Ingition pistol rpm reading weird

Hello,

I have a strobo light with a rev counter in. Putting it to 2-stroke mode, it should read correct rpm (one spark each rev).
What I see is fluctuate reading between right and double the revs compared to what the bikes tachometer shows.
It changes erratic, on 1-4 it is from 2 times a second to "double spikes". On 2-3 its mostly double with spikes to the right rpm.
Is it a false reading of the strobo tool (e.g. sensor at the plug gets neighbors signal too) or false spark? How can I narrow it further down?
The Z650B is quite new to me. Points and ignition timing are adjusted to spec and looking well. 

Cheers
Joerg

Don't forget when you use a strobe light on a car with a distributor each lead only sparks every 720 degree's (camshaft turns at half engine speed) with a bike with dual output coils and a "lost spark" set up each lead sparks every 360 degrees (so double) depending on the strobe you have I'm not sure you will get an accurate tacho reading (does it have an option for 8 cylinders (twice as many sparks as a four cylinder in car world)

Hi,

I thought the 2-stroke setting would do it. One revolution - one spark per cylinder (combustion or lost) - one rev count.

Cheers
Joerg

Each cylinder only fires a power stroke every second revolution so it depends what your tacho is looking for

Fire - power stroke - exhaust stroke (one revolution)
          Induction stroke - compression stroke (second revolution)

Ok. Just put 3 + 4 spark plug out, ignition on and turned the crankshaft with the 17 wrench.
It does one spark per revolution on spark 4 and one on 3. So I think I am good with my spark frequency.

Is it normal that the points check bulb does not go out when I pass the F mark (point opens)?
It glows low and stays there until point closes again but isn't out. Cables to coil are connected, ignition is out, kill switch is on.
Repair manuals tell that it should go out.

Cheers
Joerg

 

wrote:

Ok. Just put 3 + 4 spark plug out, ignition on and turned the crankshaft with the 17 wrench.
It does one spark per revolution on spark 4 and one on 3. So I think I am good with my spark frequency. 

Is it normal that the points check bulb does not go out when I pass the F mark (point opens)?
It glows low and stays there until point closes again but isn't out. Cables to coil are connected, ignition is out, kill switch is on.
Repair manuals tell that it should go out. It won't go out completely straight away as the condenser is there to soften the switching action so the points don't burn up

Cheers
Joerg



 

Hi, 
I researched a bit on wasted spark concepts and learned that the combustion stroke has a much higher spark voltage compared to the exhaust stroke because of huge pressure differences. 10.000 vs 1000 volts is stated. 
So I assume that my RPM meter gets confused and detects the wasted spark sometimes and sometimes not and thus shows double/single  readings. Probably I need a better measuring device to tune my air screws to max rpm.

Cheers
Joerg

Use a gunson colourtune tool to set airscrews not rpm. It's not an expensive tool. 
With a colourtune you can get it accurate by actually seeing the mixture burn colour for each cylinder. 
Orange burn is rich, blue is lean. At approx 1800 rpm you want to see blue with a merest hint of orange. 

Yes, will do. I have already purchased the tool.

Cheers
Joerg

Following Warrens advise, I did the Colortune exercise today afternoon. It went well.
All four showed orange with some blue spots at idle with airscrew 1.5 out. Added another 8th or so out to get it more into blue.
Took her to a test drive, all fine, great trottle response.

Is there a description on what the test spark should show for my engine/carb at what rpm range? I only checked idle today.
Its a Z650B2 with a VM24SS, all stock.

Thanks to Wookie and Warren helping me out.

Cheers
Joerg

You can't use colourtune above about 2500 rpm with any safety.
The glass view point could break from rapidly repeated high compression and send shards out at high velocity above that. Dread to think what that could do to an eye if viewing when it broke. Safety first. 
Pilot circuit is approx up to 1/3 throttle. Main jet is upto about 2/3's. Needle valve is the last third. There is overlap between each circuit to ensure smooth throttle response. 
If you need to check mixture at higher than 2k rpm you need to do it by the plug chop method. If you decide to do this ensure you cut the engine whilst at that rpm and coast to a stop. Then check the plug colour.