Plugged main jets? Do you have inline fuel filters? Could these be restricting fuel flow?

I had a similar problem at around 80 mph about 6 years ago. I bent the floats to where they should be and that solved the problem. Maybe take a look at where your floats are sitting/how much fuel sits in the bowl when you remove it (of course the bike would need to be on the center stand). I hope this helps!

Thanks so much. I will break my carbs down and combine both the suggestions I have received so far. Clogged ports and misaligned floats. Both are very possible from that putz that rebuilt both my carbs.................ME!!!!

Wm's suggestion about float height is a good one. There should be a specified height in the manual. Do also check for any restrictions on fuel flow like clogged filters on your fuel taps inside the tank, crimped crossover pipe or clogged inline fuel filters if you are running those. I think I would start by flushing out the tank and go from there. It sounds like you don't have sufficient fuel flow at more open throttle settings so anything restricting fuel flow along the path may be the culprit. Please let us know what you find out!

Tobin

If you are in the USA, then the Number 1 suspect is ethanol fuel.

Set Up
But first you'll need to do some initial work to make sure we are chasing the correct demon. Don't worry, it's VERY inexpensive. But also VERY necessary...
• Strobe time your engine at VERY HIGH rpm using the "F" mark. Your install manual probably gives an RPM range, so follow that. If not use 5000 RPM.

• Install new metal core plug wires along with new NGK 5K Ohm resister plug caps.

• Install 2 new NGK BP7ES plugs with lubrication on the threads.

• Install a new air filter.

Carbs
I agree it sounds exactly like a lean condition. That can be caused by many, many things... air leak, low float level, torn diaphragm, or varnish-coated jets. You gotta check them all...
• Remove the carbs from the bike.

• Withdraw the slide and inspect the diaphragm for holes. Inspect the needles for any sign of varnish, pitting, wear or corrosion. They must be perfectly smooth under magnification. Not all the older needles are brass, so they may appear to be Parkerized. If there is any doubt about their surface quality, then order a new set. Install those with the exact same exposed length, which should be identical for both sides.

• Check the float level with the carb body so that the gasket surface is in the vertical position, pivot at top. Allow only gravity to push on the spring loaded float needle.

• Replace any jets that have a brownish varnish appearance. Replace the 2 main jets regardless.

• Reassemble and reinstall the carbs with 2 new intake rubber hoses.

Treatment
Buy a bottle of StarTron fuel treatment and start adding 1oz to every tank full of High Test fuel you buy, until the bottle is used up. Home Depot, boating supply stores, and lawn and garden supply stores sell this stuff. It's easy to find and nothing else works as well.

Somewhere in there, things are going to get better.

Thanks so much. I have my carbs next to my desk ready to pull apart. You folks out there in airhead land always step up to help. It is much appreciated. I will let you all know the conclusion............
Best to you, Cliff

Apologies. Just remembered some other items you'll want to check....

All the focus so far has been on not enough fuel leaving the carb headed for the engine. But if the carbs don't receive enough fuel, then you'd have the exact same symptoms, but for an entirely different reason.

• A R75/6 that had sat for an extended period had fuel delivery issues. In the OFF positions, the fuel supply was indeed stopped. However, in the ON positions, the petcocks would only dribble fuel. The problem was the internal packing had gotten twisted around. If you'll place a small cup (like a spray paint cap) under each petcock, each individual petcock should be able to deliver fuel at a rate of approximately 1 Tablespoon per second. If not, check the screens and/or replace the internal packing.

• Another issue was associated with the use of American 5/16" ID fuel line. Due to its larger OD, this size line can get crushed in the cross-over section, where it passes through the air filter housing. If you run with only a single petcock ON, then the opposite carb may be starved for fuel.

5/16" fuel line works very nicely on Airheads, except on the cross-over. If that's the only fuel hose you can get, then simply turn the T-connectors to point rearward, and run the cross-over external to the engine, around the rear of the air filter housing. It will take considerably more hose, but it works. There is no need to block either hole left in the air filter cover when doing this.

Working out all the kinks after an Airhead sits can seem daunting, but the rewards are worth it !

Hope this helps.

