84 Evinrude 70hp surging

[UNCC Grad]

Motor is surging above 4K rpm. I have cleaned the carbs, tightened all fuel fittings, replaced tank with known good tank, inspected fuel pump screen filter and diaphram and made sure of fresh fuel. Spark test under load shows good spark, compression is even at 100# in all three, choking does not help and the bulb stays firm. I'm at my wits end and am going to look at a 93 model 60hp tomorrow but I want to make sure I'm not overlooking something simple.

I have never adjusted the timing but the advance linkage moves freely with the throttle. I did notice the flywheel had a small amount of play. My only guess now is a worn main bearing and seal causing a vacuum leak.

Any ideas?

 

[noelm]

Re: 84 Evinrude 70hp surging

surging is normaly caused by Fuel supply problems, especially if it is at high speed and a "rythmical" sort of a surge ,when you tried another tank, did it include the hose and primer as well? is there a small in line filter that you have not replaced?

 

[UNCC Grad]

Re: 84 Evinrude 70hp surging

The tank used the same bulb and hose but if those were bad the bulb should go flat, no? I forgot to add that I gapped and replaced the plugs twice.

Looking at the carbs when the surging happens shows a steady spray of fuel throughout the throttle range. There are no inline filters other than the metal fuel pump screen.

 

[UNCC Grad]

Re: 84 Evinrude 70hp surging

Anyone else have an opinion? I'm baffled at this point.

 

[tashasdaddy]

Re: 84 Evinrude 70hp surging

describe the play in the flywheel, side to side, up and down. check for any fuel/air leak.

 

[UNCC Grad]

Re: 84 Evinrude 70hp surging

describe the play in the flywheel, side to side, up and down. check for any fuel/air leak.

Not really any up and down to speak of, just side to side, maybe 1/16" each way...basically just enough to know it's got some play.

Check for fuel/air leak? I sprayed the entire carb lines and fittings as well as the carb gaskets with starting fluid to see if rpms would jump...nothing so everything seems good on the back side of the fuel pump.

One thing I did notice is the line from the fuel pump to the crankcase is turned at a pretty severe angle but it's always been like this, even before the problem started.

 

[F_R]

Re: 84 Evinrude 70hp surging

1/16" play in the flywheel certianly is reason for poor performance. There would be major leak through the seals. Unfortunately, it is not a pretty picture. Consider it toast.

 

[UNCC Grad]

Re: 84 Evinrude 70hp surging

1/16" play in the flywheel certianly is reason for poor performance. There would be major leak through the seals. Unfortunately, it is not a pretty picture. Consider it toast.

I put it up locally for a parts motor. It's a shame b/c it would be a good motor for someone who had the time and inclination to rebuild. Maybe it's a timing issue but I was tired of throwing time and money at it trying to figure it out myself.

I now have a 1993 60hp Evinrude to replace it.