MOPED ARMY

That kit and pipe probably are not hitting that high rpm. Is your tach adjusted right? Check out moped toolbox you can put in your gearing and speed to get a aprox rpm.

I had a similar setup with a shitty crank and literally blew up my motor, the crank blew through the cases at aprox 10,500 rpm at around 380 degrees.

So yes, on a stock crank you are going to want to put that 17 up front again at least until you can validate your tach or rebuild your bottom end. If you stay under 8500 rpm you are fine. (edited)

Yah that’s what I was thinking but it’s definitely set on 1p1r….

Just seems nuts that it’s spinning that fast…think it’s getting interference from a non resister plug?

Also idle is sitting at around 1100 which seems kinda right

I’ve used Marty’s garage for gear ratios and if I was pulling those kinda Roma I should be doing like 50…which I know it isn’t

Thx

My hogged out polini spins 5 digits 1/2 throttle boi

Yeah, I like the pull with the 15/45 but top end could be better…I’m thinking it might hit 40+ but when I saw those rpm’s climbing like that I was like “whoa “!!!

Like I said I had a 17/45 on it and it was pretty slow off the line and on hills…top speed was pretty fun tho’ lol

So down the road I guess a new crank would be prudent (maybe this winter!)

When the bushing crank goes bye bye what can I expect? Busted crank or just no go no mo?

Thx!

What could possibly be wrong with the tach?

Just a shitty one?

If the pipe won’t let it rev out that much should I not be concerned?

Marty’s garage seems about right as far as the gearing/speed seems so the revs should be pretty spot on too correct?

Thx

I don’t know what magic number you’re talking about but for a techno circuit pipe 16x45 Gears is not the magic number

That’s over 10,200 RPM for 46mph and actually from seeing a running a tachometer it’s more like 10.5k to get 46mph. I never got 10.5k rpm out of a circuit pipe with a simple 70cc kit bing setup.

A circuit pipe is about 8.5K so 17×40 gears is the magic number for 45-47mph and even 16x40 is about 42-43mph, They both are pretty close and you basically only need thick springs in your clutch, nothing fancy like higher rpm pipes need.

The tecno circuit pipe is so torquey that you could go just as fast as Boss or bullet pipes with lower RPM even though it doesn’t feel as fast as those pipes because even though it’s not screaming as much it is just as fast.

I did dozens of 70cc kits with 14-15mm bing and circuit pipes, Like I said with its lower rpm power it’s a crank saver and it’s perfect for a stock crank engine whereas a bullet or Boss pipe can ruin it (if you’re tuned correctly for those pipes to rev out) as well as needing a better tuned clutch to get into the higher powerband they have

I like 17*40 with a 70 kit,bing and circuit. tire size will also affect rpms if I'm not mistaken. Here is some screen shots from the excel sheet I use for gearing

Just. curious

What tach iis everything be using?

Any formula?

Thx

Tecno estoril or circuit? The estoril will over run to just over 10k, I don't see where it says that it's a circuit but yeah that's wrong if so.

Oh sorry yeah nevermind then, you're good, 16*40, stock crank, tune clutch. Ken roff special. Don't fly too close to the sun melt your crank bushing like Icarus.

Use the puch gearing/rpm calculator .

GPS your top speed, then check that on the gearing chart to determine what rpm you are hitting. Doubtful you are hitting 12K.

And yes I would recommend a Rito needle bearing crank if you plan on running 9k or more for very long.

Regarding the tecno circuit pipe topping around 8.5K rpms....then please explain why mine revs out to 9,400 rpms according to Marty's calculator. 70cc piston port treats kit on e50 1978 Newport, no case match, tecno circuit pipe, 12mm bing with modified stock airbox, grandpas 15mm intake, 64 jet single ring needle clip on 2nd leanest notch, 15X45 gearing stock wheels/rims. 38-39 mph verified by phone speedometer gps on flat roads. Running temp gauge temps mostly in mid 200s sometimes very low 300s on sustained WOT runs for 5+ miles (between 305 and 335 degrees tops even after bombing up a long 1/2 mile hill). So the circuit pipe can hit 9,400 rpms on flat roads and remember I'm rocking only a 12mm bing with modded stock airbox