Walbro Glow Carb
04-20-2003, 03:55 PM
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Walbro Glow Carb
I saw a thread for a Ryobi glow conversion using a Walbro WT-499 carb (Glow Zenoah G-23). I'd like to find a glow carb that is designed for engines in the 35-41cc range. I'm thinking the WT-499 venturi is a little small for a 31cc engine. Anyone know how to find the Walbro number?
Thanks
Garry
Thanks
Garry
04-20-2003, 07:26 PM
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WT-499
The Walbro wt-499 is NOT an alcohol carb. Walbro does not make Alky carbs. The WT499 is a gas carb with bigger than normal jets in it. So it flows enough fuel to work fine with Alky.
The Walbro master book has everything but jet size in it . So you can't just look for a bigger carb with big jets in it. About all you can do is find a carb that fits right and pop the welch plugs and enlarge the jets. You need to make the jets 2x the sq" size, not 2x the dia. Sort of hit and miss.
With the Ryobi having a factory redline of 7500 RPM the WT499 will pass enough air. Of course if you ignor the red line and twist it up to 8500 then the WT 499 isn't enough.
Its all part of the fun of converting engines
The Walbro master book has everything but jet size in it . So you can't just look for a bigger carb with big jets in it. About all you can do is find a carb that fits right and pop the welch plugs and enlarge the jets. You need to make the jets 2x the sq" size, not 2x the dia. Sort of hit and miss.
With the Ryobi having a factory redline of 7500 RPM the WT499 will pass enough air. Of course if you ignor the red line and twist it up to 8500 then the WT 499 isn't enough.
Its all part of the fun of converting engines
04-21-2003, 06:58 AM
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Walbro Glow Carb
I'm the fellow that did the Ryobi 31cc glow mod. The WT499 flowed plenty enough fuel to keep the 31cc happy. As a matter of fact, I had to screw the needles quite a ways in to lean it out for 5% castor 0% nitro fuel. I also tried 15% nitro 18%, which requires an even richer setting because of the additional nitro, and the carb kept the engine happy at darn close to 8000rpm. I didn't dare go past that for fear the stamped conrod might blow up in my face.
My rough guess is that the WT499 will feed up to 40cc at normal RPMs no problem. Now whether the venturi size will flow enough air for that big an engine and still maintain good volumetric efficiency to produce optimum power I do not know.
My rough guess is that the WT499 will feed up to 40cc at normal RPMs no problem. Now whether the venturi size will flow enough air for that big an engine and still maintain good volumetric efficiency to produce optimum power I do not know.
04-21-2003, 07:18 AM
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Walbro Glow Carb
BTW, Terry is right about it being part of the fun of converting engines. In fact, I'm so impressed with how several of my smaller conversion motors run on WT-499 and glow fuel, I had Terry order me 3 more of them Walbro critters. 
I will say this though, 31cc or 2 c.i. is about as big a glow conversion I would do anyways. Much bigger than that, then the sheer bulk of the glow fuel you've got to carry in the plane starts to work against any power gain you might realize. Plus at 40cc and up, the power to weight ratio of most gassers starts to become very competitive with glow setups.
I will say this though, 31cc or 2 c.i. is about as big a glow conversion I would do anyways. Much bigger than that, then the sheer bulk of the glow fuel you've got to carry in the plane starts to work against any power gain you might realize. Plus at 40cc and up, the power to weight ratio of most gassers starts to become very competitive with glow setups.
