Author Topic: Crazy digital mutimeter.  (Read 540 times)

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Offline husker

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Crazy digital mutimeter.
« on: January 16, 2018, 02:01:23 PM »
Happy New Year Everyone! When I tried to check voltage on my 350 running verses not running the voltage reading would be all over the scale when it was running. Then I discovered that I didn't even have to hook it up and it would do the same thing just had to get within 2 feet of the bike. Tried it with another digital meter and it did the same thing.  Started a Honda up and that had no effect on the meters.  Haven't tried an analog meter. It does keep the battery charged up but what is going on?........Rod
1968 Bridgestone GTR350,  1971 Kawasaki A7SS, 1983 KZ750 LTD

Offline czmike

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Re: Crazy digital mutimeter.
« Reply #1 on: January 22, 2018, 06:40:13 PM »
Hi Rod,

All electronic devices, especially those employing digital techniques, are highly likely to suffer abnormal operation when operating close to a running, spark-ignition engine. The radiated electrical energy from an operating ignition system can be very strong and it covers a wide frequency range. It will disturb the normal operation of meters, timing lights and even the electronic ignition that is producing the spark - if one is fitted. Turn on an AM radio (off station) while your bike is running and you will see, or rather hear, what I mean. Actually experts use this very technique to diagnose intermittent misfires in engines. It often answers that thorny question - "Is it ignition or carburetor?" (almost always ignition in my experience).

While most electronic equipment manufacturers include design features to limit the impact of external interference some don't try at all.
It is always best to try to minimize the troublesome radiated signal at its source anyway.
With so many electrical devices around these days vehicle ignition systems are fitted with devices at manufacture to reduce this problem.
Modern vehicles are all fitted with suppressor-type spark plugs (resistor plugs) and suppressor-type spark plug wires which together dramatically reduce radiated interference. Fitting these to your bike will stop your problem I expect. The NGK R range of spark plugs are very good and spiral-wound spark plug wires are the best to get (MSD or Moroso's Blue Max are both super). Even though our spark plug leads are very short replacing them with these special wires will help reduce the problem with your multimeter.

There is a slight loss of spark energy when these devices are fitted (they are mandatory for electronic ignitions!) but this loss is small and you will not notice the difference with a properly working battery & coil ignition system as employed on our GTR's. Magneto ignitions (e.g. Bridgestone 90's, etc.) may not work so well with suppressor devices fitted due to this loss.

Hope this helps Rod - sorry for so many words but this subject is huge & complex (just like 2 stroke engines!).


Best Regards,

Mike (in sunny Australia)
« Last Edit: January 22, 2018, 06:49:08 PM by czmike »

Offline husker

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Re: Crazy digital mutimeter.
« Reply #2 on: January 28, 2018, 10:27:10 AM »
Thanks for the explanation Mike, the Honda (CX650) must have a lot better shielding.
1968 Bridgestone GTR350,  1971 Kawasaki A7SS, 1983 KZ750 LTD

Offline czmike

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Re: Crazy digital mutimeter.
« Reply #3 on: January 28, 2018, 05:15:36 PM »
No Worries Rod,

If the Honda CX 650 has points triggered ignition then it probably has a Suppressor Type spark plug connector fitted and/or suppressed high tension leads. Suppressed plug caps are another method of reducing the radiated interference from the ignition system but they are less reliable than resistor type spark plugs in the long term. My recommendation is to use only R type spark plugs as the suppressor (I have a belief that using these makes a two stroke engine run nicer anyway).

There is no "shielding" as such (shielding implies a covering-up or physical protection of something).
Suppressor strategy is to add resistance to the system so the spark voltage doesn't ramp up quite so fast as it would without the resistance. Still pretty fast though.

Regards,

Mike
« Last Edit: January 28, 2018, 05:29:34 PM by czmike »

 


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