1980 Johnson 70. Perfect idle, dies at speed?

[SpamPutney]

I have a 1980 Johnson 70hp. Runs perfect in driveway at all speeds. Idles great in the water. AS soon as throttle is opened up, ups and dies. Can adjust choke to keep engine running at WOT, but won't idle at that setting. Also, WOT only gives about half the speed it should. Cleaned and rebuilt carbs, no change. Had a professional clean and rebuid carbs, still no change. Compression is perfect. Any ideas? Thanks

 

[JB]

Re: 1980 Johnson 70. Perfect idle, dies at speed?

Hi, Spam.<br /><br />All multicylinder outboards that are running on less than all cylinders are very convincing actors at idle and with no load. How they "seem" to be running at idle and without load is meaningless.<br /><br />My guess is that you are making power with only one or two cylinders. Check idling behavior with one spark plug disabled. If disabling a cylinder does not drop rpm, that cylinder is not making power.<br /><br />Behavior with partial choke suggests that you have a fuel supply problem or a scavenging problem. Test your fuel pump. Inspect the reeds and the bypass covers for leaks.<br /><br />Let us know what you find. Good luck.

 

[sadam68]

Re: 1980 Johnson 70. Perfect idle, dies at speed?

just for laughs, check all your connections to your coils. i just had a very similar problem and also thought it was a fuel problem but i noticed thet my coil wires had all vibrated loose. i tightened all and the motor runs fantastic!

 

[petkr]

Re: 1980 Johnson 70. Perfect idle, dies at speed?

Hi Spam,<br />I have a Johnson 70hp 1976 with what appears to be the same problem. It runs fine under no-load. However, when under load it will do no more than 1000 rpm, (about 5 kts). I have tried removing the link between the carbs and activated them individually when the motor is running, but they all seems to work. Furthermore, I have replaced the spark plugs, the fuel pump, and the fuel lines (the fuel pump membrane was leaking a bit and the fuel lines where also partly restricted). I have also inspected the carbs but they looks fine. <br /><br />I am now thinking of replacing the electronic ignition box since that seems the only thing left. Any opinions?<br />/petkr

 

[SpamPutney]

Re: 1980 Johnson 70. Perfect idle, dies at speed?

Thanks for all the suggestions. I'm gonna give them a try today, and I'll let you know how I make out.

 

[SpamPutney]

Re: 1980 Johnson 70. Perfect idle, dies at speed?

Well, I disconnected the top spark plug, and the engine idle remained constant. Repeating the experiment with the other 2 plugs led to the engine quickly dying. Then, I reconnected all 3 plugs, started the engine, and covered the top cylinder with my hand. No change. Covering the other two two immediately caused the engine to sputter. So I think that I can safely conclude my problem lies somewhere in the top cylinder. Now I need only determine if it is a spark problem or a fuel problem. I'm planning on replacing all the coils; they are cheap enough. Any other suggestions? Thanks

 

[DJ]

Re: 1980 Johnson 70. Perfect idle, dies at speed?

Spam,<br /><br />How is the compression that cylinder?

 

[SpamPutney]

Re: 1980 Johnson 70. Perfect idle, dies at speed?

DJ,<br /><br />All cylinders are at 155.

 

[NES]

Re: 1980 Johnson 70. Perfect idle, dies at speed?

I had a similiar problem on my 1968 55hp Johnson. After replacing and repairing numerous things I discovered the culprit by accident. Motor would run great with the muffs on. Increase load on prop and it would sputter. While on the water I was switching tanks. I noticed the bulb had flattened out. A loose part in the bulb had broken loose and would clog when the motor was drawing hard causing fuel to be restricted. I replaced the bulb again (the one that had cuased the problem was new) and the problem vanished.

 

[angus63]

Re: 1980 Johnson 70. Perfect idle, dies at speed?

You can swap coils and eliminate the possibility it is not the coil. But from your sypmtoms, sure sounds like #1 ain't got no zap. You can put some premix in a spray bottle and shoot some in #1 and listen for a change. The above mentioned should tell you which way to look. Good luck

 

[SpamPutney]

Re: 1980 Johnson 70. Perfect idle, dies at speed?

I haven't received the new coils yet (Ebay) but now I'm wondering if that is the problem. I tested the spark in the cylinder---it seems to be strong. Spraying premix into the carb does nothing at all. When covering it with my hand, there is strong vacuum. However, covering it does NOT affect the engine idle whatsoever. If anything, the motor seems to run a little smoother with the spark plug for #1 disconnected.<br /><br />Any suggestions are greatly appreciated....I simply can't afford to pay a mechanic for his time. I spent big $$$ rebuilding my boat this season--new stringers, floor, seats, wiring, etc. Never expected to have engine trouble. Very frustrating.

 

[petkr]

Re: 1980 Johnson 70. Perfect idle, dies at speed?

I spoke to a guy at the workshop by the marina and he said the power pack can be responsible. Apparently it can sometimes give spark but at irregular times, if faulty. Anyway he have ordered one that I will get anyday. I keep you posted on the development.

 

[SpamPutney]

Re: 1980 Johnson 70. Perfect idle, dies at speed?

Petkr,<br /><br />Thanks, let me know how you make out. I still haven't received my new coils. I'll let you know how I do.

 

[SpamPutney]

Re: 1980 Johnson 70. Perfect idle, dies at speed?

Received the new coils yesterday. Replaced the one I think is faulty. Engine sounds good....I think that fixed the problem. As soon as it stops raining, will go and sea test it. Wish me luck!

 

[SpamPutney]

Re: 1980 Johnson 70. Perfect idle, dies at speed?

Mission accomplished! After replacing the suspect coil, she was up on plane in no time, and zipping along faster than I remember in a long time! Afterwards, I replaced the other 2 coils, and though I have yet to sea test it, the engine sounds markedly better than before. I've seen coils (new) on Ebay for $20 a piece....good luck Petkr.

 

[petkr]

Re: 1980 Johnson 70. Perfect idle, dies at speed?

Thanks for your input. I just got a new powerpack yesterday but that did not do the trick. I return it today and look further.

 

[petkr]

Re: 1980 Johnson 70. Perfect idle, dies at speed?

I was back today to try to figure out what was wrong. With my dad pulling the choke lever slightly on the engine we discovered we could get to get about 2200 rpm under load, not much but originally I could only get 1000rpm. After running that way for about 10 minutes I could get 2000rpm without choke, but running another 20 minutes did not bring any improvments. (I had put some carborator cleaning in the fuel). I have pulled apart the carbs but found nothing wrong. I also responses equally on each carb when activated manually (link detached). I am fresh out of ideas now. A remote possiblity could be the reed valves. Anayone have any ideas?

 

[SpamPutney]

Re: 1980 Johnson 70. Perfect idle, dies at speed?

I had originally had a mechanic look at my engine, and his suggestion was the reed valves. It wasn't, in my case, but it sounds like a good guess for you.

 

[FreshwaterDrum]

Re: 1980 Johnson 70. Perfect idle, dies at speed?

I have a 1983 70 hp Johnson that gave me problems that sound similar. On a few occasions, I could get it up to full throttle, but only long after I had been running at essentially idle speed. In my case, replacing the fuel pump finally fixed the problem. Took awhile to figure it out though...

 

[Cut n' Jump]

Re: 1980 Johnson 70. Perfect idle, dies at speed?

I had the same problem as petkr once. The main jets were clogged in a way you couldn't see. It was the 1st time out that year and a residue evenly built up on the mains. It revved only when choked. A wire from an old spinnerbait cleared the varnish off the jets and saved the day. The carbs didn't have to be removed.