Stock Tachometer Inaccuracies

[Deleted]

As we all know most speedos on these gy6 scooters are about 15% to 20% optimistic as a general rule. Yesterday I was riding a 50cc that I had BBKed and more. While I was riding I noticed the tach was showing 3k rpm @ idle and over 12k @ full throttle road speed.

My curiosity was aroused about the tach inaccuracies and what others might have seen as a rule of them. Is it the typical 15% to 20& we see in speedos or is it more?

btw.. the tach only shows to 10k rpm, so my statement is a WAG rpm based on needle position.

[90GTVert]

None of my scooters ever had a stock tach so I'm not sure what's common. Idle is usually more like 1500-200RPM. The GY6 50 more commonly likes to rev out around 7500-8500RPM, but can go higher. Sounds like your tach is more than 15-20% off, or your idle is set high and you need an upgear or have the wrong rollers or worn belt or something like that. You should know it if it's hitting 12000RPM from the sound of the engine. It won't sound like everyone elses scooter chugging along at ~8000RPM and unless you've done a lot of work it shouldn't be making much power at that RPM.

[Sitticuss]

I've only had one with a stock tach. It seemed to be pretty accurate. As accurate as an old school needle vs a digital

[Deleted]

Suppose the only real way to know is test it. If I can find enough time, I'll hook a couple different DMMs into it and then road test it to find out how far off this one is.

[90GTVert]

If you have a timing light that shows RPM it's real quick to check without that pesky math stuff.

[Deleted]

the issue is now moot- had it listed on CL, first person that called, rode it

returned grinning like a Cheshire cat and bought it

said he had never ridden a small scoot like it- paid full asking price-- no negotiation what so ever

had 5 more buyers lined up behind him