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Old 08-30-2011, 05:46 PM   #87
motodavid2000 OP
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Joined: Jun 2009
Location: USA - Florida and Ohio
Oddometer: 228
Head Pressure of Fuel

Originally Posted by TRAVELGUY View Post
Dave have I been operating under a miss assumption? I have always thought that atmospheric pressure pushed the fuel out of the tank ( Tank Vent ) and with your loop in your fuel line you would only have a very small amount of fuel left in the line after the tank runs dry. Am I missing something?

Great bike build. Was worth the two year wait to see.

Tom -

Good to hear from you. Hope that you are enjoying Costa Rica.

No, you are not under any misconception. From my classes back at Purdue University so many years ago, the head pressure of the fuel is the delta in fluid levels. The issue becomes flow rates to the carb from the tank, combined with dropping fluid (fuel) levels and reduced head pressure.

Without spending time calculating some theoretical point, I am sure that the carb can be "starved" of fuel when a combination of low head pressure (low fuel levels) and high flow rate (fuel draw) causes insufficient fuel delivery to the carb based upon engine needs. I think that this would be experienced at very low fuel levels and higher loads & revs on the engine; perhaps exagerated with high altitude operation.

My general take is that the carb should not be starved of fuel when it is at least 25% or more full of fuel, operating at any reasonable engine load.

My fuel line loop below the carb inlet would cause a loss of a small amount of fuel not being available for the engine, and possibly an air bubble to form. This would be an extreme case, and the engine would / may be starved of fuel before that time with low head pressure and higher engine loads.

I don't think that the engine would starve at idle until the fuel reached the level of the fuel tank petcock intake.

Getting ready to make a few more mods to the windscreen and instrument panel supports. Will post some pics when the work is done.

Also, still resolving fork stroke / tire bottoming probabilities - have not disassembled the forks yet and want to ride it first. If I need to change springs, I will check fork stroke / bottoming stroke and also change springs at the same time.

Take care - Dave
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