85' 115HP OMC Sea Drive Surge Issue

[Auxlarry]

I'm new here but have been told that I can get some good answers to questions I have about my engine on this iste.

My 115 has been a great outboard over the years with the third power head having about 150 hours on it.
Just recently I have started experiencing a surging problem while powering up with the engine trimmed all the way in and a heavy load in the boat.

Trim in to pull out of the hole and it starts to run great until it hits about 4K RPM and then it will drop to 2.5K and then surge back up to 4 or 5K and then back down again. I can start trimming the engine up and this issue goes away but it is hard to get the boat up on plain with the engine trimmed up so far.
Once on plane it runs fine unless I trim it all the way in again.

New fuel lines, new spin on filter, etc.

What am I overlooking?

Thanks!

Larry

 

[ezeke]

Re: 85' 115HP OMC Sea Drive Surge Issue

You may want to have your carburetors rebuilt at this time. It sounds as though your float valves may need some work. Be aware that surging is often the result of air leaks in the fuel system.

 

[Auxlarry]

Re: 85' 115HP OMC Sea Drive Surge Issue

ezeke -

I think I can rule out an air leak since I have replaced all fuel lines and even used the recommended clamps. Same issue after changing everything.

The carbs are my next area of attack even though I just rebuilt them when I installed the new powerhead in September.

Got about 9000 hours on this boat over the many, many years of ownership and with the exception of wearing out the powerheads I have never had an issue like this.

Thanks for the suggestions and if I find the cure I will let you know.

Larry

 

[Auxlarry]

Re: 85' 115HP OMC Sea Drive Surge Issue

Ezeke,

OK, I rebuilt both carbs even though they looked great and went through the entire fuel line system from the tank to the carbs, still have the exact same problem.

With a heavy load in the boat (6 people) it gets up on plane and then starts the surging problem. Took the boat out with just me in it and it ran fine, gets up on plane quick and ran at 35mph. Brought it down and back up numerous times and it runs great.

Got any ideas???

Larry

 

[Auxlarry]

Re: 85' 115HP OMC Sea Drive Surge Issue

I'm at a loss!

After doing everything I can think of I still have this same surging problem when the boat is fully loaded and the engine is trimmed all the way in.
He is a list of what has been done.

1. Fuel Tank (under deck) drained and cleaned
2. ALL new fuel lines and fittings from the tank to the engine.
3. New fuel/water seperator.
4. Carburetors rebuilt.
5. New Fuel Pump.
6. Full electrical check

Anybody got any ideas?

 

[ezeke]

Re: 85' 115HP OMC Sea Drive Surge Issue

What is your top RPM at WOT with your average load?

 

[Auxlarry]

Re: 85' 115HP OMC Sea Drive Surge Issue

ezeke,

Runs at 5500 RPM and purrs like a kitten!

As stated before, only does it when the engine is trimmed all the way in when the boat is loaded. Seems like a starving fuel issue but everything is checking out fine.

 

[agefhx]

Re: 85' 115HP OMC Sea Drive Surge Issue

Do you have a plastic fuel line T fitting in that engine? The one that splits from the fuel pump to both carbs. Could be cracked and you would never see it, thats what i replaced on my 1981 115. Replaced it with a brass one, worked good after.

 

[Auxlarry]

Re: 85' 115HP OMC Sea Drive Surge Issue

I do have the plastic tee, OMC part that I replaced last year when I installed the new powerhead.
Have not looked at it that close other to check for leaks. Wouldn't that leak if it was cracked since it is on the pressure side of the pump?
Thanks for the input, I will check it out!

 

[Auxlarry]

Re: 85' 115HP OMC Sea Drive Surge Issue

Still have the same issue!!!!

Took it to a local shop, spent $380 and the mechanic told me it was good to go......NOT!
He told me after checking the timing and the fuel flow that I was starving the engine of fuel when the engine was trimmed all the way in and replaced the fuel line through the Sea Drive mount, I had just done this and it looks like it is routed exactly the same.

Still have the exact same problem (((
With me in the boat it runs great, with 5 people in the boat, same problem.

Get on it from a dead stop, engine trimmed all the way in, and it seems to run good till about 3500rpm and just about up on plane and it falls on it's face, picks back up for a couple of seconds and falls on it's face. Trim the engine up about 1/4 of the way and it runs great, just won"t plane with that much weight in the boat for a half mile......

What have I and the mechanic missed?????