trouble with idle

[kwoolard]

I have a 1974 40HP 2cyl. Johnson. I have recently had the carb rebuilt by an outside source about 5 months ago. It ran smooth at idle, the best it ever has, as soon as I got it back and put it on the water. Here lately, it is starting to die out at idle. I have adjusted the idle speed valve out a turn and it ran fine for a few trips out. It then started the same problem of cutting of at idle. I replaced the spark plugs and installed with the right gap but no improvement. However I noticed that the spark plug tip, where the plug wire boot attaches to the plug, was loose and was a blueish color, as if it had overheated. I tightened it up and ran the engine but no improvement. I also noticed that the coil inside the plug wire boot was rusted bad, so I thought it may be a bad connection. While the engine was running (i won't be affended if you call me a fool for doing this) I tried to wiggle the plug boot to see if it was loose and was not getting the proper connection to the spark plug. Well it gave a bit of "shock" to my arm. I checked the manual and other sources and they say that the spark could be jumping through the insulation to the block and shorting out. Is this possible? What else would be causing my idle problem?

 

[Xcusme]

Re: trouble with idle

kwoolard,<br />Yes, you can get 'bit' from the business end of the plug wire. If you have a corroded plug end, it's best to clean out the plug connector to the plug. If the spring connector inside of the plug boot is corroded it can arc the voltage inside of the boot. Good, solid connections at the plug are essential for good spark and combustion. It is true that old cable insulation can breakdown , causing the high voltage to arc through the boot or wire or both to find a ground. This will kill the spark before it gets to the plug itself and kill the cylinder from firing.<br /><br />If you run the motor at night with the cover off, sometimes you can actually see the high voltage going to ground or hear a high voltage 'snap' as the voltage goes to ground. Some folks use a dry wooden stick to push against the plug wires and boots, forcing them a little tighter looking for stray arcing. You became what is known as 'The low impedance source to ground' when you got shocked. The plug ends (boots) can be removed and inspected for corrosion too, clean up any debris ,rust etc. and re-assemble. Solid clean connections and new plug wires are a must for delivering the high voltage to the plugs.

 

[kwoolard]

Re: trouble with idle

Thanks for the info Xcusme. I am not sure if you are familiar with my model but the plug wires are incorporated into the coils on each cylinder. Which in my opinion makes it impossible to replace just the plug wire. Is it possible to replace the plug wires on the coils or can I replace the spring/coil in the boot? Also, will wrapping the plug wires with electrical tape eliminate my grounding problem to the block? One more, would this also be the cause of my engine rpm fluctating slightly at full throttle? Thanks for your help!

 

[Xcusme]

Re: trouble with idle

You can replace or clean up the spark plug end of the wire but you can't replace the wire, it's molded into the coil body. If the wires are faulty due to age, it's best to replace the whole coil. The plug ends are easily removed , cleaned and re-assembled using a small amount of isopropyl alcohol. Wrapping the plug wire with electrical tape is a temporary fix at best. Moisture and age take their toll and your only viable fix is to replace. Dropping one or more cylinders can make the motor miss at any RPM. Besides the arcing issues with the plugs , I feel your problem may again be with the carb. You said that you opened the low speed idle valve a turn and the motor idle improved. This richened the mixture , pointing to the low speed idle circuit. If when idling and it starts to die, can you pull the choke a bit and see if the motor recovers? If it does recover, it's a fuel delivery problem.

 

[sdiet]

Re: trouble with idle

I hooked a timing light on my plug wires to find that one fired intermittently, the motor had overheated previously from the impeller going out and the plug wire had scored up against the top of the enginge. I did the temporary fix and wrapped it in electrical tape, working fine for now.