Fouling Plugs? Check the battery!

[chnpostal]

My 99 Road King just decided to start fouling plugs. Seeing as how I converted it over to carb recently, that's where I laid the blame. Of course nothing was wrong with the carb, and I learned something new.

The battery, when it only has a couple of bad cells, can turn the motor over just fine. You'll even get a spark from the coil.....just not enough to start the engine. It'll be just enough spark to make it spit and backfire, and foul the snot out of the plugs in short order. This same battery, when fully charged, would act just fine even under load......but after sitting for 2 days, it would drop to almost 8 volts when the starter was engaged. Enough to spin, but not enough for a good spark. I really hate stuff that just "partially" fails.

Thanks LittleBear for your help in chat.....if that carb wasn't good before, it is now!

He is the Knower of Stuff... just sayin'...

Great tip, thanks.

[LittleBear]

Man, that is a new one on me but it does make sense. All the batteries I have had fail would not turn over the motor, so I had never seen that one.
Thanks for posting the solution. New data is always welcome.
Glad you got her fixed and running right chnpostal.

[Berserker]

never heard of spark, but not enough spark. Been running sleds for years. If the spark wasn't good, usually bad plugs.

I guess anything is possible. Did you get the insufficient spark with new plugs?

I think they have lights you can clamp on, to see if good spark. I have always gone by if you can see it ok. Maybe its not ok.

[Berserker]

I think I fouled some plugs last year, but I had an intermiten ignition problem. So don't know what came first. Also had some pinging early that weekend. To many variables to say for sure.

[chnpostal]

Hey Beserker, just to clarify a little, I don't know if it was "not enough spark" or if the voltage drop caused a very intermittent signal from the ignition. When it wouldn't crank, I just used a new plug, put the plug wire on it, grounded it and turned the engine over. It had what appeared to be a good spark, and I was just checking to see if it was firing.

When it fouled out the second set of plugs, just on a whim I put a digital voltmeter across the battery and hit the starter. The voltage dropped from 12.5 down to 8.2 while cranking. I don't know the specs on a Crane HI4T/C, but it probably needs more than 8.2 volts for proper operation. After fully charging the battery, cranking it would only drop to 12.1 volts. Took it for a 20 mile ride, checked the plugs, checked cranking voltage, and everything was OK. I also removed the negative battery wire and checked for current draw when off......there was none, so all seemed well. After not riding for 2 days (rain and high winds here), I went out to start the bike up and it wouldn't crank. It usually cranks up immediantly when right, so I didn't try any further. Instead I looked at the plugs....they were just slightly wet, but not fouled yet. Put the voltmeter on the battery, turned it over, and there it was....8.2 volts again.

Battery is showing signs of a dead cell, but it takes a full charge, 2 days to bleed down, and is still able to spin the engine? That was a new one on me, too LittleBear.

[LittleBear]

Just as a point of clarification.
A plug can have spark when out of the hole but not enough when under compression to fire. Very similar to what happens with a bad coil that is not totally gone. It will run just fine under light throttle and at most speeds, but when you go WFO, the added cranking pressure blows out the weak spark and you get a miss or a non firing cylinder.
The modern ignitions tend to be very voltage sensitive since they are taking reading from a number of sources. Low voltages give weak input signals and weak supply voltage and can cause strange things to happen.
I understand why you looked at the carb first. Murphy says, the that thing you messed with is the first thing to screw up.

Originally Posted by chnpostal

Hey Beserker, just to clarify a little, I don't know if it was "not enough spark" or if the voltage drop caused a very intermittent signal from the ignition. When it wouldn't crank, I just used a new plug, put the plug wire on it, grounded it and turned the engine over. It had what appeared to be a good spark, and I was just checking to see if it was firing.

When it fouled out the second set of plugs, just on a whim I put a digital voltmeter across the battery and hit the starter. The voltage dropped from 12.5 down to 8.2 while cranking. I don't know the specs on a Crane HI4T/C, but it probably needs more than 8.2 volts for proper operation. After fully charging the battery, cranking it would only drop to 12.1 volts. Took it for a 20 mile ride, checked the plugs, checked cranking voltage, and everything was OK. I also removed the negative battery wire and checked for current draw when off......there was none, so all seemed well. After not riding for 2 days (rain and high winds here), I went out to start the bike up and it wouldn't crank. It usually cranks up immediantly when right, so I didn't try any further. Instead I looked at the plugs....they were just slightly wet, but not fouled yet. Put the voltmeter on the battery, turned it over, and there it was....8.2 volts again.

Battery is showing signs of a dead cell, but it takes a full charge, 2 days to bleed down, and is still able to spin the engine? That was a new one on me, too LittleBear.

Thanks a million for the heads up, been having some starting problems and have fouled plugs as a result! I have a known suspect battery. It does seem to spin right up and actually start when fully charged with new plugs...

HMMM, at least gives me another place to look and consider....