Surging Engine at High RPM's.

[longisldr]

I have a 1985 Mercruiser 3.0L, 181cid, 140hp stern drive engine. It just went through a complete rebuild. The first few trips ( almost 90 miles) were uneventful. Today, I went out with the family and 15 minutes into the trip, cruising at approximately 27mph and 3500 rpms, it started surging badly, I lowered the rpm's to approximately 1500 and it evened out but no longer on plane. Every time I tried to plane the boat, it would bog down. I also noticed when I finally got it to 20 mph or so, every bump or wake I hit would make the engine surge again. I am sure the fuel filters are good because they are brand new and I checked them before I left. I did notice some slight dry rot on the rubber diaphram inside the fuel pump from sitting for a season. The carb is rebuilt but is still a suspect. I am leaning toward fuel pump and/or carb. Any input would be greatly appreciated.

 

[Limited-Time]

Re: Surging Engine at High RPM's.

I have a 1985 Mercruiser 3.0L, 181cid, 140hp stern drive engine. It just went through a complete rebuild. The first few trips ( almost 90 miles) were uneventful. Today, I went out with the family and 15 minutes into the trip, cruising at approximately 27mph and 3500 rpms, it started surging badly, I lowered the rpm's to approximately 1500 and it evened out but no longer on plane. Every time I tried to plane the boat, it would bog down. I also noticed when I finally got it to 20 mph or so, every bump or wake I hit would make the engine surge again. I am sure the fuel filters are good because they are brand new and I checked them before I left. I did notice some slight dry rot on the rubber diaphram inside the fuel pump from sitting for a season. The carb is rebuilt but is still a suspect. I am leaning toward fuel pump and/or carb. Any input would be greatly appreciated.

Sounds like water in the fuel, re-check you filters to make sure you did not get a load of bad gas.

 

[mtroy]

Re: Surging Engine at High RPM's.

I agree with water in the gas. It stays at the bottom of the carb bowl. When you hit a bump it mixes with the gas and get sucked up into the main jet.

 

[Windykid]

Re: Surging Engine at High RPM's.

Agree on water in fuel.

 

[longisldr]

Re: Surging Engine at High RPM's.

Here is a little tidbit I failed to mention. This surging actually started on my last trip out before this recent episode. My gas gauge showed a 1/2 tank but it really only had 3 gallons left in it. I found that out when I filled it up and it took 23 gallons and I have a 26 gallon tank. I immediately checked my filters thinking I got residue from the bottom of the tank in them and they were clean. Thinking that maybe I was just low on fuel which was causing the surging, I filled it up and went out and it was fine until it started again. I did fill up from a different gas station so I would call it a stretch to say that two reputable gas stations had water in their gas. If it is water, will adding a seperator correct the problem? My boat does not have one and this may be my "wake up call"!