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Discussion Starter · #1 ·
Here is the scenerio, I have a 1980 Deluxe bike with the regular tank and gravity feed petcock and the stock carbs have the fuel inlet on the left side right below my petcock. I bought some different carbs and they have the fuel inlet in between the carbs. Unfortunately, the fuel inlet is almost exactly the same height as the petcock, thus hindering the gravity fed fuel flow. If I raise the rear of the tank, the fuel will flow with no problem at all. I was thinking of 3 possible fixes to the problem.



1. Cut down the center fuel inlet to the "new" carbs as low as possible and see if I can get the fuel flow that way.



2. Try and find a vaccuum petcock and see if they are any different and will flow fuel better.



3. Buy a freshly rebuilt set from Larry and hopefully get the left side fuel inlet from him.



Any thoughts or suggestions would be greatly appreciated!!!
 

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a vacuum petcock will not solve your prob..it only changes the way it turns on/off..

as long as your fuel supply is higher then the carb's ,it should flow.

I am leaning toward a "kinked line" to the carb's.

or the liner of the fuel line has come loose .( ethanol gas does this a lot)

try a new fuel line , and make it a lazy of a bend to the carbs as possible ( i/e no sharp bends)
 

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Discussion Starter · #3 ·
a vacuum petcock will not solve your prob..it only changes the way it turns on/off..

as long as your fuel supply is higher then the carb's ,it should flow.

I am leaning toward a "kinked line" to the carb's.

or the liner of the fuel line has come loose .( ethanol gas does this a lot)

try a new fuel line , and make it a lazy of a bend to the carbs as possible ( i/e no sharp bends)


It's not kinked and I have put several new lines on it to try it in different routes to the carb. The only thing that seems to matter is the vertical distance between the petcock and fuel inlet tube.......
 

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The fuel level in the tank is what controls the gravity feed. Any liquid will find its own level.



The fuel inlet could be above the petcock and the fuel would still flow as long as the level of the fuel in the tank was higher than the inlet on the carbs. There has to be something blocking the flow (kink in the hose, blockage, etc) or not enough fuel in the tank. A higher level of fuel in the tank will provide more pressure, therefore faster flow.



Did you put a minimum amount of fuel in until you checked everything? Try adding more fuel.
 

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Discussion Starter · #5 ·
The fuel level in the tank is what controls the gravity feed. Any liquid will find its own level.



The fuel inlet could be above the petcock and the fuel would still flow as long as the level of the fuel in the tank was higher than the inlet on the carbs. There has to be something blocking the flow (kink in the hose, blockage, etc) or not enough fuel in the tank. A higher level of fuel in the tank will provide more pressure, therefore faster flow.



Did you put a minimum amount of fuel in until you checked everything? Try adding more fuel.




Tank is full to the top. I can't say exactly why it is doing this, but it is definitely happening. I agree with you completely, but this setup seems to defy the laws of physics. I'm pretty much stumped. Like I said though, if I raise the rear of the tank up higher, then the fuel flows like normal. I know this sounds like a kinked or obstructed hose, but I've gone though several feet of new hose trying new configurations both with and without the inline filter.
 

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Discussion Starter · #6 ·
I also thought that the tank vent might be plugged, so I opened the gas cap, but no change....



I opened the float bowl drains to see if there was a vapor lock type situation going on, but again, no change....





It flows minimally (enough to idle the bike) but no more. It was perfectly fine with the other carb setup but unfortunately the other carbs may be beyond repair.
 

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Discussion Starter · #8 ·
Have you gone through the petcock? Sounds to me this is where your problem is.


I took it off and blew shop air through it. It seemed to blow through freely. Do you think that I need to physically get something in there and clean it?
 

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Something in the tank that blocks the outlet and moves out of the way when you lift the tank??



Float adjustment?



( I'm just typing ideas as I get them.)
 

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Had you checked the flow of fuel from the line removed from the carb's? If fuel dumps freely this way then I'd think there was a restriction between the carb inlet and crossover tube.
 

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Discussion Starter · #12 ·
Something in the tank that blocks the outlet and moves out of the way when you lift the tank??



Float adjustment?



( I'm just typing ideas as I get them.)


All ideas are more than welcome and greatly appreciated! I am going to tear into it tonight and check it all out. I figure that all the guru's around here would have some ideas that I never thought of. I will check out each and every one of these ( and any more that get suggested) tonight and report back my findings tomorrow.
 

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Discussion Starter · #13 ·
Had you checked the flow of fuel from the line removed from the carb's? If fuel dumps freely this way then I'd think there was a restriction between the carb inlet and crossover tube.


Good thinking! I will check this out tonight as well!!
 

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This might sound stupid, but it is worth a thought nonetheless... Is the fuel filter installed correctly? Flow direction can make a difference on the filter.



The problem will be something simple. Personally I doubt it is the tank height.
 

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Discussion Starter · #15 ·
Well, I checked the line flow with the line disconnected and it flowed, but slowly. At this point, I took the petcock out and cleaned it thoroughly. I replaced the fuel line once again and pulled the carbs off. I checked and re-cleaned the needle and seat assemblies in the carbs and blew shop air through the fuel inlet. Reassembled everything and voila! All fixed. I am not 100% sure where the problem was, but I can say that there was junk in both teh petcock and needle valves. So, no there was no reason why tilting the tank should have made a difference. Thanks eveyone for your help!!!!!
 
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