So . . . what did you find? I am curious if you've had a chance to diagnose and discover. I recently cleaned my fuel tank, and I was amazed at how much garbage accumulated in there, so, as posted above by others, there could be all sorts of reasons.

I will post the conclusion when I have it. So far I have bought the Startron. I have received a new set of floats. I did my carbs only two seasons ago completely. I am also going to remove the fuel screens I installed on the fuel lines. I ordered new fuel lines as well. I have a friend that permits me to use his equipment and he is a Harley mechanic. I will double check the high rpm, timing this coming weekend as well. I switched to an electronic ignition before this season, and that has been terrific, but I had this issue prior to the switch from points. BTW, I removed the petcocks two weeks ago and you are so correct, they do accumulate a ton of junk, with screens and all.
Thanks for the follow up, I will know much more next week. The flow issue seems to me to be the issue. I just need to find the bottleneck at this point.
Best to you folks, Cliff

I will post the conclusion when I have it. So far I have bought the Startron. I have received a new set of floats. I did my carbs only two seasons ago completely.

Cliff -
Just reviewing your post to see if there were any updates. Hoping all is well.

A comment, if you don't mind, about the highlighted statement above.... If you ride in USA and Canada, then that one sentence means absolutely zero. Here's the root cause: You're still thinking about gasoline in terms of the fuel we had back in the 1970's and 80's. The fuel we grew up with is as different from today's fuel is as a dog is from a cow. Both liquids are called "gasoline" and both go into the fuel tank. That's about it !!

The addition of ethanol (which attracts and absorbs water) means that if fuel sits in the float bowl for as little time as 2 months, then bad things start to happen. So in the intervening "two seasons", if the bike was parked for any significant time, then all bets are off on ANY PART of the fuel delivery system that was submerged in the ethanol fuel.

People don't think about fuel this way because they don't have any trouble with their car. But cars have a fuel injection system that forces fuel into the intake tract. A carburetor can't force anything; it works solely on vacuum. So it only takes a minuscule blockage to reek havoc on our vintage fuel systems.

Hope this points the way to some improved storage procedures.
All the best.

Men, I can''t tell you how much I appreciate the input. I am working my way thru the repair. I am on my second tank of additive. I have the float on the bench. Fuel filters are a memory. I run the carbs dry any time I am putting the bike up for even a few weeks. I am thinking the carbs are my last factor. I am doing the easy ones first. I am more than optimistic I am on the road to recovery.
I have been lucky enough to hook up with a Harley mechanic that works on his own, where I apprentice almost every weekend. Darn, at 62 I am back in vocational school! I couldn't be having more fun. The 5 month old grandkid complicates things but the last year or so has been an excellent automotive stretch.

Wobbly makes some good points about modern fuels and ethanol. I try to use ethanol-free supreme fuel in all my bikes and small engines. I also keep Stabil in everything and try to turn the fuel over (ie. drain it out and run it in a car) at least every year for every machine. Knock on wood I have not had any problems with gummed up carbs yet! I would recommend avoiding fuel containing ethanol if you can, especially if it being stored for extended periods.This can be difficult when you are on the road but is probably not that much of an issue when fuel is flowing through the bike. I also try to empty float bowls after every season but often don't get to it. So far, no problems.

Good practices all, TP. Thanks for speaking up.
CTC

Wobbly makes some good points about modern fuels and ethanol. I try to use ethanol-free supreme fuel in all my bikes and small engines. I also keep Stabil in everything....

I'm no Chemical Engineer, but if my information is correct, then you may not need Stabil when you use ethanol-free fuels. The main thing that Stabil does is keep the gasoline and the ethanol in solution. Without it, the 2 liquids start to separate over time, and that's when the ethanol (in its purer state) starts to do a number on your carbs. And additionally, your engine can't run on high percentages of ethanol, which is why the pugs end up fouled.

That's one reason you don't want to buy fuel from an out-of-the-way gas station. The same separation takes place in the storage tanks. So it's possible to get a big slug of ethanol instead of the low percentage mixture the EPA dreamed of. Of course when this happens, you don't get to send the repair bill to the EPA !