Misfire at idle only!

[redtrummy]

If it is an idle/pilot jet a good dose of redex could cure it. I started to go down the plug route - changed the front - no change - had little petrol in the tank so banged a a good dollop of Redex in and over a couple of weeks it was running as sweet as a nut. (must get round to changing the rear plug sometime)

[SV650rules]

There is probably a 5000 ohm resistor ( if there is an 'R' in plug number ) and that can fail. The resistor is there to reduce radiated electrical interference ( making whistles and crackles on radios ). More likely to fail on cheap plugs with dodgy provenance, but can fail on rare occasions even on proper plugs. If there is a resistor in the plug then there should not be one in plug cap...

[gadget]

Originally Posted by SV650rules

There is probably a 5000 ohm resistor ( if there is an 'R' in plug number ) and that can fail. The resistor is there to reduce radiated electrical interference ( making whistles and crackles on radios ). More likely to fail on cheap plugs with dodgy provenance, but can fail on rare occasions even on proper plugs. If there is a resistor in the plug then there should not be one in plug cap...

I use the standard CR8E plug so no 'R' in the code. They are only a year old and not done 1500 miles! Might change them as a matter of course anyway.

[gadget]

Originally Posted by redtrummy

If it is an idle/pilot jet a good dose of redex could cure it. I started to go down the plug route - changed the front - no change - had little petrol in the tank so banged a a good dollop of Redex in and over a couple of weeks it was running as sweet as a nut. (must get round to changing the rear plug sometime)

I was hoping to get the chokes done today, fill the tank with fresh fuel and a big dose of redex and take it for a good long run but ran out of time, so as soon as I get a few hours spare and good weather permitting I'll take it out for a blast and see what that does before getting into electrics or carb stripping.

[SV650rules]

Originally Posted by gadget

I use the standard CR8E plug so no 'R' in the code. They are only a year old and not done 1500 miles! Might change them as a matter of course anyway.

CR8E - no you are right, no R in the code

[R1ffR4ff]

Originally Posted by gadget

I use the standard CR8E plug so no 'R' in the code. They are only a year old and not done 1500 miles! Might change them as a matter of course anyway.

There is an R in your code. The 5k ohm resistor in the plugs is there to stop Back EMF not radio interference affecting the ignition timing in CDI/Electronic ignition systems. Another one is in the Plug caps which may be the cause.

Have a read here,


https://cx500.000webhostapp.com/SV65..._And_Caps.html

[SV650rules]

https://www.ngk.com/what-is-a-resistor-spark-plug

[R1ffR4ff]

Originally Posted by SV650rules

https://www.ngk.com/what-is-a-resistor-spark-plug

Although the RFI is created this is not the issue with interference with the ignition system. It's the Back Electromotive Force created that caused the problem.

Capacitors are used to suppress noise in AM Radio receivers

[SV650rules]

So what used to cause 'snow' on old CRT tv sets when a car or bike went past...

The energy that creates the spark starts with the magnetic ( ferrous core ) of coil being energised by 12 volts ( dwell time ), if you left coil connected to 12 volts you would not get a spark, just the coil would get warm, the current flowing limited only by DC resistance of primary coil of ignition coil - the magic happens when the current flowing in primary is interrupted and the magnetic field collapses. The energy stored in magnetic core now feeds back into the windings of the coil, it cannot escape via the primary winding as it it open circuit so voltage continues to rise until the voltage breaks over the gap in spark plug, the 5000 ohm actually makes this harder, but limits energy radiated to environment. So the spark is actually caused by back EMF from a collapsing magnetic field. How the transistors or switching device in primary circuit is protected is down to design of electronics ( the old style systems with mechanical 'points' used a capacitor in parallel with points to reduce spark erosion of the points material ).

But what would NGK know, they only make the plugs.. EMC regulation are more concerned with how emissions from a device affect other equipment than how they affect the equipment itself, which is ultimately down to good design.

https://ieeexplore.ieee.org/document/4090839

[R1ffR4ff]

Originally Posted by SV650rules

But what would NGK know, they only make the plugs.. EMC regulation are more concerned with how emissions from a device affect other equipment than how they affect the equipment itself, which is ultimately down to good design.

I'm lucky. My SV doesn't have a TV or AM radio fitted LOL

I'm not arguing that RFI interfered with older AM radios and or CRT TVs but it wasn't the resistors that stopped this in Automotive vehicles but the capacitors(Automotive term<Condenser). These were usually fitted inside the old Distributer caps and also some vehicles had them fitted on other areas as well to aid Noise suppression and helped prevent coil and points burn.


If you don't believe me do as I've just done. I have a small pocket AM/FM radio I used when contracting and also sometimes in my garage. Start your bike up and find an AM station and hold it near the Front cylinder and you will hear the Radio Interference. This proves that neither of the two resistors in the system(Spark Plug Cap and Spark Plug)suppress Radio interference as it's not their function.

Do the same with an FM station and you won't hear any as FM radio is not affected by Automotive RFI because it does not affect Frequency Modulation only Amplitude Modulation in this instance.

HTH