You're welcome.mrquadriga said:
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Anonymous
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Keith, I am completely convinced, I just wish I understood! It's like, a religious experience, but on a bike, at least, I expect things to make sense in the physical world. :lol:
Work with me here. The fuel is pulled out of the bowl, through the jets. That fuel is replaced by fuel from the tank. So... the net pressure in the bowl should stay at its starting pressure. Conceptually, bowl vents aren't even necessary to keep bowl pressure at atmospheric. And as there is little net movement of air through the vent lines, how does a vortex form? Unless it is due to passing air, like a venturi effect? That is the only plausible explanation I have thought of. Do you suppose that's it?
Work with me here. The fuel is pulled out of the bowl, through the jets. That fuel is replaced by fuel from the tank. So... the net pressure in the bowl should stay at its starting pressure. Conceptually, bowl vents aren't even necessary to keep bowl pressure at atmospheric. And as there is little net movement of air through the vent lines, how does a vortex form? Unless it is due to passing air, like a venturi effect? That is the only plausible explanation I have thought of. Do you suppose that's it?
Well, bowl vents are necessary to allow the jets to draw fuel easily.bazango said:
If the venting is poor, the jets can't draw fuel easily so there must be a counter vacuum building up. I don't know. The "vortex" idea was told to me by a guy at Dynojet.
I don't worry about the science behind it. I just know that with the engine flowing more freely, the standard bowl venting isn't adequate. A vortex, turbulence or ? compromises the venting and the jets don't draw fuel easily.
G
Guest
Guest
carb vents
carb vents
First, I know almost nothing about carburetors.
Second, carbs should need a vent for one of the reasons that a gas tank needs a vent, to accomodate thermal expansion and contraction. If the bowl becomes pressurized from heating, a lot more gas should be forced through all the jets. I would think that this would not happen unless the engine is off. Same thing should apply to cooling.
The Venturi Principle is fundamental to the operation of carburetors. When air blows across an orifice, the pressure behind the orifice lowers. If that orifice is the carb vent, pressure in the carb would be lowered, exactly what isn't desired. A solution might be to add a tube to the vent orifice, and run the end of the tube to a region of still air, where there can't be any wind across the opening of the tube.
As a test, I put a 3/8" vinyl tube in a glass of water, and blew compressed air past the end, and water was pulled about 3/4" up into the tube.
As for me, I used to own an '82 GS650G. The gasket at the base of the cylinder failed at about 6K, but other than that, the only maintenance that it needed for 25K miles was fluid and filter changes, two sets of tires (the second one at 24K), plugs and two or three valve adjustments. I bought an '82 GS850G that runs well up to about 25 mph and then accelerates very slowly. Based on these forums, I'm going to start with the fuel petcock and hoses, replace the air filter and seal the air box (it needes it). Only then, if it needs it, I'll disassemble and clean the carbs and put in Robert's O-ring set.
This is a great forum!
carb vents
First, I know almost nothing about carburetors.
Second, carbs should need a vent for one of the reasons that a gas tank needs a vent, to accomodate thermal expansion and contraction. If the bowl becomes pressurized from heating, a lot more gas should be forced through all the jets. I would think that this would not happen unless the engine is off. Same thing should apply to cooling.
The Venturi Principle is fundamental to the operation of carburetors. When air blows across an orifice, the pressure behind the orifice lowers. If that orifice is the carb vent, pressure in the carb would be lowered, exactly what isn't desired. A solution might be to add a tube to the vent orifice, and run the end of the tube to a region of still air, where there can't be any wind across the opening of the tube.
As a test, I put a 3/8" vinyl tube in a glass of water, and blew compressed air past the end, and water was pulled about 3/4" up into the tube.
As for me, I used to own an '82 GS650G. The gasket at the base of the cylinder failed at about 6K, but other than that, the only maintenance that it needed for 25K miles was fluid and filter changes, two sets of tires (the second one at 24K), plugs and two or three valve adjustments. I bought an '82 GS850G that runs well up to about 25 mph and then accelerates very slowly. Based on these forums, I'm going to start with the fuel petcock and hoses, replace the air filter and seal the air box (it needes it). Only then, if it needs it, I'll disassemble and clean the carbs and put in Robert's O-ring set.
This is a great forum!
Re: carb vents
Re: carb vents
The tube is what's causing or contributing greatly to the problem. Many stock vent tubes are 16-18" long and run to still air under the seat. Even if you try cutting the stock vent tube much shorter, it doesn't work either. You still get fuel starvation.
If you have pod filters, you want to remove the tubes and leave the vent ports open.
Re: carb vents
The solution you mention here wouldn't work.themess said:
The tube is what's causing or contributing greatly to the problem. Many stock vent tubes are 16-18" long and run to still air under the seat. Even if you try cutting the stock vent tube much shorter, it doesn't work either. You still get fuel starvation.
If you have pod filters, you want to remove the tubes and leave the vent ports open.