1979/80 Evinrude 4hp - Steady rev drop

edd_barker

Cadet
Joined
Sep 8, 2009
Messages
22
Hi all,

I have recently restored to life my friend's 1979/80 Evinrude 4HP, which he inherited from his Grandfather. It is a European model no: 49B36D, which Dan Gano (who supplied the parts) identified as a 1979 motor (4904/4932/4933) but with the points ignition from 1980/81, the E-4 models. The motor had not run for many years, the following was inspected and serviced before attempting to fire her up:

Flywheel pulled, ignition parts inspected. All looked brand new, even the coils. Points set to .020. HT leads, caps and spark plugs replaced. Spark tested and looked good.

Carburetor stripped, cleaned and rebuilt with carb repair kit. It has a fixed high-speed jet, which I had not encountered before. I tightened this back in to match how it was set before, gently seating, same amount of thread showing.

New fuel lines and OE filter.

Lower unit dropped, new impellor, new drive-shaft seal, and change of gear oil.

After all this and an embarrassing mix-up of the HT leads.....she fired up and ran great in the tank. Adjusted the low speed jet as per manual, gently seat and then back out 1 3/4 turns. It ran happily like this, so I left it. I didn't drop the revs, lean out etc, as I wasn't sure of the procedure for a fixed jet carb, and it seemed happy enough.

Now to the problem, on the maiden sea trial! Again the motor fired up great and propelled two of us happily along in a 60's Mirror dinghy, happy at lower revs. Raising the revs didn't do much apart from produce a lot more smoke, the boat was heavy, too much load for the motor I think so we kept the revs lower. I also noticed that the engine sat quite low in the water, the exhaust holes (6 little ones) were frequently below the water level, but it seemed to be blowing out hot exhaust and a little hot water quite happily. After a short while, 10 minutes or so, we noticed that the revs were audibly starting to drop, slowly. after perhaps another minute or so, the revs had dropped sufficiently to stall the motor. There was no hesitancy, no back-firing, no rough running no mis-firing to suggest running on one cylinder or an electrical problem. After a few pulls of the starter she would eventually fire up again, and then run happily as if nothing had happened! Until the whole procedure occurred again.

I would really appreciate any opinions on the likely cause of this gradual loss of revs/power, and then why it would run happily again shortly after? If it was too rich I wouldn't expect it to fire up again so soon without plugs being cleaned?

Potential causes I have considered:

1. The fuel shut-off switch below the tank was not cleaned or inspected, could this be causing fuel flow problems, or a vacuum? Filter appeared to have fuel in it, although never full. Sometimes wriggling the fuel hose would produce more fuel in the filter.

2. Turning the motor left-right seemed to speed up the rev decline, could this point to fuel flow issue?

3. She might be running hot, the cylinder head was very hot to the touch. There is not a great deal of water flow out the exhaust, although I am led to believe this is normal?

My plan currently is to strip and inspect the fuel cut-off, assuming this is possible and not just a part to replace. I would appreciate the procedure for tuning carbs with a fixed high-speed jet, so I can make sure I am doing it correctly.

Any advice much appreciated!

Thanks,

Edd (London, England) and Hugo (Exeter, Devon, England)
 

Joe Reeves

Supreme Mariner
Joined
Feb 24, 2002
Messages
13,262
I am assuming that there is a plate on that engine identifying it as Model #49B36D. You listed a few other models so that is somewhat confusing. Let me know if I am in error.

4 = Hp.
9 = Year 1979.
B = Manufactured in Belgium.
3 = I forget... Probably length of engine exhaust housing (long/short shaft etc).
6 = I forget... Probably lower unit propeller angle, 90 degree or angled.
D = Factory run code, of no consequence.
********************
(Point Setting Of Magneto Models)
(J. Reeves)

Note that there are other ways to set points such as using a ohm meter or timing light... however, the following will result in a setting so close to being exact that one could not tell the difference.

Make sure that your feeler gauge is absolutely clean so as NOT to transfer oil/grease to the points.

Set the points as follows. Have the flywheel key aligned with the fiber rubbing portion of the ignition points. Adjust the gap so that a .020 gauge will pass thru but a .022 will not. Should there be any question of the points being dirty (touching the contact with your finger would cause them to be dirty), clean them with a small brush and acetone or lacquer thinner.

NOTE 1: Should the operating cam have a small portion on it with the word "SET" imprinted, align this portion with the fiber rubbing portion instead of the flywheel key.

