Originally Posted by gbritnell
Steve, I got my hands on a very tiny Walbro for my 302 engine. I contacted a couple of the members of the BAEM club and asked them how they used the Walbro carb and what if any modifications needed to be made to it. I was told to buy the lowest pressure electric fuel pump (2-4 lbs) to start with. The only modification needed for the carb was to make an adapter plate and reduce the size of the venturi.
In all my searching I found some very good information on the functioning of these little carbs. The PDF files are too big to post so drop me a note at my email address and I'll send them to you.
I'll let you know how I make out with mine. I'm just finishing up the fuel tank, it's an aluminum 'Moon' type tank.
George
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George,
How did your test with the Walbro work out? I tried removing the 2 check valve flaps from the pump membrane so gas could flow unobstructed to the main fuel inlet from a gravity feed bowl. This didn't work and so my next thought is to make a small external fuel pump to keep the fuel in the main fuel inlet under 3-5 psi pressure which I think is what you were going to try. After studying the Walbro PDF, though, it seems that this will likely drastically change the operation of the carb as it meters fuel into the carb throat. It will effectively change the spring force, inlet lever spacing, timing and speed of reaction of the diaphragm. And if the carb ends up working at all it might be pretty inconsistent and difficult to tune. Until I studied the Walbro info, I didn't realize that the pressure pulses of each crank cycle were, in addition to pumping fuel into the fuel inlet, also used to gate fuel into the metering circuits on each crank cycle and the metering circuits were designed accordingly. I can see how the RC enthusiasts can use these carbs successfully since their single cylinder engines generate the same pressure pulses that the Walbro is expecting but on a V8 or in my case an H9, I'm not sure how we can use them. - Terry
Steve, I got my hands on a very tiny Walbro for my 302 engine. I contacted a couple of the members of the BAEM club and asked them how they used the Walbro carb and what if any modifications needed to be made to it. I was told to buy the lowest pressure electric fuel pump (2-4 lbs) to start with. The only modification needed for the carb was to make an adapter plate and reduce the size of the venturi.
In all my searching I found some very good information on the functioning of these little carbs. The PDF files are too big to post so drop me a note at my email address and I'll send them to you.
I'll let you know how I make out with mine. I'm just finishing up the fuel tank, it's an aluminum 'Moon' type tank.
George
*****************************************
George,
How did your test with the Walbro work out? I tried removing the 2 check valve flaps from the pump membrane so gas could flow unobstructed to the main fuel inlet from a gravity feed bowl. This didn't work and so my next thought is to make a small external fuel pump to keep the fuel in the main fuel inlet under 3-5 psi pressure which I think is what you were going to try. After studying the Walbro PDF, though, it seems that this will likely drastically change the operation of the carb as it meters fuel into the carb throat. It will effectively change the spring force, inlet lever spacing, timing and speed of reaction of the diaphragm. And if the carb ends up working at all it might be pretty inconsistent and difficult to tune. Until I studied the Walbro info, I didn't realize that the pressure pulses of each crank cycle were, in addition to pumping fuel into the fuel inlet, also used to gate fuel into the metering circuits on each crank cycle and the metering circuits were designed accordingly. I can see how the RC enthusiasts can use these carbs successfully since their single cylinder engines generate the same pressure pulses that the Walbro is expecting but on a V8 or in my case an H9, I'm not sure how we can use them. - Terry
