My motor tops out at 30km/h, how do I fix this??

[StanlyManly]

So the fastest I've EVER gotten my motor was 35km/h, on a long stretch, at full throttle. Yes, I've run it in for 100km, with a 16:1 ration.. Now I'm running a 50:1 ration with 95 octane petrol, fully synthetic oil, and I have my NGK B7HS gapped at 35mm as recommended by some bike guys.

I'm still getting slow speeds! I hope someone can help me and suggest heaps of things I can do and run me through it! Everything is stock, including my NT carb. Apparently a lot of people have an air leak issue, but I'm lost on what to do!

I'd really appreciate the help!

 

[Theon]

Did you retune the carb (air fuel) mix when swapping to 50-1?

 

[StanlyManly]

Did you retune the carb (air fuel) mix when swapping to 50-1?

Yes, I moved the c-clip, if that's what you're referring to. Or do you mean the jets? I'm still working through it, but the spark plug is still a little dark.

 

[Theon]

Correct jet in carb is what will likely get you a little more top end, Not all of these motors were created equal and there are a few things that could be limiting its performance.
proper port matching of manifolds, inlet duration, compression ratio, ect.
Clogged exhaust from running 16 to 1?.

 

[StanlyManly]

Correct jet in carb is what will likely get you a little more top end, Not all of these motors were created equal and there are a few things that could be limiting its performance.
proper port matching of manifolds, inlet duration, compression ratio, ect.
Clogged exhaust from running 16 to 1?.

I've actually cleaned out the exhaust my best, with a metal stick. Is there a more effective way?

But when you say a better jet will do more top end, that won't necessarily help my speed problem, from 30km/h to 60km/h will it? I want it to go at least 40-50km/h!

I wouldn't have a clue about the manifolds, inlet duration and compression ration. Can this genuinely be the cause?

 

[Theon]

Not all of these motor kits are created equal.
If your looking for 60 Km/hr,
You may have to learn a lot about engines or try this.
http://screamingroo.com/online-store/category/engines/

 

[StanlyManly]

Not all of these motor kits are created equal.
If your looking for 60 Km/hr,
You may have to learn a lot about engines or try this.
http://screamingroo.com/online-store/category/engines/

Aren't they generally supposed to go a lot faster than 30km/h?? I can go this fast on my bicycle!!

I'm not looking at buying a new motor since I just bought this one!

 

[Henshooter]

What size rear sprocket do you run ?

Is it still in breakin period ?

A cheap and easy bolt on enhancer for performance would have to be a 36t sprocket , the increase in speed does cost some in hill climb ability but the overall speed will increase IMHO , I run a 32t which some have said might be a tad tall for a chinagirl but my average cruising speed is 60kph ( yes I said average the actual speed varies from 60 to 70 depending on conditions ) with no porting or other performance parts , I've also had several people tell me my cruiser is quieter than normal which is a bonus in my area.

The pickup to WOT is remarkably smooth also but the initial starting of the motor and warmup takes a few seconds more , but to start I've got to maintain around 10 kph or the motor just doesn't have the kick to get her started

Give one a go and tell us your progress

Regards Henshooten

 

[Greg58]

One of the easiest improvements is a free flowing exhaust, if you modify the pipe to flow better it will help your speed. It has on every one I've done, no matter if it were a 48cc or 66cc.

 

[2door]

As Henshooter asked, what is your rear sprocket size/tooth count?

If you cleaned the exhaust did you remove it from the engine? If so did you happen to look at the exhaust port on the cylinder? I've seen them more than half plugged with carbon residue from running 16:1 fuel/oil ratio.

You said you're running now with a 50:1 oil ratio. Is that recommended by the oil manufacturer? If not you're a little oil starved and with that much less oil per unit of gasoline you have a rich fuel to air mix. I'd expect that your engine is four stroking something fierce. When you reduce the oil content of your mix you effectively increase the fuel to air mix. That will require some experimentation with jet size to lean out the fuel/air charge.

Before you do that you can test this theory by mixing up a batch of fuel using a good air cooled 2 stroke oil at a 32:1 ratio. Drain your tank and try running with the slightly higher oil ratio and see how the engine performs. Let us know what you find and answer the questions we've asked.

Tom

 

[StanlyManly]

One of the easiest improvements is a free flowing exhaust, if you modify the pipe to flow better it will help your speed. It has on every one I've done, no matter if it were a 48cc or 66cc.

Okay, so forgive me for my ignorance on the name of the parts, but should I remove the baffle, and cut off the narrow metal rod that sticks in to the exhaust, or should I drill some holes or something? Can I assume this will make it louder?

One thing I'd like to say is that when I removed my baffle completely and took it for a ride, it improved speed a little, but not much. Is this different to making the exhaust more free flowing? Because I would assume having the baffle off would provide for the fastest possible speed out of the exhaust.

 

[StanlyManly]

What size rear sprocket do you run ?

Is it still in breakin period ?

A cheap and easy bolt on enhancer for performance would have to be a 36t sprocket

I run the stock 44T one.