NOTE 2: Should the cam have the word TOP embossed on the top of it, that is a cam that could be installed upside down and this is simply telling you which side is up. It is not a position where one would set the points.
********************
Spark plugs should be Champion J6C plugs gaped at .030 for the points equipped models....... OR..... L77JC4 or QL77JC4 plugs for the solid state ignition models gaped at either .030 (long life) or .040 (strong spark)
********************
(Carburetor Adjustment - Single S/S Adjustable Needle Valve)
(J. Reeves)

Initial setting is: Slow speed = seat gently, then open 1-1/2 turns.

Start engine and set the rpms to where it just stays running. In segments of 1/8 turns, start to turn the S/S needle valve in. Wait a few seconds for the engine to respond. As you turn the valve in, the rpms will increase. Lower the rpms again to where the engine will just stay running.

Eventually you'll hit the point where the engine wants to die out or it will spit back (sounds like a mild backfire). At that point, back out the valve 1/4 turn. Within that 1/4 turn, you'll find the smoothest slow speed setting.

The high speed jet is obviously fixed, should be snugly tight... and absolutely with a clean ID as fuel must flow freely thru that jet before it has access to any other fuel passageway. I have always carefully cleaned those HS jets with a piece of single strand wire as solvent just doesn't do that job properly.

When you have finished the above adjustment, you will have no reason to move them again unless the carburetor fouls/gums up from sitting, in which case you would be required to remove, clean, and rebuild the carburetor anyway.

Make sure that the throttle butterfly just starts to open when the scribe mark on the cam is dead center with the throttle roller or lever... Also make sure that the throttle buttery fly is wide open (horizontal) when at full throttle.
********************
If the fuel tank is part of the engine... check the fuel filter inside of the tank which unscrews with the fitting.

If the fuel tank is separate, with line and fuel primer bulb, make sure it is vented (vent open). When in doubt, loosen the cap.
********************
The small holes on the rear portion of the long exhaust housing serve as an indicator of the water pump operation. The exhaust pressure forces a constant water spray out those holes.

You state that those hole were frequently beneath the water... not good as that results in additional exhaust back pressure. Normally this will not interfere with the engine's operation as many sailboat owners plug those holes with toothpicks etc as that part of the engine (on many sailboats) ends up being inside of the craft. However... they should be left open regardless for proper operation as part of the engine's design.

Height of the engine: The cavitation plate just above the propeller should be approximately 3/4" below the keel... bottom of the boat at the transom... 1" maximum!
********************
If the engine slowed down and actually seized.... that is, you could not crank it over right away and had to wait for it to cool off for a few minutes... that would indicate the engine overheated.

If the engine was able to be cranked over immediately after slowing down to a halt, that would indicate running out of fuel... OR... too much fuel (flooding)... OR... improper carburetor adjustment.
********************
The water pump plate should be sealed to the lower unit..... the impeller housing should be sealed to the plate. Use sealer Bombardier 3M Product #847 which may also be listed as Scotch-grip 847, part number 776964

Let us know what you find.
 
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edd_barker

Cadet
Joined
Sep 8, 2009
Messages
22
Hi Joe,

Thank you very much for your comprehensive reply! To answer some of your questions:

Yes there is a plate on the engine stating Model #49B36D. When I spoke to Dan to order the parts he could not find an equivalent US model number, and so identified the motor from various photos I sent of the motor, carb, LU etc. So the parts manuals I have cover those other models. All the parts I have fitted so far have seemed to be correct!

So far I have failed to:

Ensure that the points were spotlessly clean. I will go back and do so.

Follow the carb tuning advice procedure properly.

Set throttle position.

The fuel tank is integral to the motor. I was not aware of a filter inside the tank, there was only one in the middle of the fuel lines running from tank to carb, which was replaced. I will inspect this, as well as the fuel shut off.

We did not seal the water pump plate or housing either, just refitted. I will go back and do this. Scotch 847 is only available in the UK in 1 litre tins, I assume that a setting gasket sealing compound would do the same job? Hylotyte Red for example?

I will look at the height of the motor and report back. It is an old sail-boat, so may not be correct.

When the engine stalled, it was possible to turn it over on the pull-start straight away, so I do not think it was seizing. The engine would restart in less than a minute.

I will take all of your advice on board, and have another thorough look at the motor before the next sea trial. I will of course report back!

Many thanks again,

Edd
 
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