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Discussion Starter #1 (Edited)
2001 Thunderbird, about 17,500 miles, Mikuni carbs, all stock. Runs great although it is sometimes difficult to start when cold. My problem is that the carbs run dry even when the petcock is on reserve, the tank is full and the fuel tank cap is off. I removed the petcock and disassembled it, found nothing wrong. Reinstalled petcock, filled tank and turned petcock to 'on' position. Fuel just dribbles thru the clear fuel line until carbs are full and then stops running when the fuel line is about half way full. I checked the petcock standpipe screens when I had it apart, even sprayed carb cleaner thru them so thats not it. As I said, the bike runs fine, pulls hard to redline and idles smooth until it randomly runs out of gas. Once the fuel line fills again all is good. I looked inside the tank as well as I could and found nothing floating around. I looked from the filler and thru the petcock hole in the bottom of the tank. Breather tubes on the carbs are clear as well. I am stumped. Anyone have any ideas? Thanks
Edit to add that the float levels are set at 15mm.
Edit #2, using 5/16 inch ID clear fuel hose, single hose feed to carbs, no fuel filter.
 

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Are you saying that if you take the hose off the carb and let it hang, and open the petcock, fuel just dribbles out? If so, there aren't many places to look. You should see about 8 gallons per hour that way, or, if you get a pint in less than 60 seconds you're doing fine.
 

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We have witnessed some folks (I had a friend locally with this issue as well) having this problem in the past, turns out the majority of the time there is fine particles from the liner sloughing off and clogging the fuel screen. The particles are tough to see and the screen(s) will look fine.

What seems strange is you have the problem on reserve, I’m assuming there is no screen on reserve?

Have you removed the petcock, disassembled and cleaned it?
 

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Discussion Starter #4
WSC I have not tried that but I will. Doesn't seem likely to me that the problem is in the petcock since I have removed cleaned and reassembled it just last week but I suppose anything is possible.

BRG I did remove the petcock. Disassembled and cleaned screens. No change. The issue presents in both positions, not just on reserve.
Thanks
 

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Is the fuel tank full? Or is there quite a bit less than full? Have you measured how much fuel flow it has in a minute like WSC stated? I suppose you could have a vent issue in the fuel cap or the tip over valve located at the left rear of the fuel tank, if there is still one installed.
 

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My problem is that the carbs run dry even when the petcock is on reserve, the tank is full and the fuel tank cap is off.
That would seem to indicate the petcock is not delivering enough fuel to the fuel line.
I removed the petcock and disassembled it, found nothing wrong. Reinstalled petcock, filled tank and turned petcock to 'on' position. Fuel just dribbles thru the clear fuel line until carbs are full and then stops running when the fuel line is about half way full.
Have you checked the "duck bill" filter? If the fuel cannot get into the manifold on the carbs it will not flow down the line. If you do the test and get good flow with the line off the carbs, then there must be a blockage in the carb rack itself.
 

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Discussion Starter #7
I pulled the tank and petcock today. Pryed the filter screens off and rinsed them from the inside with carb cleaner. The standpipes were clear. Reassembled and reinstalled the petcock. Fuel flow checked good. Disassembled the gas cap and gave it a good cleaning just for good measure. When last I had the carbs off I had removed the duckbill filter so it can't be that. I reinstalled the tank and when I turned on the fuel it appeared to flow forcefully but then stopped before completely filling the fuel line. The bubble just will not go away and I am still stumped.
 

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The bubble is not your problem. If you want to get rid of it, take the line off the carbs, lift the end of it up above the petcock, and open the valve to fill the line. Then put your finger over the end and reattach it to the carbs. It may just come back, though.

Did you do the flow test?

If it just randomly runs out of gas, especially with partial tank after riding for a while, Check the tip over valve. Make sure it isn't stuck shut, and make sure it is oriented right end up. It should open right side up and close upside down (then reopen if you flip it over!)
 

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Discussion Starter #10
The tipover valve is missing so it can't be that. Before I replaced the tank yesterday I placed the tank on the bike and directed the hose into a pan. I then opened the petcock to both positions and it flowed well, no problems there.
The vent lines are clear so that isn't it.
I guess I'll just have to live with it :(
 
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