Planet Minis

ducatilover

I was asking myself this question the other day: Why cant the stock z50 hit a top speed similar to a ysr50 or an rs50 or even some pocket bikes?

Im some of you mechanicaly inteligent people can shed some light to this. The question came up as I was thinking about my very first motorcycle (ysr50). I used to hit 45mph and with jetting and exhaust I could do close to 55mph.

nielspbr

Simple, the engine is designed for endurance and economy, not for top speed.
See honda (super)cub 50.

1TrikZB

For the same displacement, 2-stroke usually has more hp than a 4 stroke.

peace,
bobbyV

mexicanyella

Sort of in the same vein, how fast have people found their stock Z50s to be? Is there much difference between the K0-K2 group, the K3-on group, and the Z50R?

My K2 could do 23-25 mph with a 200 lb. guy on it on level ground, but that was with a tiller tire on the back, a lawnmower air filter and lots of hours on the engine. Maybe not the ideal top speed setup, in other words. My memories of brief rides on older softail Z50s suggest that the later ones had a bit more power and speed (?)

arlindsay1992

Stock Z50R can do about 45 with gearing and intake mods. That's about all it can pull. Two strokes are lighter and more powerful so that's why they go faster.

TankTheory

My '95 z50r did 30 stock and im 140lbs. I just put a 15t on the front and am yet to get someone to clock me with that small change.

arlindsay1992-what gear combo are you running/what intake mods have you made? Ported out intake, head and carb?

tmas

High speed record guy thread.
tmas

http://www.planetminis.com/f14/here-...lan-32818.html

Branyers

That's a great top speed for a 50. 45mph, absolute tops, is all I can remember hitting on my stock 70, and this is with no wind and a slight decline if anything. Never tried lightening it or getting in the fetal position though.

Nice thing about the stock bikes is that you can run them all day long WFO without precaution.

arlindsay1992

I had a stock 1984 Z50R with a TB 3 plate manual clutch. The TB primary gears had the same ratio as the stock 1984 parts. Intake mods would mean take out the intake straw, backfire plate, and choke, then adjust air screw and needle accordingly until performance is best. On a stock bike you'll notice a tiny more pep from the intake mods. Nothing to win a race but still noticeable. Anyway, 14/37 gearing will give you 43 and I think on a good day with a tail wind you could pull 45 with 15/37 gearing in fetal position, with a light bike and rider. But realistically, the bike will hold a constant 39 or 40 in normal riding position at WOT. And yes you can hold it there forever. I rode for 10 minutes at WOT 40mph on my stock bike a while ago. Never had a problem. The stock motors are indestructible. I was probably holding 10,000 RPM the whole time.

Z

A brand new Honda Monkey out of the box (13/31 gearing) after break in with a manual clutch from the factory and a 4 speed will only do 38mph out of the box.

Some of your numbers aren't making sense to me.

A 14/37, with a TB manual clutch, 3.5X8 tires and the stock gearbox would need to push over 11,000 rpms WOT to hit 43mph. A stock 50 can't sustain 11,000 rpms WOT on a level surface, let alone sustain 10,000 rpms.

With the above combo with a 15/37, to hit 45mph, you'd need to sustain 11,000 rpms.

I've seen 72cc bikes go that fast, but not the 50cc bikes.

You must live on a large hill...

arlindsay1992

I double checked with the gear ratio/speed calculator on the Honda 50 site and yes, what you said is true. I honestly have no idea how I got the the numbers I did. I am forced to assume that the GPS was wrong (not likely) or that there is some other factor I am overlooking. I am just as baffled as you are but I can assure you that I didn't exaggerate any numbers or specs. I checked what I posted and can find no typos.

X7rocks

some pocketbike 4 stroke 50s come with basically the same stuff as a z50 but usualy have much larger ports and come with larger gearings like 14 front 38 to 35 rear sprockets
and if there semis or automatics they have 4 gears from the factory to play with
and since the 50cc pocketbikes arent ment for performance there more for economy and rideing around so they basically have the same guality as one of the 50s you ride but what i noticed for the pocketbikes the higher you go in size of the motor the more durability it will lack soon thats why some of them never go above 125cc only 107cc

gstegman

Check your GPS to make sure it is set to statuate miles and not knots. Just a thought (or have a chase car clock you).

firepower354

Apples & aardvarks

__________________
If it has my name on it I did it;)

FirepowerMinis.com
Custom FPM parts and engines.
Parts and service for all makes.
Honda Trail Bikes parts and accessories.
Pitster/Piranha/Thumpstar bikes, parts, engines and accessories.

mexicanyella

I just looked up my combination in that gear ratio calculator in the tech resources section (stock 6V Z50, three-speed auto, 12/35 sprockets, 4.00x8 tire) and came up with 25 mph = about 6750 rpm.

That seems about right; when I checked my speed against a street radar trailer years ago it was fluctuating between 23-24, and when I hooked up a little "tiny-tach" inductive tachometer later on I could only pull about 6800 rpm on flat ground, flat-out, with the tiller tire on there, which is probably a little tall for a 4.00x8. On a downhill, throttle pinned, I just barely saw 8500, which worked out to 31-32 mph.

Figuring my weight (substantial) and the rolling resistance (high) and engine condition (probably never rebuilt in decades) and probably the beginnings of the air leak from the stripped manifold bolt I discovered, that's probably to be expected and I'm lucky I didn't burn a valve or hole a piston.

I've since swapped the other motor I have in while I helicoil my manifold bolt holes (it's also a stock worn old 6V motor) and yep, they run better without air leaks. It feels more free-revving. I plan to put the tiny-tach back on for another test session this week.

I've got 14/35 sprockets on there now and a real rear tire, and it feels faster but not quite powerful enough for the gearing.

Time to freshen that motor up, and enlarge it a bit.

Thanks for all the info; didn't realize mine was THAT tired.

mexicanyella

Just back from a test run with the second motor, 12/35 gearing, no air leak, tiny-tach reinstalled and freshly greased/adjusted steering head bearings.

It's running better. On flat ground, throttle pinned, it was hitting a max of 7370 rpm--about 28 mph--and pulling nearly every paved hill around here in 3rd gear, dropping to about 4350 rpm by the time I reached the crest of the longer/steeper ones but still pulling.

It's definitely happier with the 12/35 gearing than it was with the 14/35, at least with this stock tired power level. It's definitely more fun with a limited top speed but running crisply and eagerly. 2-3 more mph isn't worth dogging out on all the hills and having to shift down to 2nd.

jrotten

45 mph seems awful fast,unless engine is modded.25 mph seems more reasonable for a z50

LoudFastUgly

My resto project 84 CR60R made over 13HP, no idea about top speed, but it'd lift the front tire with me on it (210 Lbs) in 2nd.

An absolute weapon, and a darned shame they were only available in North America for two years.

arlindsay1992

I got 43. I think 45 is possible with stock parts and gearing.

jrotten

yes,but the cr60 is like comparing apples to oranges,racebike-beginner bike,2 stroke-4stroke