Fuel flow mystery.

[excess.11]

Brian.......was the fuel prob there before you used the carb clean? What you have done is simply bypassed the problem which is fine in the short term......but maybe you should investigate more what is causing the problem . I d swap diaphrams in the fuel taps from one side to the other and see if one has nt gone hard or otherwise and the prob shifts to carbs 1 & 2 .Check that compression  hasn t been affected after using the solvent cleaner.You could simply use longer vac hoses and cross them over to determine if one has a better vac than the other....i m thinking this in conjuction with a full tank , compared to an almost empty tank , has a greater pressure on the fuel tap diaphram and assists with weight and gravity in keeping the fuel tap diaphram open.When you change to reserve your allowing the weight of fuel to again assist in keeping the fuel tap diaphram open.I see 2 areas being bypassed with the new hose set up.The diaphram in the fuel tap with the weight of fuel and gravity assisting  and the vac pressure scenario  .

DITTO....................even if i do say so myself.....

[Eveready1100]

Ok brian, I'll buy that. It had me really scratching my head, but with that bit of logic, it all makes sense now. Thanks mate. That's anotherie I owe you.

[melbxs]

There's about an inch of fuel above the tap on the normal setting. The vaccum is enough to hold that up. When you switch to reserve there is a much greater volume (weight) of fuel over the tap and the extra pressure is enough to beat the vacuum for a while longer.

[Eveready1100]

Just recently, my bike's been behaving strangely when the fuel level gets down a bit, just like it's running out of fuel. Quite similar to the symptoms described by Bryan in this thread - Click
It first became apparent on the recent " not the Laverda Bike show run" but didn't really take too much notice of it back then. More lately, I've been able to notice it more and on my latest trip to Brisvegas with the trailer loaded up to the hilt with all my power tools & gear for a Backyard blitz at my sons place, I started to put two & two together.
Here's the way it happens - Fill with fuel, ride down the highway 140 k's or so, bike starts to blubber & miss. Switch to reserve, motor starts to run clean again, then look for servo. Fill up again but it only takes about 10 - 11 litres to fill. This is the bit I was failing to notice before.
The last time it happened, I'd just got back to Childers from work in Bundaberg. Only about 120 klms, but I'd been playing a bit and I still had the trailer on sans tools. Switch to reserve and as I'm only a few Klms from home, I went there instead of diving into the nearest servo for a refill.
When i pulled up and stopped the motor, I heard a high pitched whistle coming from my fuel cap. Aha! A blocked cap vent was causing starvation as the fuel level dropped. I've wheeled the bike into the garage to surgically remove whatever is blocking the vent and hopefully cure this symptom.
But now, I've really got a puzzler for anyone who can help me on this.
Why would switching the fuel taps to reserve get the motor running smoothly again when it was the fuel cap vent blockage causing the issue, not the fuel level?