1982 90hp Johnson will not idle properly. Thermostat?

[ihc220]

I have an 82 90 hp Johnson J90TLCNB. I have rebuilt the carbs, replaced one ignition coil, have checked for spark and have a good strong spark that will jump a 1/2 inch gap. I cannot get this engine to idle properly. It starts good and runs ok for a while but the engine will stall at idle and when putting it into gear. to me it seems like an ignition issue because the engine cuts out abruptly, and does not slowly die out like it would if it were starving for fuel. It seems to idle ok cold or right after a full throttle cruise, but after a while it starts to pop and miss, and eventually stalls out.

http://www.youtube.com/watch?v=lCKvdCKrC4w&feature=youtu.be.

In the video, it is idling very fast because that is the only way that it will run in the water. The top two spark plugs look normal, however the bottom two are totally soaked with fuel. Also even when the engine has warmed up the block is only warm to the touch, not hot. I have read on this forum that I should not be able to put my hand on it for more than a few seconds, it is definitely not that hot. Are faulty thermostats part of my problem? If the engine never gets warm, could this be why the bottom two plugs are so wet or is there another reason?

 

[boobie]

Re: 1982 90hp Johnson will not idle properly. Thermostat?

What's the compression on it ?? And yes, it also sounds like you have a thermostat prob.

 

[ihc220]

Re: 1982 90hp Johnson will not idle properly. Thermostat?

I just checked compression today, 120 on all cylinders.

 

[emdsapmgr]

Re: 1982 90hp Johnson will not idle properly. Thermostat?

You may want to recheck for spark when you have the boat fully warmed up and floating in the lake. Check the spark when it is idling in gear at the dock. An inductive timing light works well for this test. The flashes from the gun will show what is going on with the spark on each plugwire.

 

[ihc220]

Re: 1982 90hp Johnson will not idle properly. Thermostat?

Ok, I will have to get a timing light and check, right now I have a strong spark on each cylinder and I can't see evidence of an intermittent spark just by looking at it, but maybe the timing light will tell me something else. I ordered new thermostats as well. I have a spare coil and powerpack but right now the spark looks good so I don't know where to start. Thank you for the help so far.

 

[boobie]

Re: 1982 90hp Johnson will not idle properly. Thermostat?

What's a strong spark ? Will it jump a 7/16 " open air gap ??

 

[ihc220]

Re: 1982 90hp Johnson will not idle properly. Thermostat?

Yes with a small bolt stuck in the plug boot and
Holding it away from the motor, it jumps 7/16-1/2 inch gap with a
Snappy blue spark

 

[ihc220]

Re: 1982 90hp Johnson will not idle properly. Thermostat?

Ok, I had the boat in the water, in gear, with the timing light on it. To me it looked like a steady strong spark on all four cylinders until it starts missing and stalling. The spark is steady, then stops completely, but it does this on every cylinder, which leads me to think that it is something ahead of the coils and powerpacks, maybe something underneath the flywheel, like the stator or timer base? Any ideas? Thank you for your help.

 

[emdsapmgr]

Re: 1982 90hp Johnson will not idle properly. Thermostat?

You've got some expensive components there. I'd agree that the problem may be upstream of the packs. Unlikely the coils. That engine has twin power packs-one controls the spark on each head. You can swap them and see if any firing problem moves to the other head. From your description, the firing stops suddenly on all cyls, so probably not either power pack. If that swap made no difference, then you are back to looking at the stator and timer base. There are some really good ignition diagnostics at cdielectronics.com. Starting around page 35, there are some good output test voltages from the ignition system. You'll need a special peak-reading voltmeter to read these voltages properly. A factory service manual should have condemning output voltages from the ignition side of the stator and the timer base when cranking the engine.

 

[ihc220]

Re: 1982 90hp Johnson will not idle properly. Thermostat?

Ok, I ordered a used stator and timer base off eBay, bought a flywheel puller, and have two new thermostats to put in next time I get to my boat which is four hours away. Hopefully I am headed In the right direction. Will update soon.