New here from Australia. Just acquired 200w street legal motorised bicycle.

Hi all, I found this place when looking for ways to improve performance on a 48cc motor. I have not ridden a bicycle since I was a kid but recently picked up a pre-fab motorized bike from a guy who builds them. It's a $90 supermarket mountain bike with a 48cc 2 stroke motor that has been de-tuned to 200w to comply with Australian laws.

It's been a learning curve for me just getting used to riding a bike again, let alone a motor powered one. I find the cars very daunting and can never hear them coming up behind me because of the exhaust noise. I've realized that becoming traffic savvy on a bike is an art in itself, motor or no motor. Fortunately in my area there are several miles of trails and tracks that cut through to all of the major parts of the region, i'm utilizing them almost 100% of the time, and only venturing into traffic when I have no other option. I've done about 30 miles in total so far, and really like it as a mode of transport, I just wish there were more bike lanes on the roads.

The bike itself is okay for it's limited 200 watts I suppose, but it really struggles up hills and requires pedal assistance big time. I weigh 110kg (230lbs), so i'm really up against it. The manual says that the engine will increase in torque as it is run in, but I feel that I'm going to want more. The company that builds the engine can provide an upgrade kit which de-restricts the engine and gives it the power of a regular 48cc, but this would make it illegal to use.

Rather than buy the upgrade kit (which appeared to be just an exhaust pipe and a carburetor) I was wondering what I could try on the existing combination to improve the torque and a little bit of top speed? The guy I purchased the bike from showed me a 200w inlet manifold gasket and it had a hole in it about a half or even maybe a third of the size of the carby and manifold throat, if I replace this with a gasket with a larger opening, will I gain power? I suspect that the exhaust might also just have a restrictor plate in it, and if I removed that as well, would I theoretically see an increase in torque or power, and is it likely that could I adjust my existing carby to work with the better breathing capability?

Sorry to bombard you with so many questions, and I hope i'm posting in the correct forum.

An Expansion Chamber exhaust will wake it up.

As a newbie myself, I can't tell you how to make your bike quieter, but as a very experienced cyclist, I can tell you that the best way to handle traffic is a mixture of passive-aggressive attitude.
You need to be aggressive enough so they don't just run you off the road - which they will, given half the chance - but at the same time passive enough so you don't get flattened.
Ease into it slowly, you're on the right track utilizing trails and side streets whenever possible and keeping your time on busier roads to a necessary minimum.
If your ride counts as a 'bicycle' by local law, take advantage of bike lanes and such, but be courteous to cyclists, skateboarders, etc. who need those facilities even more than you do.
Get a mirror if you don't already have one - maybe even 2 - but do ALWAYS look over your shoulder, there's no substitute for that.
Wear something like a reflective safety vest and a helmet, makes you more visible and they might take you more seriously.
Or, you could go the distracted history professor route and ride in an Irish fisherman's cap, tweed jacket (with leather elbow patches) and torn jeans, accessorized with glasses and long hair. They might give you a wider berth......

KCvale said:

An Expansion Chamber exhaust will wake it up.

Click to expand...

Thanks, would I do that and leave the rest of the engine as is? Or should I do it in conjunction with removing whatever the engine builder has done to reduce the power?

Wolfie65

As a newbie myself, I can't tell you how to make your bike quieter, but as a very experienced cyclist, I can tell you that the best way to handle traffic is a mixture of passive-aggressive attitude.
You need to be aggressive enough so they don't just run you off the road - which they will, given half the chance - but at the same time passive enough so you don't get flattened.
Ease into it slowly, you're on the right track utilizing trails and side streets whenever possible and keeping your time on busier roads to a necessary minimum.
If your ride counts as a 'bicycle' by local law, take advantage of bike lanes and such, but be courteous to cyclists, skateboarders, etc. who need those facilities even more than you do.
Get a mirror if you don't already have one - maybe even 2 - but do ALWAYS look over your shoulder, there's no substitute for that.
Wear something like a reflective safety vest and a helmet, makes you more visible and they might take you more seriously.
Or, you could go the distracted history professor route and ride in an Irish fisherman's cap, tweed jacket (with leather elbow patches) and torn jeans, accessorized with glasses and long hair. They might give you a wider berth......​

Click to expand...

Bicycle commuting does take a while to get used to, motorized or not.
ALWAYS look over your shoulder before changing lanes or turning and NEVER assume others (drivers) will do the right thing.
Stop lights/signs may be ignored, they might cut you off, they might not see you - there are many drivers in whose world anything smaller than a 750 cc motorcycle simply doesn't exist - they might even autohate you simply because you're not in a car.
Then there's the drunk, the drugged, the senior, the texters........
Short trips to the supermarket on side streets sound like a good start, build up to busier streets slowly.
One potential drawback of bike trails is that they could lull you into a false sense of security, making you freak out when the trail ends and you have to suddenly deal with traffic again.

I've been looking over my shoulder since you first mentioned it, and it helps a lot. It was just hard at first to force myself to turn away from the direction I was going in. It's definitely a completely different experience to anything I've done before.

Interesting thread. It's hard for me to imagine having an 'alien' feeling on a bike.

All the same, though, it does sound as if you're doing it right. Get your footing in traffic nice and slow. There's no rush.

Wofie's advice about high-vis clothing is good. If nothing else, you want to take away any excuse for them to say, "But I didn't see him". And autos do give reflective vests a bit of respect.

I strongly advise two mirrors. Maybe it sounds like overkill. But having two different rear points of view gives you a better notion of what's going on behind you. Personally, I don't turn my head much. (Though I would not claim that it's bad advice) I do watch both of my mirrors a good deal. And I especially look them over thoroughly when I'm about to cross traffic.

I won't claim that a car can never, never sneak up on me. But it happens only very rarely.

I'd actually advise you to leave your motor just the way it is and not even try to get more speed out of it. But I'll admit that I'm a bit more conservative than most on the issue of top speed. But I do think that twenty is more than enough. Anyone who wants to go faster really shouldn't be doing it on a motor assisted bicycle. They should be moving up to scooters. Plus this way you'll stay legal. And that don't hurt things one little bit.

Devil's Advocate said:

Thanks, would I do that and leave the rest of the engine as is? Or should I do it in conjunction with removing whatever the engine builder has done to reduce the power?

Click to expand...

An NGK 5944 (BPR7HIX) Iridium spark plug IF you have a slant head stock engine will help too.

Chances are little else was done to hamper performance other than maybe a restricted (smaller) intake gasket.

Re the newbies looking behind them is good but scary thing:

A game changer for me was realising how stable standing fully upright with most weight on one pedal is. I find it gives me similar confidence to take my eyes off the road as i would have when walking. It wasnt that i couldnt see the road was clear ahead, but that i didnt trust myself not to wobble while looking behind.

also, as u can twist your body much more easily, the head twist is less extreme.

Just putting it out there but I don't think the motor is 200w. Cops don't care enyway as long as you pedal thay can't say enything. I think it's a big lie 200w enyone know of this