1975 35 HP Evinrude Runs Great for a While Then Sputters/Backfires and Dies

I have a 1975 35 HP Evinrude that would start fairly easy run for a short time then start sputtering and acts like a backfire and dies. I went through the carb and cleaned it again and then went through fuel pump for the first time and one of the two springs that was embedded in the plastic casing was sideways so I reset that and carefully put it back together with the OMC diagram so those two parts are good to go.

I got it going again and ran very well for several minutes (much longer and better than before carb and fuel pump cleaning) then sputters/backfires and dies. Starts back up only for a very short time and dies. It did that a couple times and now won't start at all.

Good even compression around 120-125 top and bottom. Pumps tons of water and stays cool. Tested spark after having issues and seemed spark was intermittent but could have been bad connection on tester but pretty sure it is strong (at least a 1/4" gap, didn't measure exactly could have been more). Top plug was darker and both were wet and they were new plugs. Cleaned them up and still won't start. Primer bulb was staying fairly firm and even tried pumping when starting to die and didn't matter.

I believe it is an electrical issue and possibly bad or dirty points so I pulled the flywheel. The points looked nearly new but were a little tight with the tolerances so I reset them and cleaned with a business card and sure enough they were dirty. There was a small amount of what appeared to be fuel around the points and other areas nearby.

My question is, is the sputtering/backfiring/kickback caused by dirty points or does it sound like I have a coil heating up and going out when it warms up or...? I should probably replace the top seal regardless since it appears it is letting fuel passed it. Any other ideas? This thing ran like a top for at least 3-5 minutes then started having issues.

Thank you.

If the engine will start and run now as it did previously explained.... does pumping the fuel primer bulb (acting as a manual fuel pump) make any difference.

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(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.

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Fix the obvious first yes you must address the upper crank seal. They did not make a 35hp in 1975 that I could find what is the model number of the engine.

Joe, I did try to pump the bulb and it still died. I did reset the points as you have described and will clean them as well.

It is a 25 HP and not 35, I tried to edit my post but does not allow me to, sorry for the typo. I have a crank case seal on order.

I hope to get it back together soon and will post my findings.

IMO with the external coils you should set the points exactly .022 or use a timing light. The timing light takes more time but the engine will idle much smoother. Ignition timing is on point gap there is two marks on the outer edge of the points plate and two lines under the flywheel 180 degrees out. shine the timing light at the two marks on the plate and the single mark on the flywheel needs to be in between the two marks. Then you can torque the flywheel nut to spec and see how she runs.

I got the top seal replaced and tried starting it today but will only start with the throttle about half way open or maybe a little more. Revs high then dies. Will start consistently at high throttle but is too high. I was very careful with setting the points and even cleaned them with acetone. What position should the throttle be at when setting them or does it matter? I did at wide open throttle, could that be causing my issue of only starting at high rpms?

When trying to start at normal position it would only pop and backfire a little and release some smoke so I know spark is happening. Just seems to be off a little. Carb is cleaned, linked and synced.

code1p36,you mentioned you pulled the flywheel, Was it installed properly and torqued to specs.

Yes, I made sure the cam key was lined up and torqued to specs.

Are the spark plugs wet? If not put a little fuel mix directly in the spark plug holes and give it a whirl. If she fires up it is a fuel issue if not it is a spark issue.

Have you checked for water in the tank? Drain the float bowl in a small dish and see if water comes out?

The next step was going to be squirting a little fuel in the plugs but it must be getting fuel since it pops and back fires when trying to start at the normal starting spot. The fuel is good because I just tried the same tank on another outboard and it ran like a top.

What position should the throttle be when setting points?

Put a timing light on it and shine the light at the two marks on the side of the points plate. The single mark on the flywheel should be inbetween the two marks on the plate for both plug wires. Adjust the points so that happens and it should run just fine.

The problem is that I can't keep it running to use a timing light. Never used a timing light with an outboard before so I am assuming it needs to be started to use the timing light?

No if you have good spark you can watch the timing marks and see if they line up just pull the plugs and set them on a good ground plugged in on the wires. Have someone turn the key as you check the timing.

There are two marks on the flywheel 180 degrees out one for each cylinder.

Ok, gotcha. It is a pull start but I should be able to have someone pull it over or put a drill on the flywheel nut while I check timing.