No, it's been broken in with a 16:1 fuel ratio, and about 100km, on a easy speed.

Would you be able to link me a to one of those bolt on sprockets? That should be nice, since this 44T one was a PAIN IN THE ASS to get on! I live in a fairly flat area, so hills aren't my worry.

 

[StanlyManly]

As Henshooter asked, what is your rear sprocket size/tooth count?

If you cleaned the exhaust did you remove it from the engine? If so did you happen to look at the exhaust port on the cylinder? I've seen them more than half plugged with carbon residue from running 16:1 fuel/oil ratio.

You said you're running now with a 50:1 oil ratio. Is that recommended by the oil manufacturer? If not you're a little oil starved and with that much less oil per unit of gasoline you have a rich fuel to air mix. I'd expect that your engine is four stroking something fierce. When you reduce the oil content of your mix you effectively increase the fuel to air mix. That will require some experimentation with jet size to lean out the fuel/air charge.

Before you do that you can test this theory by mixing up a batch of fuel using a good air cooled 2 stroke oil at a 32:1 ratio. Drain your tank and try running with the slightly higher oil ratio and see how the engine performs. Let us know what you find and answer the questions we've asked.

My rear sprocket is 44T.

I did take the exhaust off when I cleaned it, but didn't check the exhaust port on the cylinder. I'll do that tonight. Can you recommend a better way to clean my exhaust? Possibly with a degreaser? Because I'm worried there might be some exhaust packing in there - I changed my mind when it didn't improve sound, so i took it out, but some might have gotten stuck.

Well I ran it at 32:1 for about a tank, and I noticed no improvement! I was actually told by a bloke on Screaming Roo's forum to use 50:1. What do you think? I'll have to play with the C-clip to get it going right, but I'll look for carbon build-up in the exhaust port.

 

[2door]

Keep in mind that the clip on the needle only effects fuel flow up to about 3/4 throttle. Anything above that the jet orifice size determines fuel flow. Moving the clip won't have any impact on wide open throttle, WOT, performance. It only controls low and mid range mixture.

Tom

 

[maniac57]

Most china kits are far too rich from the factory.
Mine required jetting down three sizes to get right but all are different.
I soldered and redrilled my own jets since the ones you buy are all over the place on actual size, regardless of marking. Using a wire gauge drill bit set gives better control of actual size.
I had three marked 66 and all three were different.
One easy way to check if you're too rich is to turn off the fuel and ride till it quits. If it speeds up and runs great right before it quits, drop the jetting size.

 

[StanlyManly]

Surely, if I bought some high quality jets I wouldn't have that problem! What about a new carb? So you recommend redrilling the current one? I'm nowhere near good enough to do that, I think I might have to stick to buying some!

OK I get your tip. So if it speeds up, smaller jet.... then I can assume this will give me more power! I'll buy some new jets now.

Most china kits are far too rich from the factory.
Mine required jetting down three sizes to get right but all are different.
I soldered and redrilled my own jets since the ones you buy are all over the place on actual size, regardless of marking. Using a wire gauge drill bit set gives better control of actual size.
I had three marked 66 and all three were different.
One easy way to check if you're too rich is to turn off the fuel and ride till it quits. If it speeds up and runs great right before it quits, drop the jetting size.

 

[Greg58]

A lot of the stock pipes are real restrictive, on one of my pipes I added another stinger or pipe to the end cap. It helped a lot and is not that loud.

http://motorbicycling.com/album.php?albumid=259&pictureid=1611

 

[Henshooter]

I run the stock 44T one.

No, it's been broken in with a 16:1 fuel ratio, and about 100km, on a easy speed.

Would you be able to link me a to one of those bolt on sprockets? That should be nice, since this 44T one was a PAIN IN THE ASS to get on! I live in a fairly flat area, so hills aren't my worry.

Unfortunately I can't post links with my iPad but here's a pic of the eBay listing ,just be sure you tell them the tooth size upon ordering , pretty cheap mod too if you ask me

As for the sprocket being a pain in the backside I've heard around some use a small bit of epoxy to line up the sprocket correctly and then tighten it up ,making sure you do this in a star pattern or it will misalign ,there is also a hub adaptor you can get from one of the members here ,I'm not sure who or where but I'm sure one of the other members will point you in the right direction

Regards Hens

 

[StanlyManly]

With my knowledge and tools, the best I could do is probably drill another hole in the end. That should do a decent job too, right?

A lot of the stock pipes are real restrictive, on one of pipes I added another stinger or pipe to the end cap. It helped a lot and is not that loud.

http://motorbicycling.com/album.php?albumid=259&pictureid=1611

To Henshooter... that's a cheap mod and it'll definitely add some speed. I thought you mean it would be an easier bolt on sprocket since these things are such a pain to put on! But I'll definitely grab one of these.... it'll add some good speed, and maybe with all these small modifications I can get some nice speed!

 

[crassius]

while checking things, be sure to take air filter off and look at the slide to see if full throttle lifts it all the way up