1999 Johnson 70hp quits in idle

[nim713]

Having issues with my outboard at stalling at idle. Both in the water and with muffs on. When I start it, it fires almost right up everytime and idles at 1000 rpms, when it cools down it drops to around 400 rpms but dies almost immediately. When i turn the key again it starts right up and goes back to 1000 rpms but dies when the rpms drop again. Any thoughts on whats going on, is there a adjustment that can be made? Any help appreciated, Im taking my nephew fishing for the first time and would like no issues. Machanic says its a 1 month wait to pull it in.

 

[racerone]

Do a compression test first.

 

[nim713]

Compression on cylinders are 137, 136, 137

 

[Joe Reeves]

Nim... Is this engine new to you OR have you owned it awhile. If owned awhile, when is the last time it ran as it should... and since then, has any work been done to it... and if work has been done to it, did this problem suddenly appear directly after?

1000 rpm is a correct idle rpm if running on a flushette... there is no way that engine will idle at 400 rpm.

You say that in restarting the idle is once again 1000 rpm. Is that all you do... simply turn the key to start... or... do you go thru the priming the fuel primer bulb sequence once again?

Try having someone pump the fuel primer bulb constantly, acting as a manual fuel pump to see if that cures the problem.

Also, I'm wondering if that engine has the "Fast Start" feature whereas the timing is advanced electronically, then dropped to normal timing when the engine warms up? If so, perhaps someone set the idle with the "Fast Start" feature still engaged.

 

[nim713]

Ive had it for a few years now. It had the carbs rebuilt and gone through. It does have the fast start on it. And what you described is accurate. Once its warm the engine drops idle, it used to hold and run at about 500 rpms but now it just quits like you turn the key off.

 

[nim713]

Is it possible that the power pack is going out?

 

[Joe Reeves]

Nim... Do all spark plugs look identical when you remove them? Describe them as best you can, especially if there is a difference. Keep track as to what plug comes from what cylinder.

The compression looks good. Now, with all spark plugs removed, check to see that the spark will jump a 7/16" air gap with a strong blue lightning like flame... s real SNAP! NOTE that the 7/16" air gap is important!
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(Spark Tester - Home Made)
(J. Reeves)

You can use a medium size philips screwdriver (#2 I believe) inserted into the spark plug boot spring connector, then hold the screwdriver shank approximately 7/16" away from the block to check the spark or build the following:

A spark tester can be made with a piece of 1x4 or 1x6, drive a few finishing nails through it, then bend the pointed ends at a right angle. You can then adjust the gap by simply twisting the nail(s). Solder a spark plug wire to one which you can connect to the spark plug boots, and a ground wire of some kind to the other to connect to the powerhead somewhere. Use small alligator clips on the other end of the wires to connect to ground and to the spark plug connector that exists inside of the rubber plug boot.

Using the above, one could easily build a spark tester whereas they could connect 2, 4, 6, or 8 cylinders all at one time. The ground nail being straight up, the others being bent, aimed at the ground nail. A typical 4 cylinder tester follows:

..........X1..........X2

.................X..(grd)

..........X3..........X4

This can obviously be modified to a 6 or 8 cylinder setup tester.
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