High altitude issues.

[rdmcguy]

my 2 cents

Living here at altitude 5280 ft. and going to the high country...8-10-12,000 ft.
fairly often I can say that with factory jetting I never have a problem with stumbling/missing or sooty plugs ... A loss of power YES .
.I do have pods and headers on three of my 11's and all run very well from the bottom end to redline ..
Don't know if you run altered jetting or no...dirty air filter ..old plugs ?
Just tossing out the obvious often overlooked...

[BA80]

Cleaned filter before the trip (UNI foam filter), changed to NEW plugs at Brent's place. +1 size on jets, main and pilot.

[motoman]

Out of popcorn., so I'll add something to the fueling side of things to ponder.
Thanks to the spring-loaded float needle springs not all having the same compression rate, static float level settings and actual bowl fuel levels WILL vary between the four carbs. ESPECIALLY if replaced with new ones that are NOT Genuine Mikuni needles(sucks that Mikuni sells needle,seat, etc. as a kit@ almost $40 a pop for the later o-ringed seat carbs). Dealing with that now, having used new K&L float needles. If I gotta chase those running fuel levels to be identical across all four more than a couple more times, them damn things are oughta' there and I'll fine emory LIGHTLY spin the viton 'clean'(old school carb rebuilding trick) for a good seal on the original Mikuni float needles.At least their sealing point spring compression AND the slight compression while running(fuel level pressure up against float) better matches across all four carbs.

[3Phase]

Greg,

Is the 2/3 coil in good shape? If it's getting weak, #3 might be misfiring.

The Wasted Spark coil setup fires one plug positive and one negative but do you remember the old pencil test to check coil polarity? Negative polarity is supposed to be bad because it takes more energy to fire a spark plug and fuel economy and power suffers. If the coil is weak, the positive plug would fire and the negative would misfire.

Use an insulated tool to hold the pencil -- not your fingers and not by the metal band with the eraser in it! Put the graphite tip between the spark plug wire and the spark plug, then watch the direction of the spark flare when the plug is fired to see if the coil polarity is positive or negative when #3 is fired.

Or just switch the stupid coils around and go for a ride to see if #3 starts working and #1 or #4 gathers soot.

.

[BA80]

It was just #3 that was dark, all others looked perfect, tan/black edges. When it was sputtering and misfiring (no power) it seemed like all.

I'm in Oklahoma now and it runs great. A wonderment I say, a wonderment.

[CaptonZap]

You know, judging from the pictures, it looked like classic carb ice weather.

CZ

[BA80]

Temps didn't have anything to do with it, just altitude. Tod's XJ with pods and Johns XS did just fine. It was just my bike.

[CaptonZap]

Geez Greg, you're no fun! We could have argued on for another round about the CV carbs being susceptible to carb icing.
Oh well, back to oil and tire research.

CZ

[3Phase]

Temps didn't have anything to do with it, just altitude. Tod's XJ with pods and Johns XS did just fine. It was just my bike.

So the whole engine was misfiring, or more than just one cylinder, and losing power up in the mountains, not just #3 but it's fine now that you're back down in Oklahoma.

You need to get high. Go back up to the mountains and do all the tests, you can't troubleshoot altitude trouble when you're not high!

.

[rdmcguy]

Getting high?

Hey maybe if you had picked up some legal ""smoke "while you were here
You could indulge in that now and maybe you could just IMAGINE the misfiring
issues in the comfort of your hometown?...lol

[3Phase]

Hey now! It's a legitimate medical requirement with that poor, ailing XS1100!

You'll know it's high enough when the symptoms include the #3 spark plug being not just brown, but chocolate brownie colored brown with ....

.

[BA80]

Hey maybe if you had picked up some legal ""smoke "while you were here
You could indulge in that now and maybe you could just IMAGINE the misfiring
issues in the comfort of your hometown?...lol

They were selling that stuff on every street corner. Some really ambitious looking characters too.

[BA80]

So the whole engine was misfiring, or more than just one cylinder, and losing power up in the mountains, not just #3 but it's fine now that you're back down in Oklahoma.

You need to get high. Go back up to the mountains and do all the tests, you can't troubleshoot altitude trouble when you're not high!

.

Yeah, it was like it was running out of gas when I twisted the throttle past about halfway.

I was hoping one of these high geniuses here would know the answer. I'm not certain if it was electrical or fuel related. I'm pretty sure that #3 cylinder has a leaky valve seal, it was black at this elevation too. I just swap 3 and 4 around every now and then to keep it cleaned up. Every now and then it'll smoke pretty good when I start it up.

[3Phase]

I was going to ask if any of the valve seals were getting toasty and I thought, "Nah, he'd say something." That's probably the plug color then and more of a side issue than the missing upper half of the throttle range.

Are you sure the fuel tank filters/screens are good, not full of junk and the fuel lines aren't kinked or flattened out from heat/age.

How about those tiny little filter screens on the float valves, are those good or did they get bumped over the back of the bench and never make it back into the carbs?

Did the misfire/bogging kind of go away if you 'worked' the throttle or did it just start to suck wind anywhere over half throttle until you backed off?

Not enough fuel and not enough air would kill off the top end. You'd be totally overcarbureted with only enough fuel to feed an XS550 or XS275 if they made such a critter. Now that you're back down in the lowlands it's not a catastrophically-lean mix, it's a merely-lean mix that runs faster than an ammoniated feline.

.

[BA80]

It just sucked over half throttle.

Here's what the plugs look like after 2000 miles or so. Put them in new at Brant's place. Went over 2 more passes over 10,000 ft and it always did the same thing until I dropped down below about 8000 ft.