1990 Johnson 88 SPL - won't idle at low rpm - VERY INTERESTING!

[shippro]

VERY VERY INTERESTING SYMPTON!!!
I overheated the motor last month for a couple of minute so I had to replace impellar and head gasket.
The compressions are around 85 psi for all 4 cylinders. I checked spark for each cylinder. Cleaned carbs completely. Using non-ethanol gas. Installed new spark plugs and starting motor.
The motor starts OK with muff water but it dies around 1000 RPM so I had to increase idle speed up to 1300~1500 RPM by idle adjustment to keep the motor running with muff water. When I first adjusted the idle adjustment screw, I had to increase it to maximum but still was not enough so I had to buy longer screw to increase idle speed. That's how I increased the idle speed.
Funny thing is the RPM jumps and downs little bit itself and stalls the engine sometime. I checked temperature. The port cylinders get 105 degree and starboard cyliners get 125 degree on idle speed.
When I start it on ramp, it gets harder to start and it dies at 1300 RPM so I had to keep the RPM over 1500 to keep the motor run but it doesn't run long.
I don't know what's wrong. Do you think iginition system was messed up from the overheat? I am thinking about changing all ignition system (power pack, stator, etc) becasue I have all set of ignition system from my old 88 SPL.

 

[emdsapmgr]

Cleaning carbs with non-ethanol gas won't achieve anything. Dried fuel/fuel gelatin won't dissolve in fuel. You have to use a real carb cleaner, such at that available at an auto parts store. Their aerosol products with the small nozzle straw are one of the best products that will do the trick. The cleaning needs to be inside the carb passages which you can't see. Make sure you remove all 3 jets for each carb barrel and inspect them for debris, clean the carbs, then reinstall them. During reassembly of the carb to the engine, it's possible one of them may not be fully closing at idle. There is an adjustment screw on the linkage of one carb to set that. If one carb is staying slightly ajar at idle, you can get up/down idle rpm's. You should only set the idle when the engine is on the boat and it's floating in the lake. You can't set it when it's on the trailer. Set the idle when the boat is floating normally in the lake and it's in forward gear. Set the idle to 650-700 rpm's. If you later run it out of the water on the trailer, you will see the rpm's will be perhaps 1200-1300 rpm's. That's normal since there is no backpressure on the prop exhaust. I'd think the 125 is a normal idle temp, the 105 is probably too cold, and may indicate that the thermostat on that side is stuck in the open position. If you change it, might as well replace both of them at the same time. If the engine runs fine at WOT, the ignition system is probably ok. This variance in head temps is probably not related to your idle issues.

 

[schematic]

may also be the aftermath of an overheat. how did the cylinders look when you were changing the head gaskets? 85psi is low....

 

[racerone]

Guessing and throwing parts at it is not a good method of doing repairs.------Start with some simple trouble shooting.---------Are the orange wires going to the coils on correctly, both sides must have orange blue to the top coil.