93 Johnson 120 Stumbling

I have a 1993 Johnson 120 with a problem. The best way I can describe it is that it stumbles. <br /><br />It starts right up, sounds good then it's as though the electricity is turned off for an instant. A puff of smoke comes out of the exhaust then it sounds good again. This "stumbling" happens maybe 10 to 15 times a minute. I can feel the stumbling at higher RPMs as well.<br /><br />I just got it back from the shop where they said they'd fixed the problem with a new power pack but the problem is still there. I think I learned a $260 lesson.<br /><br />Looking from behind the engine the left bank of plugs plus the top right plug look the same, a little wet but not fouled. The lower right plug is dry but black and sooty.<br /><br />I noticed yesterday that when the engine stumbles the fuel gauge acts as though the ignition was switched off, it goes to "E" then rebounds when the engines fires again.<br /><br />Any help and/or advice is greatly appreciated.<br /><br />TIA<br /><br />Tim

Re: 93 Johnson 120 Stumbling

Hi HogFan the first thing I would do is a compression test on all cyl's then check all wires make sure there tight do a spark test make sure you get atleast jumps atleast 7/16in blue spark someone else will be along with more advise good luck

Re: 93 Johnson 120 Stumbling

hello<br /> to find this problem will take some understanding of how the ignition system works. myself I would break out the ol CD-77 multimeter and find the problem. if its a continual problem it should be found in less than an hour. use a seperate keyswitch/harness assy (break out box) to eliminate the wiring from the engine to the hull. if the problem goes away with a "breakout" box you just eliminated the engine as the source.<br />with the engine running there is aproximatly 200V on the black/yellow kill circuit. if it arcs to the 12v side it will shut down the ign. if it arcs to the ground side it will kill the ign. does the tach needle jump as well? any tests you make will require an analog meter as a DVM wont respond fast enough to find momentary breaks.

Re: 93 Johnson 120 Stumbling

That's a good place to start. Compression on all cylinders should be within 10 to 15% of each other...psi wise. All sparks should be thick and hot and jump at least a 1/2" gap. <br /><br />Has the carbs been overhauled lately?<br /><br />Check the little recirc hoses running around the engine. Make sure they are all good with no leaks. Same with the fuel lines....especially the ones for #3 hole. Fuel lines should be plyable and not hard.

Re: 93 Johnson 120 Stumbling

First, I want to thank y'all for all the advice/help. This place is just a wealth of information.<br /><br />I checked the compression and on the left bank both are right at 120 and on the right bank both are right at 117.<br /><br />The spark jumps the 7/16" gap with a nice pop and in full sunshine I could see the spark.<br /><br />I hooked up my timing light to each cylinder and lo and behold I found one (lower right) that would skip flashes intermitently. <br /><br />I decided to see if I could move the problem so I swapped the coils on the right bank but the problem stayed on the lower cylinder. I cleaned and buffed the surface of the block as well as the (for lack of the correct term) grounding surfaces on the coils.<br /><br />I did notice the grounding surface where it enters the coil was a bit rusty on the lower coil.<br /><br />Next I swapped the plug wires on the right cylinders and the timing light never skipped a flash again and the engine stopped stumbling.<br /><br />Do y'all think the problem might be in the wires or the coil?<br /><br />Once it gets dark I'm going to go out and restart the engine to see if I can see any arcing.<br /><br />Again, thanks for all y'alls help.

Re: 93 Johnson 120 Stumbling

It sounds to me like you fixed it. Do you have the old power pack? It may still be good. Good luck with it.

Re: 93 Johnson 120 Stumbling

I think the grounding areas may have been the problem. Only way to really know is put her in the water and see what she does. If she runs as good as advertised, you got a good fix. If not, we'll go back and look at what ya' did to get the temporary fix and go from there.<br /><br />Keep us posted....your fix could help someone else out in the future.....Thanks!