off-idle stumble

[Nails]

I'm starting a new thread because it's just too much drama for the first one.

The XII is new to me, and it's never really run right. I did a lot of work (see "2017 mods/maintenance" thread), and my first ride had a miss and poor power at low RPMs and on hills. It was way rich (3 turns out), and one coil showed a short in the primary winding. I replaced that coil with a used one (wires and all), and it ran much better, especially on freeway hills and anytime above 2500 RPM.

I also started chasing the pilot screw, but I've now been too lean without getting rid of the remaining stumble. It runs best at 1.5 turns out, which makes perfect sense to me. The stumble is only 1500-2000 RPM. When leaner it's power loss and 1500 - 3000 RPM. When richer, it's up to 2500 RPM and, with a lot of throttle, it "backfires" (just like rich exhaust in a hot exhaust system). Otherwise, the stumble has had the same general character from the start: significant missing under load, like when taking off from a stop.

So, what else is it?

Maybe my new used coil is bad (though Carl Leo said it tested good)? Maybe the other one is bad -- I don't think the resistance test is completely reliable. I don't notice much change with operating temperature or length of ride, except it does run great in the first mile before anything shows on the temp gauge.

I so wish I could just put some new coils in it. How long have these been unavailable? Has anyone installed an aftermarket coil -- like maybe http://www.jpcycles.com/product/380-086 or http://www.jpcycles.com/product/381-326?

Or maybe it's some whole nuther thing?

Frustrating.

[Nails]

Nobody uses an aftermarket coil?

[Nails]

Okay, these look like direct bolt-up replacements. I'll give them a try, as soon as I confirm that it really is new.

https://newmotorcycleparts.net/electrical/coils.html "Honda-Kawasaki Type Coil":

This also looks like a bolt-up: http://www.regulatorrectifier.com/catal ... ition-coil

I found this to be interesting reading: http://www.motorcycleproject.com/text/h ... coils.html.

[cranky]

... I"d make SURE I knew where that coil is... you may be back to visit it.... JM2C

[HarryL]

Just a thought, but I noticed in a recent post that you had blanked off the Reed valves. Could this possibly cause an increase in internal engine pressure that may be affecting engine vacuum?

[Nails]

Reed valves

Thanks. But I understand Canadian models came stock this way.

Yesterday, after running a while, it rather suddenly got a lot worse. It was missing, probably on two cylinders (but I couldn't tell with a spit test on the headers), pretty-much all the time below about 3500 RPM. I think a dying coil died.

This morning it started and idled okay. But it's parked until I get some coils to swap in. And I really want to quit screwing around and get some new ones. That NewMotorcycleParts link (above) is a new coil, and it's in stock. $89.40 for two. We'll see.

[Nails]

Okay, I ordered those coils on Thursday, and by Monday noon they are installed.

First off, the L and R coils (stock and otherwise) are entirely interchangeable. The mounts are reversible. The positive (red) wire goes to the front on the left one and the rear for the right one. (Mine had both red wires to the front, but I don't think that really matters very much.) I'll carry one spare coil.

Regarding these new coils, they're very much like the stock ones. The biggest difference is that they say "Made in Taiwan" instead of "Made in Japan". The secondary (spark plug) flanges are larger, but they provide the plasticware to convert the stock wires. Basically a simple bolt-up replacement.

And (drum roll, please) ...

Well, it still has a miss, but a different character: it used to miss pretty bad under a load, but now it misses less and all the time. Cylinder 3 is dead. But it actually does have more power under a load.

That spark plug was shattered -- both top and electrode insulators cracked to hell and gone. I think this happened last week when I decided to park it.

Replaced the plug, and still dead. Swapped the sparkplug wires at the coil, and #3 still dead. Replaced that wire, and still dead. No obvious carbon tracks on the cap or anywhere else.

I'm heading into town for a 3mm allen that'll get to the bottom of carb #3. (I did verify that I didn't confuse "right" and "other right" when fussing with the pilot jets. #3 was where I wanted it to be. But I put all out to 1.75 turns.)

To sum up, I think those new coils fixed one problem; and I would buy them again. Last week's spark plug incident is a new problem, perhaps related to a lean condition. Please don't mention "compression" to me right now.

My multimeter died, so I can't check the oil coil resistance. I'm guessing that 2/3 coil was also impaired (I already replaced 1/4) because I got it home on more than 1 cylinder. I mean, 2/3 were failing intermittently, and then #3 failed completely. The new coils apparently fixed the former. (Now to see how long they last.)

I swear, I've never had a bike so unwilling to run right. (I'm sure I'm back on Mike's "hopeless" list.)

[Nails]

More than a little fuel in the float bowl. Swapped in a different plug cap, but didn't help. What I can see of the piston looks fine. I can't check compression cause I don't have an adapter than small -- will ask of a friend.
At this point, I either have no clue what to do next, or the motor is fried, pending compression check. I'm ready to beat it with big sticks and rocks, 'cept I hate to chip the new paint.

[ekap1200]

More than a little fuel in the float bowl. Swapped in a different plug cap, but didn't help. What I can see of the piston looks fine. I can't check compression cause I don't have an adapter than small -- will ask of a friend.
At this point, I either have no clue what to do next, or the motor is fried, pending compression check. I'm ready to beat it with big sticks and rocks, 'cept I hate to chip the new paint.

Hello from NJ, read the post ( ROADSIDE DIAGNOSTICS ) i THINK IT MAY ALSO APPLY TO YOU. you both seem to have been traveling the same path.....

[Nails]

Yeah, I've been looking at that. But I only have misfire on #3, which is very new. Just a week ago, it missed intermittently under load; but all four cylinders got sizzling hot. With the new coils it runs swell under load, but #3 is cold dead all the time.

I found the #3 plug was busted, but not from impact (insulation badly cracked, the electrode is fine). I did run it lean when screwing with the pilot screw. Not for long, but maybe the plug was also a little defective. Dunno. Could a poor connection between the wire and boot cause plug overheating?

Despite that, I've pretty-much ruled out a spark problem: new plug, changed caps and wires, swapped wires at the coil (#2 runs fine).

I'm very skeptical of a fuel problem. The cylinder is cold-out dead, not just missing. That carb has fuel in the float bowl. I just cleaned/rebuilt the carbs; and they've been doing swell. I have the pilot screws at 1.75 out, which should at least fire.

I still can't check the compression for want of the right adapter. (With the valve covers off, I might be able to do a cold compression check. I'll try tomorrow.) The valve train looks fine, but I haven't turned it over with a wrench. There's sure nothing obvious keeping a valve open. I also borrowed a camera to look in the cylinder.

Don't know what else I can check. Very frustrating.