3.0 engine stalling out after 20 minutes.

[offshore79]

I have yet another gremlin in the machine.
1989 OMC (GM) 3.0L 20 ft Baja bowrider.
I bought the boat at an auction in the spring and have been trying to get it right ever sense.
Rebuilt engine (thats a long story that took 1-1/2 months), rebuilt carb, new points, condenser, coil, plugs, wires, used but good head, new impeller and housing. Everything else was cleaned and/or tested and reinstalled.

Now that I have done all this and I get it running great, it stalls out on me.

I run the engine to about 4000rpm to get on plane and immediately pull back to 3000-3500 rpm. I keep it there at a steady 25mph and it doesnt sound like the engine is overworking at all (how nice to be back on the water after 10 years) then after 20 minutes, blaaa it cuts out to about 1000 rpm or so, and then back to speed for about 2 seconds, blaaa again, so I drop the throttle down to about 800 or so rpm and it runs great again.
After about 5 miniutes of puttering around I tried it again and this time I was able to get on plane for about 5 minutes and then, yup, blaaa, so I took it back home and prepared to read alot of iboat post's.
It seems like the suggestion for similar issues is to look at the fuel system so I looked and I made a very small adjustment to the float in the rochester 2bbl and back out to the lake.
Exactly, and I mean exactly the same thing.
Seems like good fuel pressure and it's a brand spanky new filter.
What am I missing on this?

Thanks
Offshore 79

 

[Rocky_Road]

Re: 3.0 engine stalling out after 20 minutes.

Make sure that the vent for your gas tank is clear. If not...the longer you run, the more vaccum you create in your tank to the point of fuel starvation. Easy check is to loosen (crack) the gas cap to allow air to enter, and see if you can remain on plane without any issues.

Happy boating!

 

[Bridar]

Re: 3.0 engine stalling out after 20 minutes.

Are you running with a 10 micron fuel filter or a 30 micron filter? A 10 micron filter does a better job at catching moisture, but can sometimes be too restrictive under WOT.

 

[offshore79]

Re: 3.0 engine stalling out after 20 minutes.

Thanks guy's,

Well, I'm going to run a few test's.
I have some pretty long plug wires so I'll shorten those up in the event there is something going on there.
I'm going to recheck or reset the timing, just to be sure.
I'll pull the fuel filter to check if it's still in new condition and see if the micron size is on it anywhere.
I'll then take it out to the water and when (if what Ive done didnt fix it) it starts to fall off in RPM I'll check the coil to see if it's unusually hot. If not, I'll crack the gas cap and see if there is a vacuum.

With any luck I'll get this figured out before the first snowstorm.

 

[offshore79]

Re: 3.0 engine stalling out after 20 minutes.

update:
I shortened the plug wire's (the right thing to do).
I pulled the vent tube from the tank and that was free and clear as I thought. I pulled the fuel line and removed the check valve as well as checked the check valve for proper function and all seemed well.
I checked down into the tank and that as clean as can be.
I pulled the fuel filter and it looked clean but I didnt find anything to tell me what the micron size was but while I was there I noticed that the fuel filter gasket had two breaks between the inner and the outer rings. Well I dont have another gasket around so for the purpose of testing I removed the inner ring. This should be OK as the filter seats on the metal taper of the lower pump.
Back out to the water.
There was between 2-3 ft chop with the onshore wind so to keep a 20ft boat at 30ish miles per hour was a bit of a ride.
I started watching the clock at 2:30p and expected that at about 2:50 the engine would start to drop in RPM.
I ran for awhile in and around 3500 rpm, checked the clock and 2:45, wait, any minute now, 2:50, 2:54......Hmmmmm. So I kept going....3:00, Hmmm, 3:10......Hmmmmm and finally 3:15and still at around 3500.
I killed the gremlin. The broken filter gasket (inner ring)must have been getting sucked into the fuel passage and not letting enough fuel get to the float bowl.
There have been just a ton of these little things with my auction purchase and a whole summer of work. Just in time to winterize it.

I'm finally going to move on to the interior.