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Got a modest fuel starvation thing going on.

I've checked the petcocks, float levels, cleared the mainjets. I've not absolutely confirmed that it's a cap venting problem, but in the event I do confirm it, what's the fix? I see that rivet in the middle, I'd hate to think I've got to drill that out.

Melville, why do you think it's fuel starvation? Is it losing power at sustained full throttle? If so, likely float level is set too low or perhaps the slide needle could be raised a notch? I think the cap can vent through the rivet hole, but there is another tiny hole in the raised lip of the round plate that holds the cork gasket. If you want to replace the cork disc just pry the old one out, you can then reuse the rivet and special washer.

Tim Shepherd wrote:Melville, why do you think it's fuel starvation? Is it losing power at sustained full throttle? If so, likely float level is set too low or perhaps the slide needle could be raised a notch? I think the cap can vent through the rivet hole, but there is another tiny hole in the raised lip of the round plate that holds the cork gasket. If you want to replace the cork disc just pry the old one out, you can then reuse the rivet and special washer.

I might add to Tims post, if you haven't yet, when the bike stumbles reach down and open the cap and see if the problem goes away,

Also, when the bike is doing is 'starvation thing', pull the choke on for a second or two. If the bike returns to normal operation, it's a fuel thing.

Well, it gives me the "go to reserve already" stumble about 3 to 4 minutes into a high-load situation. Just East of me is a mountain pass that comes in two steps--first step is less than two miles of 6% grade, and I'm not troubled by the stumble on that one. The second step is 6 miles of 6% grade, and it will generally stumble about 3 to 5 miles into it. 4th gear, 5K rpm.

Reducing the load slightly helps for a bit, but of course this happens when I'm trying to get an uphill pass in before the passing lane runs out and the would be passee slows down in the forthcoming twisties. I'd like to be finishing that pass.

I suspect the cap, but will check other stuff as well. It may be a few weeks before I can get out there to test.

Sounds much mo' like a tad too low float level.
Classic symptoms.

A holed diaphragm will give those symptoms as soon as you open the throttle.

The fact that backing off the throttle eases the symptoms suggests low float.

It's quite possible the gas cap is the culprit and Richard's suggestion will tell you immediately. Well, almost immediately.

Got out on it, and it's not the cap. It starved whether cap open or not. Quite the thing, opening the cap whilst all leaned over at (modestly illegal speed) in fourth gear.

This weekend, I'll be dicking with the float levels and making sure I got the needles in the right (and same on both sides) spot. I'll also be quantifying flow through the taps more precisely than "same on each side."

melville wrote:
This weekend, I'll be dicking with the float levels

That's not how I'd adjust my float level, but if that's how you like to do it, okay.

Major Softie wrote:

melville wrote:
This weekend, I'll be dicking with the float levels

That's not how I'd adjust my float level, but if that's how you like to do it, okay.

Might want to check the diaphragms while you're in there. Flowers and a bottle of wine should get her in the mood!

Tim Shepherd wrote: Flowers and a bottle of wine should get her in the mood!

Not if he goes ahead with the float thing......