Tanaka QBM-23N "Bike Bug" fuel and vent line questions

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Pappa Jim

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Aug 19, 2022
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I'm new to motorized biking. My interest came out of necessity as I don't drive a car. I'm legally blind. I found a Tanaka QBM-23N style engine that is complete. But all the fuel and vent lines have been removed. So, I've taken some pics of the gas tank (to show where there are vent holes, the carburetor and the fuel pump. What I know so far is that you can hook up a fuel line to the in and out nipples on the fuel pump, and when you blow on the in line, air comes out like it should from the out line. There are three nipples on the carb. One is big and must be a vent. another smaller one is right next to it on the upper part of the carb. the other nipple is closer to the bottom. I think this carb is plugged. The engine has spark and will start with a shot of starting fluid. Ok, here come the pics. I'm pretty sure there is a check valve that's supposed to be in the primer bulb, but it's missing. HELP!
 

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Sidewinder Jerry

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Dec 19, 2011
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Carburetors work like this they suck fuel into them. If you believe the carb is clogged disassemble it. The intake side will have a fine mesh screen on it. That'll have to be cleaned along with cleaning all of the jets and passageways. I'm very near-sighted; without glasses, I couldn't drive. However, I can see very well without glasses if something is within one foot of my eyes. Cleaning a carb may be something you'll need help with.


I also tell all small engine users to use 100% ethanol-free gas. This has nothing to do with octane levels. It'll have it on the pump 100% gas.
 
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Pappa Jim

New Member
Aug 19, 2022
19
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3
74
Wisconsin
Carburetors work like this they suck fuel into them. If you believe the carb is clogged disassemble it. The intake side will have a fine mesh screen on it. That'll have to be cleaned along with cleaning all of the jets and passageways. I'm very near-sighted; without glasses, I couldn't drive. However, I can see very well without glasses if something is within one foot of my eyes. Cleaning a carb may be something you'll need help with.


I also tell all small engine users to use 100% ethanol-free gas. This has nothing to do with octane levels. It'll have it on the pump 100% gas.
Thanks Jerry. I took the carb apart and just as you said, that little screen was plugged up. So I cleaned it good as well as the jets and other passageways. I'm going to put it back together today and I'm betting I'll get that little motor to fire up. Thanks so much for the input.
 
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Sidewinder Jerry

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Dec 19, 2011
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Thanks Jerry. I took the carb apart and just as you said, that little screen was plugged up. So I cleaned it good as well as the jets and other passageways. I'm going to put it back together today and I'm betting I'll get that little motor to fire up. Thanks so much for the input.
Be sure to put a fuel filter on the intake line in the tank.
 

Sidewinder Jerry

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Dec 19, 2011
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The ethanol fuel is another issue. It is like putting sugar into your gas tank. In my small town, we finally have a station that sells 100% gas. For this reason, I now use a 5-quart gas tank. This gives me a greater range without having to stop at stations that don't sell 100% gas. I have a 4 stroke.
 

Pappa Jim

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Aug 19, 2022
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Wisconsin
The ethanol fuel is another issue. It is like putting sugar into your gas tank. In my small town, we finally have a station that sells 100% gas. For this reason, I now use a 5-quart gas tank. This gives me a greater range without having to stop at stations that don't sell 100% gas. I have a 4 stroke.
Good advice about the gas thing Jerry. And here's something else I discovered after taking the carb completely apart on my "Bike Bug" engine as well as FINALLY getting an answer from a Tanaka (the makers of that engine) technician. First, the carb has been apart before and somebody stuck a screen in the intake side just ABOVE the hole where the fuel comes into the bowl. So it wasn't doing any good anyway. second, the part of the carb that has the bowl on it is attached by two small screws. One side is broken and some kind of glue or something was used to put it back together. Unbelievable! No wonder that poor little motor wouldn't run. Sucking air in all the wrong places with dirt in every dang hole, jet and nozzle. But...I'll find a way to get it running CORRECTLY!
 
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wrench

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Aug 20, 2019
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the part of the carb that has the bowl on it is attached by two small screws. One side is broken and some kind of glue or something was used to put it back together. Unbelievable! No wonder that poor little motor wouldn't run. Sucking air in all the wrong places with dirt in every dang hole, jet and nozzle. But...I'll find a way to get it running CORRECTLY!
Start by getting a new carb
 
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Sidewinder Jerry

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Yes. A new carb is definitely needed. And after measuring the opening on the intake manifold, there are tons of reasonably priced, brand new carbs to choose from. thanks guys!
I replaced the $70 non-adjustable Walbro carburetor with a $15 adjustable carburetor from eBay. Even got a second one and carry it as a spare. The performance went way up on the engine.
 
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Pappa Jim

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Aug 19, 2022
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I just want to thank all of you guys for taking valuable time from your lives to help me out with this "Bike Bug" engine on which there isn't a lot of info available. I think at this point I'll keep the engine and tinker with it as it's a challenge and I like challenges. Yet I like to ride as well, so I'm looking to build something that's in the "newer" technology. Like a 4 stroke with a gas tank on the bike's backbone, clutch...you get the picture. THANKS GUYS!
 

Mossy

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Yes. A new carb is definitely needed. And after measuring the opening on the intake manifold, there are tons of reasonably priced, brand new carbs to choose from. thanks guys!
Make a note to the size of the jets in the old carb... Put them in the new one
 
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