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When I am going up a hill and giving it throttle with a load on the engine I feel it stumble once in awhile. The carbs were rebuilt replacing everything inside that could be replaced. Both petcocks are on when this happens. I am leaning toward float levels, any other ideas as to cause?

Leads and plugs are relatively new, about 1000 miles on them. I only noticed it first when I am on a road in the mountains and I am accelerating up the hill, about 6000 feet or so. Did notice some of the same behavior today when I was on the freeway accelerating around 80. I usually don't ride on the freeway so this is the first time.

Check and/or replace the short wire between the two coils. Friend on another forum had similar issues and it was that wire making intermittent contact. I'm thinking the added vibration of acceleration was enough to make it happen.

Are you running points or electronic ignition? Before I got new coils I had to file the points every few thousand to fix intermittent missing.

Since yours seems to be happening with very high fuel demand it may be due to limited fuel flow. Both petcocks open?

Charlie, I am running the stock ignition system w/points. I reviewed Duane's information on fuel flow, so I will check that out tomorrow. I have 100cc in 12-15 seconds as the mark to look for. When I first got the bike I changed the tubes and screens in the tank, so depending the lining flaking that may be Ok. Everything in the fuel system was changed, floats, all jets, needles diaphragm. I do have springs over the diaphragm.
I have a mail box in Virginia City, so when I climb that road I am usually pulling it in 4th gear, speed varies between 55-70 depending which section I am on. It doesn't do it with a lot of repetition, but you feel it as an occasional event, usually when a strong load is placed on it.
Both petcocks are open, that was the first thing I tried when this started.

Seems like you have the fuel supply covered.

The reason I asked about ignition is that I had stumbling/missing that would usually start at high revs then gradually get worse and occur at lower revs. When it was happening in top gear at usual touring speed the irritation factor would kick in and I would have to find a place to stop and deal with it. Out of the sun or rain and comfortable enough to lie on the ground was the requirement. I would file the points, check the gap and static timing, button up and hit the road again.

Along the way I bought an electronic ignition - Omega, crank mounted - which worked well but failed eventually and I went back to points with the same irritating bloody problem. Then I lashed out for a pair of new Bosch coils and haven't been troubled since. I'm telling this story just in case you still have the original coils. New coils are full of fat blue sparks and are less inclined to burn points.

This may not be your problem of course, but it did me good to relate the story.

Never thought about the coils. I figure they are original. This bike sports a EU vin number so I don't know where it was delivered. The clock shows 11100, foot peg rubbers says it's possibly been around once. So I don't know if the original was in KPH and if this is a MPH replacement.
I hope to get to it today, my Outback acted up with the sound of the starter solenoid rattling and not having enough oomph to engage. If I am lucky it's new battery time, if not, new starter time, can't complain 257K on the original.

Hope to start on bike today depending....got a big list to go through.

Fixed Outback, just needed some PM and cleaning and tightening of terminals on battery.

First test on bike, fuel flow: left side 235 ML in 15 seconds, Right side 233 Ml in 15 seconds. OOps that was on reserve, not going through screen, Now left is 196 ML in 15 seconds, Right 193 Ml in 15 seconds.
Did see some black specs of stuff in fuel, not a lot but some.

Coils look like they are original, checked center electrodes inside the coils, nice and clean can see brass. Plugs are dark brown on left side, darker brown on right side. My estimation is that we are a little fat on mixture, could be weak spark.

Guess I will see who has new coils since I am in upgrade mood.