1988 Johnson 110 Misfire and cooling issue.

[AEROCOOK]

My 1988 110 Johnson runs great at one quarter throttle and above but when cruising at very low speed or taking off after it has been run at slow speed it has an annoying mismire.
I have checked the timing,, done a link and sync and cleaned the carbs but the problem persists.
Today while cruising the river with my 12 year old son at the helm The misfire began so I instructed him to maintain the current speed (still misfiring) for a few minutes then I reached over and turned the key off and pulled the plugs out to see if I could identify the affected cylinder.
What I found was that the 2 port side plugs were wet, black and oily while the 2 starbord side plugs were the desired brown / tan colour.
I also found that the port side head was noticeably hotter than the starboard side but I could still hold my fingers on it for 3 to 5 seconds and no alarm sounded so it wasnt over heated. Next I put the plugs back in, took it for a 5 minute cruise at 4500 RPM and repeated the plug check procedure, this time the head temperatures were even and the port plugs were brown and dry.
I dont know if the misfire and the cooling thing are related so that is my first question. My second question is simply what could be the cause of this (or these) problems?

 

[reeldutch]

Re: 1988 Johnson 110 Misfire and cooling issue.

a motor that runs to cold with a stuck open tstat mifgt foul the plugs and causing misfires.

when it misfires rev it op in neutral for a minute at 3000 rpm put it back in idle and listen to the motor.
it should take a minute or 2 before it starts misfiring.

 

[AEROCOOK]

Re: 1988 Johnson 110 Misfire and cooling issue.

Wow, fast reply reeldutch!
I was just editing the post to add additional info when your reply came in.
I agree with your assesment but it is the hotter bank that has the fouled plugs. I have done as you suggested, and the motor does clear it's self out after a few seconds at higher RPM, in fact I have to be careful with the fast idle lever cause when all the plugs suddenly begin firing again, the motor almost over revs.

 

[emdsapmgr]

Re: 1988 Johnson 110 Misfire and cooling issue.

You need to determine if it is overheating when on plane or at idle. A faulty thermostat can cause an overheat at idle. When on plane, the pressure relief valves open up and flood the powerhead with extra cooling water, disguising a possible closed stat. There are two stats, each controls the temp for each side of the block. If you have not replaced the stats lately, might be time to open up the housing and replace them. The wet plugs could indicate no spark to those cyls. Check the spark by putting an inductive timing light on each plug wire when the engine is running under load. Check for misfires and no fires this way. Or you can pull the spark plug boot off each plug one at a time and see if the engine rpm changes.

 

[AEROCOOK]

Re: 1988 Johnson 110 Misfire and cooling issue.

You need to determine if it is overheating when on plane or at idle. A faulty thermostat can cause an overheat at idle. When on plane, the pressure relief valves open up and flood the powerhead with extra cooling water, disguising a possible closed stat. There are two stats, each controls the temp for each side of the block. If you have not replaced the stats lately, might be time to open up the housing and replace them. The wet plugs could indicate no spark to those cyls. Check the spark by putting an inductive timing light on each plug wire when the engine is running under load. Check for misfires and no fires this way. Or you can pull the spark plug boot off each plug one at a time and see if the engine rpm changes.

Thanks for the good advice emdsapmgr. As mentioned. the motor was not overheating but the temperature difference between banks is reason for concern so I guess I will pick up 2 thermostats and gasket and get-r-done... Its a bubble back so it should be a lot of fun. (for my neighbors that is while I put on an entertaining display)
Tracking down the misfire shouldnt be too hard I hope. If the timing light indicates no or inconsistant spark I will start by swapping the plug wires from side to side to see if the problem follows to another cylinder.
I read in another post that a blown base gasket could cause poor running conditions. I do occasionally see a little bit of blackish oil film seeping down the leg from underneath the plastic skirt piece. Is this reason for concern on a V4?

 

[emdsapmgr]

Re: 1988 Johnson 110 Misfire and cooling issue.

The black tar leaking could be the start of a base gasket that is in the process of failing. A common, non-critical failure, but it will leak exhaust gas and the oily residue into the cowling. This will continue to get worse with age. Eventually, the exhaust smoke in the cowling will get so bad it will get sucked into the carbs and can cause running issues. The gasket is not much, but you have to remove the powerhead to replace it. A 2-3 hour job.

 

[AEROCOOK]

Re: 1988 Johnson 110 Misfire and cooling issue.

The black tar leaking could be the start of a base gasket that is in the process of failing. A common, non-critical failure, but it will leak exhaust gas and the oily residue into the cowling. This will continue to get worse with age. Eventually, the exhaust smoke in the cowling will get so bad it will get sucked into the carbs and can cause running issues. The gasket is not much, but you have to remove the powerhead to replace it. A 2-3 hour job.

Next time Im at the lake I will take a good look at the top of the leg and maybe remove the plastic skirt to see if I can find the source. Sounds like a winter project for one of those rare days when Im not fixing snowmobiles.