Weedwacker bike weight limit?

You could port a weedwacker engine and put a little expansion chamber on it for more power. Friction drive is probably best for under 49cc engines. Chainsaw would be better though.
 
You could port a weedwacker engine and put a little expansion chamber on it for more power. Friction drive is probably best for under 49cc engines. Chainsaw would be better though.

How would you Port an engine that small? Is there any easy way without needing a machine shop?
 
Ya all you need is a dremel and some sandpaper. Some of those engines have a divider in the middle of the port you could delete but not all have it. They make little expansion chambers for the hpi baja and rc engines you could adapt. I actually want to that to see if it actually helps the top speed or anything. I have 3 power heads and a chainsaw but they all have carb problems. I have an old 31cc ryobi that I think needs a magneto, a 25cc homelite that runs but has a bad carb and an old hedge trimmer engine that stripped the key on the flywheel. The diaphragm carbs are a pain. If they were slide carbs it would be much better. Maybe I could adapt the stock nt carbs for one of those engines, perhaps the homelite chainsaw.
 
Ya all you need is a dremel and some sandpaper. Some of those engines have a divider in the middle of the port you could delete but not all have it. They make little expansion chambers for the hpi baja and rc engines you could adapt. I actually want to that to see if it actually helps the top speed or anything. I have 3 power heads and a chainsaw but they all have carb problems. I have an old 31cc ryobi that I think needs a magneto, a 25cc homelite that runs but has a bad carb and an old hedge trimmer engine that stripped the key on the flywheel. The diaphragm carbs are a pain. If they were slide carbs it would be much better. Maybe I could adapt the stock nt carbs for one of those engines, perhaps the homelite chainsaw.

Im not too familiar with porting, we are talking about the intake port right?
 
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Im not too familiar with porting, we are talking about the intake port right?

No! absolutely don't attempt to 'port' a weedeater engine!

Espcially if it's a decent model like an Echo or Tanaka. You'll either really muck up the cylinder and ruin it or cause a tuning change that ruins it's power spread. Honestly I don't know where people think you can apply China Girl engine tuning techniques to precision little weedeater engines. You'll just end up ruining what was a good running engine. The best thing you can hope for is to check the spark arrester, if so equipped, and clean the mesh screen and maybe fab a small performance aircleaner to the intake, but that will take some serious tuning skill. Weedies as a rule like RPMs and should be 'geared' conservatively. 1 and 1/8" inch diameter driver friction wheel is within the ballpark for something that might clim moderate hills with leg assist. At this engine size the engines should be bicycle assistance engines, not the primary power source.

Read this thread in MotorBicycling's DIY subforum: https://motorbicycling.com/threads/minimalist-fd.62572/

Cannonball2 builds some of the most sanitary light bike drives on any Motorized bike forum and should be an inspiration for those who want to build DIY friction drives, the engine in his thread keeps it's auto clutch working so you don't have to raise the engine off the tire at stops.

dscf2055-jpg.85016
 
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No! absolutely don't attempt to 'port' a weedeater engine!

Espcially if it's a decent model like an Echo or Tanaka. You'll either really muck up the cylinder and ruin it or cause a tuning change that ruins it's power spread. Honestly I don't know where people think you can apply China Girl engine tuning techniques to precision little weedeater engines. You'll just end up ruining what was a good running engine. The best thing you can hope for is to check the spark arrester, if so equipped, and clean the mesh screen and maybe fab a small performance aircleaner to the intake, but that will take some serious tuning skill. Weedies as a rule like RPMs and should be 'geared' conservatively. 1 and 1/8" inch diameter driver friction wheel is within the ballpark for something that might clim moderate hills with leg assist. At this engine size the engines should be bicycle assistance engines, not the primary power source.

Read this thread in MotorBicycling's DIY subforum: https://motorbicycling.com/threads/minimalist-fd.62572/

Cannonball2 builds some of the most sanitary light bike drives on any Motorized bike forum and should be an inspiration for those who want to build DIY friction drives, the engine in his thread keeps it's auto clutch working so you don't have to raise the engine off the tire at stops.

dscf2055-jpg.85016

Thanks for the reply, that is exactly what’s I was looking for! I probably won’t port the engine just because of my inexperience, but if I install a small spindle it should give decently torque and a low speed. Thanks
 
Thanks for the reply, that is exactly what’s I was looking for! I probably won’t port the engine just because of my inexperience, but if I install a small spindle it should give decently torque and a low speed. Thanks

Hi Andrew.

Please look carefully at Cannonball2's description of his weedie conversion. He's using the twin ball bearing weedeater line head driver off of an old Echo 21 cc as the carrier for the friction drive roller. If you try to run the roller from the engine itself, if there's no bearing support off the clutch it drives, it's side loading will destroy the clutch drive in short order. Especially if it's a cheap weedeater like a Ryobi Toro, Poulan or other US domestic produced weedie. It will be worth your time to keep an eye out at small engine repair shops, Craigslists, garahe sales and other venues to find an older, quality, curved shaft weedeater You use the lower assembly that drives the line cutter advance head. it has two fair sized ball bearings that can handle the side loading a friction drive will impose on the drive roller, otherwise you have to support both sides of the friction roller which increases the complexity of your installation.

Also take into account that you will need some fabrications skills and tools to cut and drill angle iron, steel sheeting, and tubing to make this work. It will not be easy for a beginner.
 
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