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1993 Evinrude 48-HP High-speed Lean: Eventually Solved

Posted: Sun Jun 16, 2019 11:06 am
by Oldslowandugly
My 1993 Evinrude 48-HP engine was suffering a high speed lean-out condition. At Idle and mid-range [something was] perfect. At full-throttle the carburetors would run low on fuel and the engine would stumble. Squeezing the primer bulb re-filled the bowls, and then [the engine] would run fine again. This was an intermittent problem not happening all the time.

The Evinrude 48-HP engine could run all day at 2000 to 3000-RPM. At 5000-RPM it would run dry.

Some times it ran great all day.

The first thing I checked was the spark plugs; they were clean with no fouling.

I checked all the fuel lines for air leaks. Each 6-gallon tank line has an in-line filter, and both were clean.

I tested the primer bulbs to make sure they were pumping fuel. They easily filled the bowls with fuel.

I made sure the portable tank vents were open.

I changed the Racor fuel-water separator.

I even tried two different fuel pumps.

Nothing helped. Then totally by accident I noticed something wrong while squeezing the primer bulb. I saw the in-line filter element moving back and forth while I squeezed. I immediately took the filter apart and found that the element inside was loose. The knurled ring that held it in place had unscrewed and was allowing the element to move around. Worse, the ring was covering two of the fuel path holes in the fitting. Then when the element moved it covered the other two holes. That is what was blocking the fuel flow, but not all the time.

I tightened the ring and put the filter back together. The engine ran great again. I feel silly not finding this bad filter earlier, but the filter looked fine at first glance and flowed fuel properly for priming. But full-throttle demanded more fuel than it could flow.

Being intermittent I didn't catch on that it only happened with one fuel tank. The other ran fine. As usual- it often is the simplest thing causing big problems.


Re: High speed lean-out NOT solved

Posted: Sun Jun 16, 2019 7:44 pm
by Oldslowandugly
Yesterday I ran up and down the mile long creek leading to the marina six times. At WOT [the Evinrude 48-HP engine accelerated to] 6000-RPM with no problem—not a hiccup.

Today I took out my daughter looking for Bluefish. As soon as [the boat] got on plane the engine stuttered and shook. Same problem—and not solved.

This is getting old.

I may have to pull the boat and rebuild the carburetors just to eliminate them.

Re: High speed lean-out NOT solved

Posted: Mon Jun 17, 2019 8:22 am
by macfam
We had a 2000 40 Johnson 2-stroke on our 13 Super Sport.
Symptoms were nearly identical.

Found a small hole in the diaphragm of fuel pump.

Replaced fuel pump: problem solved.

Re: High speed lean-out NOT solved

Posted: Mon Jun 17, 2019 9:23 am
by Oldslowandugly
I have a fairly new 50-HP fuel pump on there now. I tried another spare 50-HP pump and nothing changed.

Then I tried a 30-HP pump and the engine actually ran somewhat better. At 6000-RPM [the 48-HP engine] only wavered a bit. I attributed that to the smaller volume of the 30-HP pump.

That was when I found the loose filter element. Assuming the pump for a 30-HP was inadequate,I put the original 50-HP pump back on. Then I was able to go up and down the creek with no trouble.

One day later I am back to square one. I even use extended fuel pick-ups with new filters in my tanks. I noticed that when the tanks ran out of fuel there was still almost a gallon of fuel left. The stock pick-up tubes did not go all the way to the bottom. I replaced the pick-up hoses with longer ones that reached the back of the tank. The filters are heavy OMC metal ones that keep the end of the hose down. Now when I run out of fuel the tank is totally empty. The hoses are only a couple of years old.

Today I am going to try switching around tanks and hoses. If there is no change then I know the problem is on the engine. If it is solved then I know one tank and line are suspect.

Re: High speed lean-out NOT solved

Posted: Mon Jun 17, 2019 7:01 pm
by Oldslowandugly
Today I swapped the other fuel tank and line and tested it alone. The 48-HP Evinrude ran at 6000-RPM with no hiccups. But when I stopped, it would not idle below 2000. It would die and not re-start without choking it. Then it would run great until I slowed down where it would conk out again. So I ran back to the dock and shut it down.

