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OK I have to respond to the wheezing groaning fuel tank deal.
All fuel tanks on carbureted bikes have to vent to atmosphere to allow gravity flow of fuel to keep up with fuel needed to make power. More power more fuel, simple.
A restricted vent will slow fuel delivery to a threshold of inadequate fuel flow into the carbs, resulting in a stumble or stall.
Opening the fuel cap corrects the imbalance and power is restored.Can happen to any fuel system, car truck plane boat, even fuel injected.
Atmospheric pressure in the fuel tank is required for adequate gravity fuel delivery. Less than atmospheric pressure in the tank means the vented carb bowl has enough atmospheric pressure to stop the fuel flow.
I can't imagine a carbed engine using gravity flow would ever whistle through the vent tube or plumbing. The thing would cease to run from lack of fuel before a whistle was evident.
Now a strong fuel pump might draw enough fuel out of the tank and cause an audible whistle or some such sound before the engine stalled, if the vent was pinched to extreme, and modern bikes have fuel pumps so it could happen, but today we are talking gravity fed carbs.
So here is where I begin..you need a lot of pressure differential to get an audible whistle.
That could come from the canister, like on the pre-gen carbed ninja 250 in the pics above.
I notice that a lot of you guys are in California and so your bikes have emission components that other states didn't have until now. My current project 2008 250 has a lot fewer emission parts and no canister, you knew that already.
However charcoal canisters exist on most all vehicles in the USA since the 1970's, and every one of them has plumbing attached to the induction system. You knew that also.
So a 1976 vette came in to my shop years ago with a collapsed fuel tank. When you opened the fuel filler door the fuel cap was about six inches below the door.
The tank was collapsed by a vacuum leak at the switching diaphragm on the canister and the vent hose was capped. Had the gas cap been vented there might have been a whistle or groan sound as pressure tried to equalize, but the cap was not vented and neither was the tank so it freaking collapsed.
The car drove in with the complaint about the fuel fill, not a stall or performance issue.
It was carbureted and a stall was eminent from lack of fuel, or had the tank been full of fuel the engine would have flooded and stalled, but my point is whistling fuel tanks and or stalling motors may involve more than a restricted vent. I can also believe that a rapid change in temperature of the atmosphere inside a fuel tank with a canister, that is open to the induction system during purge ,could reduce gravity flow to carbs, thus a stall,or stumble.
SuspectPage 3 needs qualified diagnostic help before his carbs come off.
If inadequate fuel delivery is not the issue, or weak spark, or chafed wire etc. is not evident and propane enrichment proves the mixture is leaned out, get a qualified carb man on the job.
The end
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