How critical is fuel tank level in relation to carb?
11-12-2014, 05:25 AM
#76
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I have spent the past several minutes reading thru some of the post here and they are very informative, but not much for the reverse problem (tank lower than recommended (upright engine)). I am wondering if anyone has ever put out a book to cover topics such as this including best ways and locations of the fuel line run thru the firewall, linkage methods, etc.
11-15-2014, 11:29 AM
#77
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Hey, guys, just a couple observations here. As for siphoning, wouldn't a loop in the line above the tank stop the siphoning? And I have read several posts here that hint that muffler pressure forces fuel into the engine, If that were true, engines would not run without muffler pressure. They will. Isn't it more the vacuum from the down stroke of the piston that draws fuel into the engine?
11-15-2014, 06:00 PM
#78
Two stroke glow engines have always depended for fuel delivery upon anywhere from only carb suction to a combination of both suction and muffler pressure and to the point where the engine will not run properly with the muffler pressure absent.
Now what makes the difference is the venturi size and choke used. In years past when generally mufflers were not used and venturi suction was the only way to deliver the fuel, the venturi size and choke had to be kept to a minimum to be able to draw sufficient fuel. In later years when mufflers became common place, suddenly we now had a very simple way to boost fuel delivery. And with this the realization that we now could use a venturi of much larger area to boost power and this was a substancial boost at that. Of course the down side is the sudden loss of muffler pressure (pressure line popping off or a muffler tail cone falling off) will cause very poor running or even quitting altogether.
Look down the throat of any carb for the same size and brand engine from pre muffler days and post muffler days and the difference will be dramatic. For example An old OS .40 from the pre muffler days or transition days will have a venturi as much as half as small as a forty after mufflers became common place.
The old muffler tailcone falling off is a very common occurrence and almost always the engine either will stop altogether or run so poorly that an immediate landing is required.
John
Now what makes the difference is the venturi size and choke used. In years past when generally mufflers were not used and venturi suction was the only way to deliver the fuel, the venturi size and choke had to be kept to a minimum to be able to draw sufficient fuel. In later years when mufflers became common place, suddenly we now had a very simple way to boost fuel delivery. And with this the realization that we now could use a venturi of much larger area to boost power and this was a substancial boost at that. Of course the down side is the sudden loss of muffler pressure (pressure line popping off or a muffler tail cone falling off) will cause very poor running or even quitting altogether.
Look down the throat of any carb for the same size and brand engine from pre muffler days and post muffler days and the difference will be dramatic. For example An old OS .40 from the pre muffler days or transition days will have a venturi as much as half as small as a forty after mufflers became common place.
The old muffler tailcone falling off is a very common occurrence and almost always the engine either will stop altogether or run so poorly that an immediate landing is required.
John
Last edited by JohnBuckner; 11-15-2014 at 07:51 PM.
11-16-2014, 05:56 AM
#79
My Feedback: (1)
Who knows. Next thing we will tell people to carry the fueled up airplane with the nose high, use hemostats to pinch off the fuel line when it sits around on the ground for long periods when fueled, or keep the fuel lines as short and direct as possible. Or even to throttle back slightly if lean in the air. What's next, running the engine dry at the end of the day? Oh the humanity!