Has the time come to rebuild the carburetors?

Re: High speed lean-out NOT solved

Posted: Tue Jun 18, 2019 2:00 pm
by Oldslowandugly
I pulled off the carburetors. Both were clean inside and no crud. All I found was that the float levels were both wrong. I attribute that to worn needle or seats that allowed the needle to go in too deeply. They may have even gotten stuck and failed to flow properly.

I have one carburetor already re-built with a 30-HP kit I had. The other I had to order. The re-build kit for a 30-HP is the same for a 50-HP: same float bowl, float, needle, seat, main jet, mounting gasket.

Re: 1993 Evinrude 48-HP High-speed Lean

Posted: Wed Jun 19, 2019 4:00 pm
by jimh
I am surprised that the high-speed (main) jet is the same for both the 30-HP and 50-HP engines.

Re: 1993 Evinrude 48-HP High-speed Lean

Posted: Wed Jun 19, 2019 4:53 pm
by Oldslowandugly
I didn't mean the same size hole but the same basic interchangeable type part. The 30hp uses a #67 jet in a single carb and the 50hp uses a #55 in two carbs. I mention the 50hp because according to my OMC factory manual that is the carb I have. The 48hp uses a slightly different one but same size main jet. Strange, unless someone upgraded for some reason.

Re: 1993 Evinrude 48-HP High-speed Lean

Posted: Wed Jun 19, 2019 4:57 pm
by jimh
So the main jet is not the same in both 30-HP and 50-HP engines? Is that what you are saying?

Re: 1993 Evinrude 48-HP High-speed Lean

Posted: Wed Jun 19, 2019 5:04 pm
by Oldslowandugly
The threads are the same so they can be interchanged. The orifices are different depending on application. The OMC manual list about a hundred different orifice sizes. I remember that the same type were also used in my 125hp 4 cylinder Evinrude. Pretty smart on OMC's part keeping costs down and allowing fine tuning.

Re: 1993 Evinrude 48-HP High-speed Lean

Posted: Fri Jun 21, 2019 8:18 am
by jimh
So you ARE now saying the jets are different. That makes more sense. The diameter of the opening in the jet is different in different models, based mostly on horsepower rating.

Re: 1993 Evinrude 48-HP High-speed Lean

Posted: Sat Jun 22, 2019 3:21 pm
by Oldslowandugly
This [fiddling with the carburetors is becoming] a pain.

I put back on the two rebuilt carburetors. I adjusted the idle speed per the factory manual. The idle screw settings I recorded before tear-down were much too lean. In fact, I ended up making them a half turn richer than the factory suggested starting point. I now have a beautiful smooth-idling engine.

But at WOT [the engine] still running out of fuel. I ordered a 0 to 3-PSI pressure gauge and some hose barb fittings. I am going to build a gauge manifold to splice into the fuel line. That way I can test the fuel pump output pressure which should be 2.5- PSI @ 4000-RPM.

I am also going to build a vacuum gauge manifold to splice into the gas tank line. That way I can see if the pump is sucking properly or if there is an air leak.

As exasperating as this is, it beats just replacing everything and hoping for a cure.

Re: 1993 Evinrude 48-HP High-speed Lean

Posted: Sat Jun 22, 2019 3:59 pm
by jimh
When you have solved the problem, you will be an expert resource of advice this problem, and you will be able to help others.

Re: 1993 Evinrude 48-HP High-speed Lean

Posted: Sun Jun 23, 2019 8:29 am
by flymo
From your detailed writeup, it's pretty clear that the fuel pump is unable to supply enough fuel. Since you've tried different pumps, the pump itself can't be the concern. Did you replace the pulse line which connects the pump to the crankcase? This could have a leak. Or even without a leak, if the wrong type of hose was installed, or it has just become old and soft, it won't transmit enough of the vacuum pulse to the pump diaphragm to get the job done.

To your point about not wanting just to "replace and hope" it will only cost a few pennies to put a new pulse line on there. Good luck!

