lost 2nd cylinder/ fouling question

was having trouble starting yesterday, so i was checking stuff out on the bike. besides the tach cable unscrewing itself from the tach (odd) i was checking the plug cables and the wire pulled out of the cap. It must have loosened itself sometime during the day, but since then it hasn't been idling right. once warm, it'll sit around 1k rpm, and then fall down and die unless i give it throttle. I screwed the cap back into the wire, but the idle problem persists. i'm not sure if i'm running on 3 cylinders. could i have fouled the plug by riding a few miles without spark in that cylinder to the point that it won't spark now? and would my idle problem be a symptom? i know this would look like a carb issue, but it idled fine yesterday morning.... saturday i'll have some time to diagnose a little, but until then, any ideas?

thanks

kellen

 

I would definately take a look at the plug. It probably is fuel fouled. Take it out and clean her up. This could definately be the cause of the bad idle. Happy troubleshooting.

 

that was my hypothesis....i'll pull stuff out and test it tomorrow morning if i can. thanks for the reply....

kellen

 

The first 82 Maxim 550 I owned had the same problem wtih the cable unscrewing, but with the spedometer. I needed to have someone get at it with a wrench finally to get it to stay put. My newest and most recent is waiting for the tach cable to re-attached.

To clean up a fouled plug, how should one go about it?

Timetonut
j0~

 

As a rule, if the plug is fuel-fouled, through it out. The plug will cause you fits if you try to save it. (I'll explain in a moment.) However, if it's just dirty, you can wirebrush it off and reuse it most of the time.

I'm going from memory here so my numbers may be off, but the reasoning is sound. Under normal conditions, it will take a spark of x volts to jump a gap of y millimeters at one atmosphere. What is happening is that the air between the anode and the cathode ionizes and creates a path for the electrons to traverse. The wider the gap, the higher the voltage required. In addition to this, if you increase the atmospheres, say under compression (10:1), you will also need to increase the voltage to ionize the air. Here's where you run into trouble: a fuel-fouled plug will spark all day long at one atmosphere, but as soon as you up the cylinder pressure, it fails. What usually happens is the spark encounters so much resistance between the anode and cathode that it hops to the fuel-soaked porcelain insulator to ground, i.e. no spark. Let the hair-pulling fits ensue!

Like I said, it's just better to toss 'em!

 

If someone were to wait long enough, say all day while at work, would the fuel-soaked porcelain dry itself out? Aside from the occasional shocking of myself these are a new critter to me.

Timetonut
j0~

 

My experience says no. I've only been successful at reusing fuel-fouled plugs when I've superheated the porcelain with a propane torch. You basically have to burn off the fuel that leached into the pores of the porcelain. Again, just easier to grab another set from the parts store.

 

I think the tack cable unscrewing is common, has happened 2 times to me now, so I try to make sure to check it out every few days.

 

bingo on the fuel fouled plugs...just toss them.

And as for the tach cable unscrewing, my 82 550 always unscrews from the engine side. I always have to tighten it up or I throw the cable while I cruise down the road...Don't need that to happen again.

 

I've been runnig a set of plugs where 3 of the 4 were fuel fouled early in the spring. More than 2k miles with no problem.

I cleaned them by shooting each plug with just a shot of starting ether. Shake off the excess (if they slip out of your hand they are ruined). Put in the bike and fire up. No problems.

Oh, mine wouldn't spark outside the bike either. Only way I got a spark was when the base of the plug was 1/4" away from ground. Then I built enough voltage to fire them. Don't even ask how much screwing around before one happened to end up that far away from ground.

 

I'd say your analogy of the porcelain is spot on save one point. ALL ceramic insulators are glaze fired and are no longer pourous. They are as a china plate, a glass finish.
Now having said that, I haven't had any problems with reusing fuel soaked plugs, just let them dry out or shoot them with WD-40.
Where I have seen problems is where someone uses a sandblaster to clean the plug and fails to clean the blasting medium out of the plug. Simply madness, not worth the risk to your motor. $8 buys a fair piece of mind.