1984 Johnson 70hp - Poor Idle

[scrampbell]

I'll try to keep it short...

Old problem: Ran fine at idle and on muffs, bogged under load. Replaced fuel line, cleaned high speed jets (high speed jets only, did not remove and rebuild whole carb). After: Ran fine for an entire trip (2 hours).

New problem: Took the boat out for a 2nd trip last weekend. At WOT, engine hesitated for a second so I took it down to idle (I'm very afraid of overheating). Motor idled rough (idle used to be this motor's strong point) so I shut it down. Temp checked fine with laser thermometer (140F). Upon trying to restart the engine, it would die at idle. I could start it at fast idle but couldn't get it in gear without the engine dieing. So we fished right there for a couple of hours. After fishing, the engine would stay running at idle, but probably wouldn't have for long, so we headed back to the ramp. This time, it wouldn't immediately get back up to WOT... it bogged, but it was a different kind of bogging than the initial problem that was fixed by cleaning the high speed jets. In fact, this time even though it was bogging, it bogged it's way right up to WOT -- and ran fine at WOT all the way back to the ramp.

Any ideas? I cleaned the low speed jets last night and will take it out again today to test.

 

[Boss Hawg]

Re: 1984 Johnson 70hp - Poor Idle

Rebuild the carbs
FWIW i add a little Seafoam in my tank at each fillup

 

[longjohn41]

Re: 1984 Johnson 70hp - Poor Idle

I had similar symptoms with a 1983 50hp 2 cyl evinrude that was laid up for 2 years. As it turned out I had more than one issue. Cleaning all the jets cured the issue for a while for me, but a separate electrical issue appeared very soon after that. Just like the clogged jet issue, the engine idled badly and generally died when you put it in gear, but it could be just-about coaxed to keep going if you backed off and on again a few times. If you could get to WOT it ran well.
The electrical issue I had was a corroded/ sometimes disconnected wire in the 4-terminal connector plug that connects the power pack to the charge coil under the armature plate. As soon as I repaired this, the issue was gone. I think that this is a likely area for an intermittent issue as these wires move everytime you push throttle. It was interesting that the electrical issue caused the very same symptoms as the clogged jets. (my interest had mostly worn off after I had taken off and cleaned the carbs five times in a row, thinking that it surely the jets that were clogged again)
I didn't have a spark tester but the spark looked ok with a plug removed and cranked over. Maybe the bad wire was connected while I was checking. Finally I went through the electrical troubleshooting in the manual which uncovered the disconnected wire
When cleaning jets with an aerosol cleaner, I found that looking into the carb barrel to confirm that the spray is actually getting through was important as the slow idle jets are tiny and take a lot of cleaning if badly clogged. Make sure also that the slow and medium idle jets haven't been swapped at some point. Hope this helps. Cheers

 

[Home Cookin']

Re: 1984 Johnson 70hp - Poor Idle

I had a similar problem with an electrical short from frayed insulation acting excatly like a fule path issue. OB's are wierd that way.

You sound like a carb/ethanol issue, one I have fought for a while now. However, my 1988 70 just died over the weekend from water entering the cylinders, probably from a failed exhaust baffle. Ran great at WOT then bogged as if out of gas; restarted once or twive and repeated; never restarted after that but came close. Hope yours isn't that serious, and probably isn't.

 

[tashasdaddy]

Re: 1984 Johnson 70hp - Poor Idle

a lot of the problem is cause by Ethanol, the old lines are deteriorating due to ethanol, they then start to sluff off and contaminate the carbs. settling in the bottom of the carb bowl. this clogs the pickups for low and high speed jets.

it takes a total cleaning, and rebuild kits, while there replace all fuel lines with B1 rated alcohol resistant lines. besure to flush lines before connecting to carbs.