Limiting top speed.

[Iovak]

I need to limit my 2 stroke,49cc motor to go around 15-20mph to meet local laws.How should i do it?

 

[Frankfort MB's]

I need to limit my 2 stroke,49cc motor to go around 15-20mph to meet local laws.How should i do it?

You don't have to limit it. Just don't go full throttle.

I've never had problems with meeting laws, most cops around me don't care

 

[bakaneko]

I mean check your speed as Frankfort suggest but if the police or DMV are really pressing you I would show them the engine specs and then show them the corresponding sprocket that would limit you to below 20 mph. This will probably be a 56T sprocket.

http://www.diygokarts.com/speed-calculator.html

Wheel diameter = 26"
Engine Max RPM = 6000
Teeth on Axle = 56T
Teeth on Cluth = 10T
Speed = 83 MPH!!!

But, there is an internal 4:1 gear reduction for 2-stroke China engines I think... so speed is 20.75 MPH. And, this is no load so with load I'm sure it is below 20 mph.

 

[Deleted member 12676]

without having some kind of electronic limiter in the CDI that cuts spark above a certain RPM it is not possible to do.
Limiting the intake or exhaust volume limits engine power, not speed. With a limiter of volume you could still go fast downhill.

 

[bakaneko]

Also, the reading on most motorized bicycle laws goes something like "cannot propel a X lb rider (180 in WI) faster than X mph (30 in WI) on a flat road with no wind." I am not sure if your local ordinance and laws reads similar but of course even with a 56T sprocket going downhill or with the wind you can go faster than 20 mph but on a flat road with no wind and if your 2-stroke engine max rpm is 6000 a 56T should not propel you faster than 20 mph. right?

 

[DanTheDIYGuy]

Also, the reading on most motorized bicycle laws goes something like "cannot propel a X lb rider (180 in WI) faster than X mph (30 in WI) on a flat road with no wind." I am not sure if your local ordinance and laws reads similar but of course even with a 56T sprocket going downhill or with the wind you can go faster than 20 mph but on a flat road with no wind and if your 2-stroke engine max rpm is 6000 a 56T should not propel you faster than 20 mph. right?

Sad that the government micromanages us like that eh?

 

[HeadSmess]

without having some kind of electronic limiter in the CDI that cuts spark above a certain RPM it is not possible to do.
Limiting the intake or exhaust volume limits engine power, not speed. With a limiter of volume you could still go fast downhill.

now that i agree with... hmmm... thinking how this could be implemented...

trigger voltage is charging a CR circuit, that is shunted with suitable zener, so once voltage across CR reaches certain level, thyristor is never triggered? im sure theres several ways to do it...

 

[Steve Best]

I need to limit my 2 stroke,49cc motor to go around 15-20mph to meet local laws.How should i do it?

A much longer intake or exhaust (like the PooPoo pipe) has this effect, but also increases power on hills below the max speed.
A restriction on the intake or exhaust such as an intake gasket with a smaller hole will have this effect too.
Combining a
1) long exhaust
2) a long intake
3) low gearing (56T sprocket)
4) an intake gasket with a hole sized to exactly limit speed
will give tractor like power on the hills and trails while not going over your speed limit.

Steve

 

[Frankenstein]

now that i agree with... hmmm... thinking how this could be implemented...

trigger voltage is charging a CR circuit, that is shunted with suitable zener, so once voltage across CR reaches certain level, thyristor is never triggered? im sure theres several ways to do it...

Why don't you help me with my battery problem thread, you know the powers you mess with.

 

[butre]

QUOTE="HeadSmess, post: 415041, member: 11023"]now that i agree with... hmmm... thinking how this could be implemented...

trigger voltage is charging a CR circuit, that is shunted with suitable zener, so once voltage across CR reaches certain level, thyristor is never triggered? im sure theres several ways to do it...[/QUOTE]
I'm no electrical engineer, but wouldn't something that limits the frequency do the job? I would think a low pass filter set at for example 160 Hz to limit at 9600 rpm would do the job.

alternatively, but a bit of a rube goldberg, does anyone make a tach with a shift light that will work on a single cylinder 2 stroke? hook the shift light output to a relay that cuts the spark and you've got an instant rev limiter.

first option is a soft cut, nice and easy on the motor. second is a hard cut, way more fun than a soft cut.