Johnson 115 spl Dies at idle misses at planing speed

[j_johnson33]

I have a '98 Johnson 115 spl I can get it started but have to leave it at high idle ( above 1000 rpm) if I lower to the standard netral idle it sputters and dies. I was able to get it out this weekend and on plane, at first it ran fine but then started to miss real bad while still on plane. As I brought it back to the no wake zone I had to keep it idled up to get it back to the ramp. If I would pull it back to neutral it would die. Where should I start looking? The boat ran just fine 2 weeks prior at that time the plugs were replaced along with the water/fuel seperator. Tested the coils and wires with and ohm meter and were fine. Is there a conventional way to test the power pack without special tools? I keep the boat near the lake ( saves on towing). Would appreciate any tips or advice so i know what to pack (tools, parts) for the next trip down this weekend. thanks

UPDATE!!

Checked compression all 4 cylinders were at 105 psi
I had spark at each, replaced the fuel lines, Pulled each plug wire one at a time while keeping it running, the top two plugs killed about killed the engine when removed the botton two had a minimal change. I would expect the lower carb is my problem. I'll pull them off on my next trip.
Although it will be an adventure, the ramp is about a mile away via "no wake zone " and I can barly keep it running at an idle speed. I'm not brave enough to remove carbs while it's hanging in a slip above the water.

 

[jtcarter]

Re: Johnson 115 spl Dies at idle misses at planing speed

Go through the basics, check spark, pull plugs one at a time and listen for rpm drop, go through your fuel system check for air leaks, check filter, check primer bulb. If you can't find anything obvious probably time for some new carb kits.

 

[R.Johnson]

Re: Johnson 115 spl Dies at idle misses at planing speed

On a problem like this, you start at the beginning, compression, ignition, fuel. You need proper information, "service manual". At least basic tools'. These systems must be checked one, by one. Tell us what you have to work with, and we can hopefully guide you along.