on the carb you should see some fuel shooting out - if you don't - you may have a plugged fuel filter. Sometimes there is an external filter as well as one right on the steel hose fitting that goes into the carb.

Rather than starting fluid - try dumping a very small amount of gas down the carb - if it fires you have a fuel problem - if it doesn't then prob a spark problem.

I tried to look at your video - but it does not work.
 

D-po

Cadet
Joined
Aug 14, 2020
Messages
9
Moonrakercat-

Thanks for responding. I am working on that video and hopefully will get it posted later today when I can get to a regular PC.

I’m starting to wonder if I have a dual issue. Maybe plugged vent/ electrical? Maybe I will change the Rotor, points and condenser while I’m messing around with it.
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
38,955
check the anti-syphon valve if equipped with that item.----check fuel line including the pick-up tube INSIDE the tank.
 

D-po

Cadet
Joined
Aug 14, 2020
Messages
9
Here is the boat running. Big metal gas tank on the port side next to the motor.
 

D-po

Cadet
Joined
Aug 14, 2020
Messages
9
BOAT RUNNING.

Well I did warn you that I'm a noob. the last links try to force anyone that opens them to sign up for an account so i made some new ones with youtube. try these they will work better!...I think...
 
Top