carburetor balance

K

Kevin in NZ

Junior Member
Does anyone know anything about balancing carbs when using an air filter ? I am think of fitting a B carb and have been advised to balance the carb.:) Dous it work ?
 
Unless you drive a lot in very dirty/dusty conditions, you don't need an air filter. It restricts the air flow, as you know, and there is no way to satisfactorily introduce air into the fuel/air mix to compensate
 
The theory is that any filter that actually filters has to lower somewhat the air pressure on the clean side of the filter. Since the fuel in the fuel bowl is at the higher, atmospheric pressure, the pressure differential pushes more fuel out of the jets causing car to run rich. Depending on other things, like whether the carb is set up marginally rich or lean and whether you have any air leaks around throttle shaft or gaskets, the effect may or may not be significant.

Here's some pictures of a B carb that has been modified for air filter use--the float bowl headspace has to be vented to the air intake area, and the normal vent has to be plugged. Ugly. It worked, but the carb had other issues that caused me to give up on it.

I agree with others who said just don't bother with the air filter, at least if most of your driving is on paved roads. Maybe you have more dirt roads in NZ?

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Steve
 
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Some filters, K&N for example, do not create much pressure drop. If you have a filter and the GAV adjusts to the normal range, you do not need the air balancing that is pictured.
 
I just put an airmaze on mine yesterday and it runs good with the adjusting knob on the choke turned about 3/4 of a turn to the left from full closed. Before I put the filter on I only had to turn the adjustment 1/4 turn. Will It hurt anything to run with the adjustment at 3/4 turn? I am having a hard time with the idea of not using an air filter because of all the bugs, dirt and everthing else floating around in the air. Just seems to me that leting all that stuff get into the carb can't be good.
 
I am a firm believer that air breathers do more harm than good on the model A. Air breathers and running with the GAV opened more than normal will cause the spark plugs to run black and sooty. The oil in the crankcase will become diluted with unburned fuel. A too rich mix will cause some of the raw unburned fuel to wash the oil in the cylinder walls past the rings and into the oil pan where it thins the oil and reduces its ability to lubricate the bearings. Besides all of this breathers reduce breathing and power. As for the Bugs, anything entering the cnoke end of the carb will go right up the intake manifold, be burned and go right out the exhaust. Anything that would clog the jets will have to enter via the fuel, not the throat of the carb.
 
Georgew48 said:
I just put an airmaze on mine yesterday and it runs good with the adjusting knob on the choke turned about 3/4 of a turn to the left from full closed. Before I put the filter on I only had to turn the adjustment 1/4 turn. ...QUOTE]

I'm not questioning what George says, but can someone explain to me how his experience makes sense? My understanding is that, if anything, an air filter causes a motor to run too rich. Opening the GAV lets in even more fuel. What am I missing???

Also, regarding Pelikan's article linked by Benson, I wonder if the auto mechanics who have the consensus quoted below were assuming "balanced" carburetors, as all carbs since the mid-30's have been.

"automotive engineers regularly size air filter surface areas at one-half an engines cubic inch capacity",

If that's really all there is to it, I wonder why manufacturers have gone to the bother and expense of building in the balancing plumbing for all these years.

Steve
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Steve,

I agree that it makes no sense that 3/4 turn from 1/4 is needed after installing a filter.

Also GeorgeW48 says the filter is an Airmaze (a wire mesh filter , which has little restriction)!! This makes no sense there should be little or no restriction unless filter is REALLY dirty.

One thing that comes to mind is that in past I have seen this behavior where the GAV adjustment changes radically every time you turn it and is not consistent. Here is what I found.

IF the the carb is a mid 29 or older and has the brass GAV seat. Sometimes someone does not tighten the GAV seat in casting when it is installed (Or tightens the GAV NEEDLE WAY too tight) and then they screw the needle down hard because the gas is leaking around the GAV seat washer.

Then the needle gets stuck in the GAV seat taper. When rod is turned to adjust, the GAV seat is being unscrewed from the casting. The result that the flow of the gas is unpredictable and way too much or too little depending upon if the gasket is sealing or not.

2. Another possibility is that some of the REPRO choke rods have a knob on the top of rod that is not fastened tightly to the rod. The knob can then be turned in either direction while the rod does not move.

Just some things to check!




steve s said:
Georgew48 said:
I just put an airmaze on mine yesterday and it runs good with the adjusting knob on the choke turned about 3/4 of a turn to the left from full closed. Before I put the filter on I only had to turn the adjustment 1/4 turn. ...QUOTE]

I'm not questioning what George says, but can someone explain to me how his experience makes sense? My understanding is that, if anything, an air filter causes a motor to run too rich. Opening the GAV lets in even more fuel. What am I missing???

Also, regarding Pelikan's article linked by Benson, I wonder if the auto mechanics who have the consensus quoted below were assuming "balanced" carburetors, as all carbs since the mid-30's have been.

"automotive engineers regularly size air filter surface areas at one-half an engines cubic inch capacity",

If that's really all there is to it, I wonder why manufacturers have gone to the bother and expense of building in the balancing plumbing for all these years.

Steve
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Click to expand...
 
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Kevin , I note you said carbs, are you thinking of more than one ?? therfore if more than one they need to be balanced, I run B on delivery , no filter other than an air maze , no problem. My slant has a weber set up & boy is this nice plus you get the air filter, not orig but great for touring & mpg, or is that KpL.
 
It dosen't make any sense to me either but that's what it's doing. The filter is brand new so not dirty. My GAV works just as it is siuppose to with the filter off but with it on I have to open it more than usual. The engine seems to run great with the filter on and the GAV opened 3/4 of a trun but I sure don't want to cause and long term problems so I mifght just remove it and eat the cost of the filter.
 
If you do put a filter on a B carb, the B carb has a larger dia on the inlet than the A card and an A filter will not fit.
 
Fred K-OR said:
If you do put a filter on a B carb, the B carb has a larger dia on the inlet than the A card and an A filter will not fit.
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You're right. I used concentric pieces of radiator hose and hose clamps to attach mine, a very nice product made by What's-It, as I recall. Alas, my rigging was inadequate and I lost the unit going down the road. I heard a strange noise, and after a few miles of puzzling over what it might have been, turned around to search for it but without success.

Steve
 
steve s said:
You're right. I used concentric pieces of radiator hose and hose clamps to attach mine, a very nice product made by What's-It, as I recall. Alas, my rigging was inadequate and I lost the unit going down the road. I heard a strange noise, and after a few miles of puzzling over what it might have been, turned around to search for it but without success.

Steve
Click to expand...

I had a similar problem. I heard a noise and looked back and saw my horn on the road behind me. Lucky I did not run over it.
 
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