JD 345, 20hp Kawasaki Weird starting

[Ron_P]

I have an older JD 345 with the 20hp liquid cooled Kawaski V twin. In the past it would die after running for a short time. Then refuse to start until left sit for about an hour or so. Once it starts again it's fine, might not die again until I mow next time. Well today wife was mowing and decided to take a break. The thing ran fine for well over 2 hrs. She parked it under a shade tree. About 2 hrs later she went to finish mowing and it would not start. Cranked fine, has plenty of gas. I tried pouring a small amount of gas into the carb, but still would not start. Here's what puzzled me.

I pulled the left plug wire off to check for spark. I had wife hit the key, and it started to fire. I put the plug wire back on the spark plug, died. I had to pull it off, hold it slightly off the spark plug, and it would fire and start. Finally it did start and run. So I'm curious, why is it doing this? Spark plugs new, good fuel, new fuel filter. I've never had an engine start by removing a plug wire.

Could it be the coil is going bad? It seems to me to be an electrical problem, not a fuel. Any insight is greatly appreciated.

 

[Rivets]

What is the brand and number for the spark plug you are using? What is the model number of your engine?

 

[bertsmobile1]

It is doing that because the plug is fouled.
Voltage in a spark plug wire is not an on off situation.
It starts at 0V builds up to the theoritical maximum voltage then drops off to zero again.
Voltage determines how much resistance can be overcome.
An air gap is a resistance so the higher the volts the bigger the gap the spark can jump.

Electricity will also follow the path of least resistance which is why lightning follows a zig zag path.

When voltage starts to accumulate at the end of a spark plug it will build up until it has enough volts to ground out to the engine.
If the plug is fouled then the path down the side of the electrode is easier than across the gap.
To put some illustrative numbers to it .
To jump across a plug gap requires around 15,000 V minimum
To run down the side of a fouled plug requires around $ 3,000 V
So a fouled plug will drain the voltage down the side of the plug rather than jump across the gap.

Now if you have introduced a bigger resistance by holding the plug lead away from the plug, the voltage has already exceeded the 15,000 min required to jump the plug gap.
So when the volts get to the plug they jump the gap and ignite the charge in the cylinder.

If you were to hold the lead away from the plug for long enough, eventually whatever is fouling the plug will burn off and the engine will run properly for a while till the plug fouls again.

Now this might sound like a magic no cost fix all, but it does come with a nasty sting in the tail.
Holding the lead away from the plug & increasing the EXTERNAL resistance to the spark can make it ground out internally ( if the resistance inside the coil is lower than the external air gap ) thus shorting the coil internally and consigning a $ 50 to $ 100 part to the garbage bin in place of a $ 5.00 spark plug.
And of course there is always the chance of the resistance provided by the surface of the plug wire + your skin being lower than the air gap and you become the path of least resistance ,,, ouch.

And if you have ever wondered why your car / motorbike runs at 12 V, well the resistance of dry skin is around 15 V
Put dry finger across the terminal of a battery and you fell nothing.
Damp your hand and it bites.

This should have been taught to most people who had the good fortune of a Western modern schooling during the science classes, shame so little of it seems to have sunk in.

Your problem is what is causing the plugs to foul and how to overcome it and for that I shall leave you in the capable hands of Rivets who has started to diagnose your problem which should have been addressed a long time ago by the sounds of it.

 

[Ron_P]

What is the brand and number for the spark plug you are using? What is the model number of your engine?

I think the model number of the engine is FD611V, I use Champion 849 CJ6 spark plugs

It is doing that because the plug is fouled.
Voltage in a spark plug wire is not an on off situation.
It starts at 0V builds up to the theoritical maximum voltage then drops off to zero again.
Voltage determines how much resistance can be overcome.
An air gap is a resistance so the higher the volts the bigger the gap the spark can jump.

Electricity will also follow the path of least resistance which is why lightning follows a zig zag path.

When voltage starts to accumulate at the end of a spark plug it will build up until it has enough volts to ground out to the engine.
If the plug is fouled then the path down the side of the electrode is easier than across the gap.
To put some illustrative numbers to it .
To jump across a plug gap requires around 15,000 V minimum
To run down the side of a fouled plug requires around $ 3,000 V
So a fouled plug will drain the voltage down the side of the plug rather than jump across the gap.

Now if you have introduced a bigger resistance by holding the plug lead away from the plug, the voltage has already exceeded the 15,000 min required to jump the plug gap.
So when the volts get to the plug they jump the gap and ignite the charge in the cylinder.

If you were to hold the lead away from the plug for long enough, eventually whatever is fouling the plug will burn off and the engine will run properly for a while till the plug fouls again.

Now this might sound like a magic no cost fix all, but it does come with a nasty sting in the tail.
Holding the lead away from the plug & increasing the EXTERNAL resistance to the spark can make it ground out internally ( if the resistance inside the coil is lower than the external air gap ) thus shorting the coil internally and consigning a $ 50 to $ 100 part to the garbage bin in place of a $ 5.00 spark plug.
And of course there is always the chance of the resistance provided by the surface of the plug wire + your skin being lower than the air gap and you become the path of least resistance ,,, ouch.

And if you have ever wondered why your car / motorbike runs at 12 V, well the resistance of dry skin is around 15 V
Put dry finger across the terminal of a battery and you fell nothing.
Damp your hand and it bites.

This should have been taught to most people who had the good fortune of a Western modern schooling during the science classes, shame so little of it seems to have sunk in.

Your problem is what is causing the plugs to foul and how to overcome it and for that I shall leave you in the capable hands of Rivets who has started to diagnose your problem which should have been addressed a long time ago by the sounds of it.

Thank you for your detailed explanation on why that happens. Obviously I didn't have the type of schooling you referred to, which would have been 40+ years ago. Then again I may have, but my memory fails me now :smile:

 

[Rivets]

Kawasaki recommends a resistor plug for you engine. NGK BMR4A with a gap of .024”-.028”. This plug will provide the extra resistance Bert is talking about for your engine to run properly. This manual might also help you out.

http://www.mymowerparts.com/pdf/Kaw...90V-FD611V-KAWASAKI-SERVICE-REPAIR-MANUAL.pdf

 

[Ron_P]

I'll get a couple of those plugs and see how it likes them. Thank you very much.

 

[bertsmobile1]

When you take your old plugs out have a good look at them.
There are a thousand U Tube pages showing you what different plug conditions MAY mean with regards to the wear in your engine.
And I am 68 so it was a very long time since I was in high school, but it was a boys only school so it was easier to focus the mind on the blackboard :laughing: