Ohming the spark caps, ALL out of spec?

[Heavy Armor]

So I just finished checking the resistance on my spark plug caps, and they were all out of spec in various ways. I found here on the forum that tolerance should be between 4990 - 5020 ohms. My readings:
#1 - 5200
#2 - 5300
#3 - 5080
#4 - 4800

#1 and #2 seem way out of spec, while #3 and #4 seem close-ish, wondering if that could just be a variation in the meter itself? What would everyone recommend doing here?

For the record, I'm trying to figure out why my bike is running like crap. New plugs, freshly rebuilt carbs by Mr. Leo. Low power, bad stumbling as you lay on the throttle. Plugs 1 and 2 are darkened electrodes but weirdly clean (no buildup at all), while plugs 3 and 4 have the expected tan finish. Stumbling does not require the bike to be warm, so unless the left coil has completely crapped out, I don't think it would be the cause, but I haven't been able to dig that deep just yet to check them.

[crAKer-47]

My father told me to always check the inherent resistance of the meter by touching the probes together first. All my cheap meters read something when I do this.

[Heavy Armor]

My father told me to always check the inherent resistance of the meter by touching the probes together first. All my cheap meters read something when I do this.

I actually did this before I did any readings, and my meter showed 0 resistance. I was having some difficulty making good contact down inside the caps though. I'm not sure what part of the plug-side is actually making contact... I would have assumed all the metal bits were involved, but clearly they were not.

[crAKer-47]

Interesting. My next step would be to borrow a buddies meter and check them with his. Or have him test them and see if the readings are the same. 10% +\- (my math is usually suspect) seems to be a big difference though. The difference in the posted spec is 0.5% (same warning) I'm curious as to what mine will read now.

I'll have to check my service manual, but I believe the left coil fires cylinders 1 and 4.

[GrandpaDenny]

Check REALLY well for vacuum leaks. Those carb boots are a pain. When you're done checking, check again. Does your bike still have the hold-downs for the air filter element? If not, make some. Anything that can leak vacuum, will leak vacuum, check really really really well.

[Heavy Armor]

Check REALLY well for vacuum leaks. Those carb boots are a pain. When you're done checking, check again. Does your bike still have the hold-downs for the air filter element? If not, make some. Anything that can leak vacuum, will leak vacuum, check really really really well.

The carb boots were indeed a PITA. I tried to look and make sure everything was in place, but I'll give it another look. I've tried several rounds of spraying starting fluid around to see if it's picking anything up, but it never made any change.... that was right after the carbs though, I haven't tried since this stumbling started. Maybe something worked loose, or is only happening at the higher RPMs when the vacuum increases.

[Heavy Armor]

I'll have to check my service manual, but I believe the left coil fires cylinders 1 and 4.

You're correct, it's 1 & 4 and 2 & 3 paired. I dunno why I assumed it was 1 & 2 and 3 & 4. That makes the plug colors even weirder.

[GrandpaDenny]

The carb boots were indeed a PITA. I tried to look and make sure everything was in place, but I'll give it another look. I've tried several rounds of spraying starting fluid around to see if it's picking anything up, but it never made any change.... that was right after the carbs though, I haven't tried since this stumbling started. Maybe something worked loose, or is only happening at the higher RPMs when the vacuum increases.

Spraying starting fluid was inconclusive after a while for me, but when I felt around the boots I found one of the lips folded over. I got to be pretty good at installing those boots after doing them a number of times. There is a notch on them that indexes them to the airbox. That was an interesting discovery. Getting the notch seated right made them so much easier to install. Also, the string trick works miracles - before installing the boot, lay a string in the groove. Start the boot lip in where the string overlaps, pull the string out around the boot, and voila. Just like putting in old rubber mount windshields and pickup truck rear windows (which is where I learned the trick).

[Nails]

I've tried several rounds of spraying starting fluid around to see if it's picking anything up

I've had better luck spraying WD-40, which causes a stumble when inhaled.

I got to be pretty good at installing those boots after doing them a number of times.

Me too. I put the boots on the airbox and engine (all clamps in place, appropriate ones tightened), and then cowboy the carbs between them. A long, skinny screwdriver can guide boots over and on-to the carbs. A stiff rod (I use 1/8" welding rod) with a 1/2"-end bent 90-degrees can help uncooperative boots straighten up and fly right. A little vaseline works wonders when inserting things (the carbs *) into tight places (the boots *) ... and especially for putting the fuel line back on that floppy Tee. Stout, extended-length, needle-nose pliers have come in handy.

I already nominated this as the most sucky job working on XIIs.

* For the benefit of those prone to wandering off topic.

[GrandpaDenny]

For the benefit of those prone to wandering off topic.

Wow, I really must be losing it. I didn't wander off topic. I took you seriously. Every word.

Somebody send me help!



I used WD40 silicone spray on my boots, IIRC. They were also brand-new boots. What a pain. I think you're right, Nails, replacing the carbs has got to be the worst job on the bike. I remember before that I thought the spark plugs were the worst, but moving the cruise control junction and having a nice long set of spark plug wire pliers makes that job a piece of cake, and indeed the bike's tool kit's spark plug socket is the best tool to use to replace the plugs.

On a side note, I'd put Iridiums in Gertrude, and after 50k they were definitely worn. I probably could have just regapped them and put them back in, but I put in a set of stockers. Moot point now <sniff>.

[crAKer-47]

So I just checked my spark plug caps:
1-4.96K
2-4.93K
3-Dead
4-Dead
I looked all over my service manual and I couldn't find any specs on the resistance of the caps though. But, there are specs for the coils.
Primary windings-1.8-2.8 OHMS
Secondary (caps removed)-10-16K OHMS

Hope this helps, looks like I'm looking for caps myself. Or an alternative system all together. Stick coils perhaps?

[4redjf]

Check REALLY well for vacuum leaks. Those carb boots are a pain. When you're done checking, check again. Does your bike still have the hold-downs for the air filter element? If not, make some. Anything that can leak vacuum, will leak vacuum, check really really really well.

on these air filter hold-downs, what is the best material and way to make them?

[GrandpaDenny]

on these air filter hold-downs, what is the best material and way to make them?

I don't know what the original ones were made of, but I'm going to guess some kind of hard plastic. Perhaps ABS. I used some foam, pretty stiff stuff, that a bluetooth communicator had come packed in.