speedometer won't work w/ engine on

[crowvise]

Had bought a $20 wallyworld "bell" speedometer. read fine w/o motor on. W/ motor on reads 56-62mph at comparable 12-15mph motor off reading. my 1st guess is the magneto and/or cdi was affecting it. 2nd guess vibration was a factor. Any similar experiences? Whats a decent, cheap speedometer. will the digital ones work on these bikes?

 

[Stan4d]

Is this a wireless speedo you are talking about? There is usually too much interferance for those, though some have found the sweet spot where it works.

 

[crowvise]

yep it is wireless. I returned it. But still want to know.
Still 56-61mph pre break-in would have made my motor the

 

[AussieSteve]

You'll have trouble with a lot of speedos, even wired ones. Avoid the 'Sunding' brand from eBay, they reset every time the engine is started.
I use a Cateye wired speedo now and have had no problems at all.
Many people recommend the Schwinn speedos, too.

 

[TOTAL CARNAGE]

I have two of the Schwinn speedos. Both the same. One works fine, one resets every time the engine is started.
With the one that resets, I have moved it to the rear wheel, well away from any rf noise.....no good. Made the wire shorter.....nope. Shielded the wire and speedo.... .......saved it for a bike WITHOUT a motor....Yea!
I guess you just have to get lucky. Some work, some won't. Even within the same brand.

 

[GearNut]

The ignition system creates EMI also known as RFI. This will affect all kinds of electronic gizmos ranging from bicycle speedos', radios, cel phones, cheap digital cameras, ect.
As you ride your bike down the road it can easily affect the radios in the cars that you ride by. If they are listening to broadcast radio and not a CD or MP3 player they will hear a buzzing in the speakers at the same frequency as your spark plug is firing.
http://en.wikipedia.org/wiki/EM_interference

 

[RedBaronX]

I bought one of the retro looking ones, and I can't get the danged thing to fit on my hub AND get the wheel back into the fork... I am generally a smart person, but I can't stand being thwarted by a really basic piece of machinery...

 

[AussieSteve]

At least if you do get it to fit, you won't have interference problems with a mechanical type.

Like you, TOTAL CARNAGE, I tried shielded leads etc with the 'Sunding' speedo, but could never get rid of the problem. Sounds like it's the luck of the draw with Schwinn speedos too.
With a wired speedo, running the wire down the front brake cable helps. That keeps it further away from everything.

 

[Bob Mac]

Try the resistor plug. That's all mine needed. I was ready to junk it until then

 

[GearNut]

Resistor wires, resistor spark plug caps and resistor plugs were all invented to reduce the effects of EMI/ RFI.
Some ignition systems are designed to use all of the above, but I think it is overkill.
I also would not recommend trying all of them at once on these cheap CDI ignitions.