My 49cc needs more torque for hills!

[markjs]

So I'm running a 44 tooth sprocket, which is what most kits come with. It almost is able to go up the hill I need it to, but just can't, and I can keep it moving with pedal assist, but not without. I need it to be able to do that without pedaling or I need to upgrade it, one of the two. It's just a backup bike and only for short trips.

So the question is, will a 48 tooth sprocket likely be enough? That's only 4 teeth, but I need it to be able to struggle up that hill without pedaling. I don't mind pedal assist to keep the RPMs up, but ideally my "standard" is that I need an engine that can pull the main hill in town without pedaling. I usually pedal anyway, but I like to be able to take breaks, and not have to go the whole hill...

My PK80 which is presently not running right, will do that when it is running right. About once a week I ride it up the hill without pedaling at all and it makes it just fine, just to make sure it hasn't lost power. I'm paranoid after a recent breakdown, and it broke down again, so I'm pretty frustrated!

Anyway anyone with experience with hills, please LMK if you think 48 is enough it will likely make it, or if I have to go like 52? That would be a horrible top speed if I had to go that big though I imagine?

Ideally I just want it to get up a moderate hill without pedal assist and at least keep up with e-bikes like at least around 20mph.

What size do you think I probably need?

It does appear to still be running a bit lean. Might need re-jetted too...

 

[Sidewinder Jerry]

So I'm running a 44 tooth sprocket, which is what most kits come with. It almost is able to go up the hill I need it to, but just can't, and I can keep it moving with pedal assist, but not without. I need it to be able to do that without pedaling or I need to upgrade it, one of the two. It's just a backup bike and only for short trips.

So the question is, will a 48 tooth sprocket likely be enough? That's only 4 teeth, but I need it to be able to struggle up that hill without pedaling. I don't mind pedal assist to keep the RPMs up, but ideally my "standard" is that I need an engine that can pull the main hill in town without pedaling. I usually pedal anyway, but I like to be able to take breaks, and not have to go the whole hill...

My PK80 which is presently not running right, will do that when it is running right. About once a week I ride it up the hill without pedaling at all and it makes it just fine, just to make sure it hasn't lost power. I'm paranoid after a recent breakdown, and it broke down again, so I'm pretty frustrated!

Anyway anyone with experience with hills, please LMK if you think 48 is enough it will likely make it, or if I have to go like 52? That would be a horrible top speed if I had to go that big though I imagine?

Ideally I just want it to get up a moderate hill without pedal assist and at least keep up with e-bikes like at least around 20mph.

What size do you think I probably need?

It does appear to still be running a bit lean. Might need re-jetted too...

Are you using 26" wheels? The 49cc 2 stroke at best is only generating around 2 hp. Depending on total weight and what percent grade hill you're talking about a reduction of 21.32\1 (52t) still may not be enough with no pedal assist.

To do 20 mph on 26" wheels using a 52t requires an engine rpm of 5513. So you could probably go slightly faster than 20 mph on level ground.

 

[markjs]

Are you using 26" wheels?

Yes, an old Peugeot "mountain bike", from the era when "mountain bike" pretty much meant a multispeed road bike with a sturdier frame

I'll send a pic of the plug in a few, it looks lean to me, but not bad enough it would probably just roar up the hill if the carb was tuned better. Besides the needle is set to maximum rich as is... Needs jets to go any richer.
.

 

[Gordy]

Perhaps just a bigger sprocket will do the trick.

 

[markjs]

Are you using 26" wheels? The 49cc 2 stroke at best is only generating around 2 hp. Depending on total weight and what percent grade hill you're talking about a reduction of 21.32\1 (52t) still may not be enough with no pedal assist.

To do 20 mph on 26" wheels using a 52t requires an engine rpm of 5513. So you could probably go slightly faster than 20 mph on level ground.

It does seem to do quite well revving out, if you can build the RPMs. I'm sure I've had it over 7K briefly.

So you think a 52 tooth would be the sweet spot for hill climbing torque? If I can just get it to run up the hills and around our small four miles across little town, it will be golden! (Speed limit is 25 everywhere except one road which is 30.)

20MPH is a minimum speed I'd like it to top out at. I'm tempted to try a 48, but maybe a 52 is more likely to work?

 

[darwin]

Try going up the hill w/o your carb breather filter in it. See if there's any difference. Also you have a screen spark arrestor in the muffler on that, make sure it isn't clogged up with carbon, or try it w/o that. Only do one at a time to see if just 1 change gives you improvement so it's isolated. Arrester you can just leave out or in clean. If the filter out improves you need a better filter system........checking your valve adjustment might help if it's out of spec, easy things 1st...................Saw 49cc and assumed this was a 142f motor, please disregard post!

 

[Chainlube]

Time for a nice new leg burning exhaust to create the torque you need for those hills.

 

[robe]

That's what I was going to suggest, ditch the stock exhaust. You will have to re jet the carb as it is on the border of being too lean now.

You could open up the stock exhaust, might help a bit but you will have to still do something with the carb.

 

[MinimumVK]

What i found out about my bike is that when i took off the exhaust end cap it was able to pull off without pedal assist and climb any hill it saw, however it lost about 20km/h of speed which i didnt like. It made it too rich after 45km/h and just 4 stroked from there. But the torque was amazing! (YD100 with 44t sprocket)

 

[robe]

What i found out about my bike is that when i took off the exhaust end cap it was able to pull off without pedal assist and climb any hill it saw, however it lost about 20km/h of speed which i didnt like. It made it too rich after 45km/h and just 4 stroked from there. But the torque was amazing! (YD100 with 44t sprocket)

Probably need a bit of back pressure. You can open up the baffles and put in a larger outlet pipe. I did that to one and put it on the end of an extractor pipe and am really happy with it. Not too loud with good torque and reasonably high rpm.