engine dies: 1989 70 H.P. Evinrude runs for five minutes, then quits

Dont waste your money on a Compression tester,---- its not that.

As with any book the writer is assuming you know basics.

A manual is written for someone that knows engines but not that particular one.

 

The manual he has does have the basic methodology and mechanical procedures in the first few sections. I'd agree about the compression tester, though knowing if the cylinders are all about the same, isn't a bad idea as part of the general evaluation.

Simply put, there are many consumable items on the engine that wear out or become less than reliable. They are changed out as required, but given this engines history, the wise thing is to just hank it all off and replace it. Yep, it'll cost more than the "hunt and peck" method possably, but you'll gain several things by doing this. First is you'll have a "level playing field", by which to make reasonable tests and assessments. Second, you'll know the life of the consumables, so a reasonable routine can be established. You will also become familiar with the components and the general state of things. Lastly, during the parts R&R and subsequent tune up and evaluation, you'll very likely find the fault or faults, causing the current set of issues.

If it was my engine, I'd replace all of the usual ignition system components, like cap rotor, wires, plugs, etc. I'd check the advance weights and set the timing too. I'd change every filter, just to start with a clean slate and likely would also replace old rubber fuel lines with ethanol compatible stock too. I'd check, if not replace the coolant hoses and all clamps. I'd check each electrical connection on the engine. I'd also fully service the fuel delivery and metering system. Then the engine would be set to factory spec's and some basic tests preformed. In all likelihood, in the process of this afternoon of work, you'd stumble upon the cause of your ills and you boat will be up and running fine again, but now with fresh parts, who's reliability can be trusted.

This is just the common sense way to approach any new car, motorcycle, boat, what ever. Personally, I don't have faith in a new project, until I know what the "tune" is and more importantly, that it's not going to force me to paddle home, because I know the parts are new and the engine to spec.

 

I would think the first plan of attack would be to unclip the fuel connector off the motor, depress the ball valve, squeeze on the primer bulb to ensure all is clear, and fuel is being delivered. If that is good, move on to the engine itself.

 

Good!
Because you wrote there was some fuel coming from the plug on the tank while you pressed the bulb, the non-return valve in the bulb doesn't seem to close.
It could be faulty, but the most logical explanation is that you are pumping air instead of fuel because the connector on the tank has a damaged seal.
There is a tiny O-ring in it that prevents air getting in (and fuel getting out).

 

I agree, there would be things I (and the rest of us, with some experience) would check first with these symptoms, but I look at this like buying a used car. Nothing is known, the age or previous replacement of any of the parts, so inspection, some tests and R&R of the usual tuneup parts would be the reasonable first step, assuming you knew little about the systems and operation of these engines, which appears the case here. It's relatively easy for us to pin down an area to explore, but the original poster seems at a lose. I too think it's probable the fuel connector is bad or has something in it, preventing a good seal, but without going over it myself. He's changed the fuel lines and tank, so this is the logical place to look first, as this is what has changed most recently, though what portion of the lines were replaced: just the hoses or new connectors too? Vent lines? Just too many variables to pin down anything. I'm sure any one of us could nail it down in a few minutes and some simple tests, but I still think he might be better served, with the systems familiarization of a tuneup and basic diagnoses procedures, which are outlined in the book.

 

Plugs

Does your engine overheat,or has it ever overheated?
Spark plugs that have been overheated will break down under load.Some types of plugs are more vulnerable than others.
Restrictions in the exhaust flow will hike up the backpressure,and act like an exhaust brake,especially on a two stroke.This will cause a loss of power,overheating and possibly a piston melt down.
If the engine runs at full revs for a while it means you are getting fuel,if it's difficult to start after it has conked out,I would look at the exhaust flow,and change the plugs.If there is a problem with a partially melted piston,then a compression test will reveal it.check your crankcase seal and head gasket,the crankcase is a mixing chamber,a leak here alters your mixture tune and weakens the mixture resulting in overheating.
The exhaust flow on a two stroke is crucial to its power output,thats why motocross bikes have an expansion chamber in the system,without it their power output is a lot less.

 

I had to remove the powerhead and replace the lower crank seal on an old 70 3-banger Johnson that I had, although that problem affected the idle more than anything and only created a sruging at moderate and higher throttle settings.

Sounds to me like a change of fuel fittings and the fuel ball would be a good start; its gotten to the point where I have to change those items out on my OBs about every two of three years

 

Spark plugs can fail but they don't start right up again, neither do coils and leads . I doubt if it has a distributor.

Its fuel all day long until the cows come home.

Compression will not do this, at high RPM it happens so fast you could run without rings --if you could get it started.

 

o rings

I certainly was not aware that the fittings contained small o ring as you described, will definitely check that.

Is it the connector on the fuel tank or the connector on the fuel lines that have the o rings?

 

No over heating

No, the engine doesn't overheat, it gets warms when running, but I never run very fast anyway.

 

I'll be very interested to know what the cause of your problem is,when you have sorted it out.Hope you will post on here and let us know.

 

Yes, rest assuredly, I will post the fix and I certainly appreciate all the ideas you nice individuals have posted for me.

 

If the bulb and lines have been on there 'forever' and you can't pump the bulb up solid....I'd replace the bulb and lines first. But since you see gas leaking out where the line attaches to the tank, that would be a swell place to be sucking air into the line. So I'd get a new bulb, tighten all the connections and then get a manual too.

 

You are more than welcome,I personally find this site and its members very helpful.The fact that it has a worldwide membership to communicate with is fantastic.

 

I have been to UK many times while working with Joy Global, Inc and made lot's of friends there and learned to eat blood pudding, yum.