Re: 1993 Evinrude 48-HP High-speed Lean

Posted: Sun Jun 23, 2019 8:12 pm
by Oldslowandugly
No pulse line. The fuel pump bolts directly to the crank case. Alternating positive and negative crank case pressure works the diaphragm in the pump. I probably will get a new pump just because, but I want to test the pressure first. If I had a small electric fuel pump I could mount it somewhere outside the motor cover and use that as a test. Unfortunately all my electric pumps are for automobiles and produce too much pressure. Jim said: "you will be able to help others." That is the whole point. I'm throwing this out there in the hope that others can learn. I was this site that educated me about Whalers to begin with.

Re: 1993 Evinrude 48-HP High-speed Lean

Posted: Sun Jun 23, 2019 10:06 pm
by flymo
What seals the backside of the fuel pump to the crankcase? Could there be a vacuum leak there?

Re: 1993 Evinrude 48-HP High-speed Lean

Posted: Mon Jun 24, 2019 7:40 am
by Oldslowandugly
A gasket. Two holes for the screws and one center hole for the pulse. New when other pumps were tested. I'm seeing OEM BRP pumps going for around $100. And of course there are Chinesium pumps on Ebay for s little as $9.50. Even used factory pumps are around $50 these days. Amazing. My hose barb order is tied up in the Post Office right now. Hopefully I can get it delivered today.

Re: 1993 Evinrude 48-HP High-speed Lean

Posted: Mon Jun 24, 2019 7:59 am
by flymo
I'm only familiar with the triples, which use a pulse hose. However, I'm still thinking one possibility is vacuum leak somewhere, preventing the pump from having enough moxie to do the job at high speed. There's just not that much to go wrong with a diaphragm pump, and you've been all over the supply side.

It sounds as though you're running two filters - the Racor and then an in-line. I wonder if the combination is just too much resistance? Maybe try some runs without either of them?

Re: 1993 Evinrude 48-HP High-speed Lean

Posted: Mon Jun 24, 2019 8:28 am
by Don SSDD
With a small on deck fuel tank, I see no need for any filters on the lines. With in deck tanks, yes use a filter but you can check your tanks by sight for dirt and little likelihood of water depending where you buy gas? If from a marina, yes some risk and use a water separator, but not if you buy from a busy auto gas station. Or if you have to use ethanol gas and don’t use it in a month or so, but I can buy ethanol free.

Good advice to try with no filters, it may solve your problem or at least eliminate this as a problem.

Re: 1993 Evinrude 48-HP High-speed Lean

Posted: Mon Jun 24, 2019 4:56 pm
by Oldslowandugly
In a perfect world no filters would be a dream set up. Nothing to leak. Unfortunately the gas here varies from perfect to horrible. I know because of the clear in-line filters. Ocassionaly the crud is so bad I need to take it apart just to run. Then there is the water. I had really never had a problem with water in the fuel until the year before last. I stalled out in the channel. The glass filter was clear- no tint from the gas/oil mix. I knew it was water. So I switched over to the second gas tank, and after using the primer to push the water out, the motor fired up and ran great. I took that bad tank of gas and used it in my car. Then I installed the Racor filter/separator. Not a drop of water since then. So even with the Racor filter before the motor, and a small in-line filter on each tank hose, the motor ran great ever since then. Until now. OK, my hose barbs just came. Now to rig up a testing manifold.

Re: 1993 Evinrude 48-HP High-speed Lean- SOLVED- kinda

Posted: Thu Jun 27, 2019 8:47 am
by Oldslowandugly
I went down to the dock armed with tools, hoses, and parts. I was not leaving until [the problem of fuel delivery at high engine speed] was solved. Even if I had to re-build the whole fuel system.

I changed the line from the engine-mounted fuel fitting to the pump because it was a little soft. No change.

I replaced one of the tank-to-engine fuel lines with a new spare one I had. No change.

I put a vacuum gauge on the engine fitting to test what sort of suction the pump was producing. It showed [4-PSI]. The OMC book wanted less than [5-PSI] so it was within specs.

I put a 0 to 3-PSI pressure gauge on the discharge side of the pump. It showed 3.5-PSI at idle. The book wanted at least 3-PSI, so the pressure was within specs.

At 4500-PRM the gauge showed 2.5-PSI, again within specs. Watching the clear filters I saw no air bubbles from leaks so those were fine.

