High altitude issues.

[jetmechmarty]

Exactly.

But he's running the stock airbox; don't remember if he's got stock exhaust or aftermarket. With the jetting he's running it should be rich but the plugs are lean clean.

.

Agreed. I'll shut up now.

[3Phase]

Nah, don't do that, try and figure out why it's running lean when it's jetted rich. I'm baffled but that's normal for me, you're one of the sane(er) ones so what do you think is going on?

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[Bonz]

Any way there could be a minor air leak on #4 if the carbs are otherwise in good repair?

If the bike runs well at lower elevation, it's not a major deal whatever it is, but either #4 is getting incrementally less fuel or it's getting incrementally more air as it sits right now.

High altitude stuff was the jetting, no question.

[rdmcguy]

2 cents more from me

I agree with Bonz...jetting !!!
As a poor youngster we would either put the choke on and see if there was any improvement ...or remove the air filter (briefly) to help determine which to go jetting wise ...primitive but most times effective ..

[jetmechmarty]

I thought the jetting was fat? Bonz said his works one size smaller than stock on the mains. I have no reason to doubt him, so Greg must be drawing more air someplace, assuming all else is as it should be.

[motoman]

......and missing voltage 'smoke' is just compounding the issue.....still gonna stick with that until HONEST volt and coil ohm numbers are first reported back.

[Bonz]

Yes, I think he was fat at altitude, but getting away with the over-jetting on thick air in lower elevations. My comparison is relative to what I am running at elevation, he is two sizes larger on mains relatively speaking, and one size up on pilots which is (believe it or not) adding to the richness even more at elevation once the butterflies open. Kind of a double whammy.

Motoman was doing this goofy pilot setting method last summer and was way rich at the rally and gave me carbon monoxide poisoning when following him up Pikes Peak. We started backing down the adjustment to lean it up a bit and were on the right track before he left for home.

The fact one cylinder is runnng whiter in plug color isn't as much of a concern simply because it has probably been doing it for a long time as witnessed by it running well before and continuing to do so now that he is back at lower elevation. If everything else checks out, then ride the wheels off it!

[BA80]

OK, I don't think it's a rich issue because the plugs don't show a rich condition. I think it was a spark issue brought on by the altitude. John's electronic lighter wouldn't light on top of the pass either. He tried making some coffee but we couldn't get the lighter to light his little survival stove. I have 1 size over mains at a 140 and pilots are 1 size over at a 45.


I found that the breaker plate was sticking but I don't think that would cause the misfire I was getting on all cylinders.

I took the coils off and checked them. They ohmed on the primary at 1.9 - 2.0 which I thought was a little high but a quick check of several others in the garage revealed that was pretty normal. Secondary checked out good too.

I went ahead and put some 3 ohm coils off of an 81 on there and eliminated the ballast resistor. It seems to have it's old fire back now. It'll pull the front wheel for a second shifting through the first 3 gears.

Bad ballast resistor maybe? Don't know how to test that.

To answer the question of the air box, yes, I have a stock air box. everything else is listed in my signature.

[3Phase]

D'oh! Mac 4 into 2 exhaust Sorry about that, Greg!

"I wear my suuunglasses at night
So I can't, so I can't read the screen ...."

.

[Bonz]

The lighter wouldn't light because of the thin air, altitude doesn't do anything to an electronic spark firing, just won't ignite whatever it is trying to ignite because of low O2. You have the fuel and spark, but the O2 is left behind in Oklahoma...

Bic lighters with good old fashioned flint spark are buggers to light at elevation when backpacking, especially if there is any moisture in the air (humidity).

Glad you found the issue by going to different coils, weak spark would make an already hard to light mixture (rich mixture) not want to light even more.

[BA80]

http://papers.sae.org/670147/

[BA80]

Tulsa is at 722ft.............

[3Phase]

Thanks, Greg! That looks like a good paper but I'll have to settle for the abstract.

.

[BA80]

A quick search found that the other day. This is what caught my attention.....

flashover voltages decrease at higher altitudes

[BA80]

The lighter wouldn't light because of the thin air

Fire won't burn at that altitude? Pretty sure Smokey The Bear will disagree.

Tod's and JW's bikes ran fine. JW's Venturer....no ballast resistor. Tod's XJ......no ballast resistor. Then there's Bob's Concours, the fuel injected electronically controlled robot bike.....no problems at all. But it did get dirty.

I could be wrong but it seems there is a pattern forming here.