1981 70HP dies in 30 seconds

dr.livingston · Nov 5, 2008

This engine used to run fine. Sat idle for a couple of years. Would not run at all when we tried it a month ago. Rebuilt the three carbs. Now it starts easily and runs strong but dies after 30-45 seconds. Restarts again with no problem. Dies again even from high idle. Seems like it is running out of gas but it starts easily again even without re-pumping the bulb.

At first I thought bad fuel pump or filter. Unfortunately iboats does not carry a rebuild kit for this model year fuel pump - and the online chat helper was unable to locate a source. The fuel filter is clean.

Then I read on another blog about oxygenated gasoline (diluted with alcohol) causing many problems with older engines. What do you guys think?

lyncraft_mechanic · Nov 5, 2008

Re: 1981 70HP dies in 30 seconds

have you tried pumping the bulb to try and prevent the engine from dying? by doing this it will by pass your fuel pump. when you rebuilt your carbs did you level the floats? try this website for your partshttp://www.shop.evinrude.com

Dhadley · Nov 5, 2008

Re: 1981 70HP dies in 30 seconds

How did you clean the carbs? Did you install new OE kits?

dr.livingston · Nov 5, 2008

Re: 1981 70HP dies in 30 seconds

No I didn't try pumping the bulb when the engine was dying, but that's a good idea. I also thought about elevating the fuel tank several feet above the engine so that gravity would help the pump. Haven't tried that yet.

To rebuild the carbs I used kits I bought from iboats. Sierra or Mallory, I don't remember which.

Yes I leveled the floats to specification.

Dhadley · Nov 5, 2008

Re: 1981 70HP dies in 30 seconds

How did you clean the carb bodies?

dr.livingston · Nov 5, 2008

Re: 1981 70HP dies in 30 seconds

To clean the carbs I disassembled everythng and used solvent to loosen the residue. Then, using a spray can of carb cleaner I made sure that all the passages were open. I used a fine wire to probe the passages that were blocked and followed up with more carb cleaner spray until all were clear.

dr.livingston · Nov 6, 2008

Re: 1981 70HP dies in 30 seconds

How about some other ideas?

For example, is it possible that there is a problem with the ignition switch itself cutting off the spark? How would I test for that?

What about the tilt of the motor? The electric tilt and trim on this motor doesn't work and the motor seems permanently stuck in a slightly elevated position. The angle doesn't look extreme but it is not vertical either. Is there any way to manually bypass the electric tilt motor?

boatman48 · Nov 6, 2008

Re: 1981 70HP dies in 30 seconds

i have a problem that's similar to yours that is not solved yet.
search on boatman48 and you can read what i've done so far.

i think mine is electrical problem, maybe your's is also. i plan
to go after the coils and rectifier next.

bowman316 · Nov 6, 2008

Re: 1981 70HP dies in 30 seconds

I had a bit of a fuel delivery problem on my 81 70 hp eninrude. I just made sure that the gas tank was as high as i could get it. Even if the fuel pump is broken, there will be a syphon effect if the tank is higher.
see if the primer bulb is going soft.

does it stall out gradually or right now?

boatman48 · Nov 6, 2008

Re: 1981 70HP dies in 30 seconds

Have you tried squirting pre mix fuel into the carbs when it's
bogging down ? If you do that and the engine picks up then
fuel delivery is a problem.

What would be good to know is if you squirt pre mix and it
makes no difference can you rule out fuel and focus on electrical.

Anyone ?

dr.livingston · Nov 6, 2008

Re: 1981 70HP dies in 30 seconds

The solution turned out to be very simple.

Replaced the spark plugs with the correct type. (Champion QL77JC4) The wrong type had been installed at some point in the past. Also adjusted the idle stop screw to prevent the RPM going too low. Somehow the screw had vibrated (or been adjusted) back to the point where it would not ever contact the actuator arm. I also tested the spark strength on each of the three cylinders using a low cost tester I bought at a local auto parts store. The spark easily jumped a 1/2 inch gap so spark strength was never the problem although having the wrong plugs probably didn't help.

I had also suspected the fuel strainer inside the old gas tank. Another tank I looked at had a mostly varnished-over strainer inside the tank. Bought a new tank and tried both the old and the new one after the above repairs were made. Now, with the engine running properly, it didn't make any difference which tank I used.

boatman48 · Nov 6, 2008

Re: 1981 70HP dies in 30 seconds

Well done !!

Where did you get the spark tester, is there a model # or brand name
you can post. I need to get one.

dr.livingston · Nov 14, 2008

Re: 1981 70HP dies in 30 seconds

I got the spark tester at an ordinary auto parts store - don't remember which one now. It is a simple thing with an adjustment screw to vary the spark gap and a short pigtail wire with alligator clip on one end to ground it. It cost less than 10 bucks as I recall and was probably overpriced at that considering how simple it is.

SKEETR · Nov 14, 2008

Re: 1981 70HP dies in 30 seconds

I looked around at several auto parts stores. Autozone had them.

1981 70HP dies in 30 seconds

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