Then tried to see if the Speed Limiting Overheat Warning or S.L.O.W system was being activated. All the symptoms pointed to that. S.L.O.W. is activated by the temperature switch in the cylinder head. In an overheat condition it cuts the motor speed down to 2500-RPM.

I put an Ohmmeter on the temperature switch, and the circuit showed infinite resistance; the sender was not closed to ground. It may have been activated too soon at some lower temp so I disconnected the wire at the temp sender and tested the boat. No change.

As I sat there taking a break I remembered an old Hot Rodding saying: if on a tune-up, if you change points, plugs, cap, and rotor, then the engine won't work, you go backwards replacing everything you changed until you get to the offending part. Brand new parts can often be bad.

The fuel pump was new and the other pumps did not change anything. The carburetors were re-built and worked better than ever.

Then I remembered that I started the season with new fresh spark plugs as I always do.The day I put the boat in the water the motor ran flawlessly for the five miles to the dock. The very next day the intermittent cutting out began. I scrounged around my tool box and found a couple of old clean spark plugs. I swapped them in. The motor started right up and I went for a test run.

The motor ran right up to 5000-RPM and ran steady. I was floored that brand new plugs failed after a single day of use.

When I got home I cleaned the bad plugs and tested them with an Ohmmeter. One tested about 150-Ohms, which is what other good plugs tested at. One showed infinite resistance. That meant there was a physical break inside the plug forcing the spark to jump it.

So was the problem caused by the spark having to jump two gaps?

Or did jumping the break produce so much Radio Frequency Interference that it triggered the S.L.O.W. system?

The service manual warns about routing the engine harness too close to the spark plug wires just for that reason. Being that the motor was forced to run at 2500-RPM or less, I tend to believe the RFI was the culprit.

At any rate the problem is solved. The only money I spent was for a $16 carburetor rebuild kit which was due anyway. Lots of wasted time and aggravation though.

Now to go fishing.

Re: 1993 Evinrude 48-HP High-speed Lean: Eventually Solved

Posted: Thu Jun 27, 2019 9:33 am
by jimh
From the long narratives of repairs, you seem to have solved the original fuel delivery problem, but then created a deceivingly similar symptom by installation of a defective spark plug.

Good work to persevere and find the solution.

Re: 1993 Evinrude 48-HP High-speed Lean: Eventually Solved

Posted: Thu Jun 27, 2019 9:40 am
by Oldslowandugly
Thanks Jim. Although I discovered numerous small problems with the fuel system, I have to believe that the entire episode was caused by the defective spark plug. Every year I am tempted to re-use the spark plugs if they look good. But I change them out just because. Looks like this year I got stung.

Re: 1993 Evinrude 48-HP High-speed Lean: Eventually Solved

Posted: Sun Jun 30, 2019 4:10 pm
OS&U: Congratulations. There is hardly a better feeling than when the old outboard is running well again. So I must tell you my story, and it has to do with your observation that new parts sometime are not functional like we assume they are.

My son's 1977 Evinrude 140 (V4) is a very good engine. However, it started running rough at idle and would not make full power. Fuel as the cause was eliminated quickly.

First, change spark plugs, easy to do, relatively cheap: no joy.

I tried to isolate the cylinder causing the problem, but the problem was intermittent. Running the engine with one plug disconnected at a time did not show anything obvious.

Since the ignition coils looked like they were original, they were the next to be changed: no joy.

We went thru the entire ignition system looking at charge coils, wires, trigger coils, etc., but absolutely no joy.

We even changed the Power Pack (electronic ignition).

In desperation—just like you—I went backwards. We put on one of the old coils on successive cylinders. On the third cylinder we tried: VROOM! Lots of joy.
Like your new plug, our new ignition coil was faulty. Wow was I mad. Had the new coils all been good, we would have been done quickly.

The point to be taken is that there are risks to assuming that troubleshooting and repair by part replacement works all the time.


Re: 1993 Evinrude 48-HP High-speed Lean: Eventually Solved

Posted: Tue Jul 02, 2019 6:56 pm
by Oldslowandugly
I feel for you Al. Same as me- stung by a "new" part. But at least you found [the defective new part] and are on the water again. I've seen guys lose an entire season over a dumb problem.