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[jefrs]

Ooops, the NGK BPR6ES also has a resistor (the 'R', Bosch also use that 'R') and does not need a suppressor cap, it must be the Champion without internal suppression.


Not a bad YouTube video but I'm a little leery of using anti-sieze on plug threads since ejecting one having used it. The copper compound creates an electrolytic reaction between the steel plug and the aluminium head, just add electricity, in this case lots of it and you get a sacrificial anode and the threads disappear from the aluminium, oops. Cleaning the plug hole is a very good idea before pulling the plug. That squish washer on a spark plug sets the torque properly if used correctly but it only has a few goes in it, they used to sell replacement washers but now we toss the plug. His 'normal' colour looks sooty to me, not right, see the Haynes joke book.

[jefrs]

Did I say copper, we tend to use copper-ease but that one looked like moly-slip and the same thing happens with molybdenum (which I spelt all by myself), something to do with redox potentials but college chemistry was in the last millennium.

[ric]

You only need 5Kohms of total suppression with the modern ignition system to provide the electronics with adequate protection from stray RFI.
The standard plug cap is 5K and the supressed Bosch is also meant to be 5K. Basically twice as much resistance as required. I opted for an unsuppressed NGK plug cap paired to a supressed NGK plug almost as soon as the bike got back from the showroom and have no ignition problems whatsoever.

[jefrs]

My OEM metal HT cap literally fell off the HT lead. There was evidence of spark erosion on the top of the plug, that caused the plug to track down the insulator, poor spark and foul, so both binned PDQ. Current plug is the BPR

[jefrs]

I do have a rev counter (the Smiths tacho which doesn't fit the C5 but does on a handlebar clamp, a Brooks saddle pin 7/8 job) and the book of words does say one should only monkey with the idle speed by about 200rpm either way, so I've increased it by about 500rpm. These bikes tend to be very variable one to the next in what they need like feeding cats. Mine idles at 1100, yours might like 950.

The auto decompressor is supposed to operate below 300rpm but listening to mine going click as it drops out after starting it's about 700rpm. So if I drop the idle too far, the decompressor cuts in and stalls the motor.

[Thack]

jefrs writes: "The auto decompressor is supposed to operate below 300rpm but listening to mine going click as it drops out after starting it's about 700rpm. So if I drop the idle too far, the decompressor cuts in and stalls the motor."



Actually, it's 350rpm, and this is camshaft rpm, not crankshaft rpm. So your observation of 700 (crank) rpm is spot on.



By the way, it's not entirely clear why the decompressor cutting in would stall the motor. After all, the engine is designed to start with the decompressor engaged, so surely it must also run in that state. Mine did, by the way, until I eliminated the god-forsaken piece of junk.

[jefrs]

Thanks Thack, that explains it (if all else fails, read the manual, "...cam rotation will be under 350rpm"). So when I set the idle to maybe 800rpm of course it drops occasionally and the decomp kills it at 700.

[jefrs]

On some old motors, the only way of stopping them was opening the decompressor, it will kill an engine. I think the point is you can't kick it up to 700rpm (crank) but as soon as the engine fires it will go over that. On start up I do hear a ticking noise for a few moments, I assume the valve is still lifted but not full help open. The current C5 is 8.5:1 which is around where a kick-back hurts, so it does need the decomp, my old boots have steel plates in the instep

[Trev]

Interesting thread, thanks to all participating. I too sometimes hear a ticking sound for a second or two after atartup and have assumed hydraulic valves getting up to pressure, I've had my EFI for 3 years/7k miles and it's always done and still seems ok. Any sure fire knowledge out there on what it actually is?
Also interesting to hear about decomp coing in at low revs, I notice if i take a real hefty launch on the kickstart (a la my old 2 stroke enduros) often the kick start will go to zero resistance which is a bit jarring on the old knee joint! The nack I use is a long, consistent swing and this usually works, if not after a few attempts then prod the button ; )

[Thack]

jefrs writes: "On some old motors, the only way of stopping them was opening the decompressor, it will kill an engine. I think the point is you can't kick it up to 700rpm (crank) but as soon as the engine fires it will go over that."



But those decompressors aren't the same as the one on our Bullets. As you say, they were a valve which totally decompressed the combustion chamber. The one on our Bullet holds the exhaust valve open for a bit longer, so really it's a "low compression" device.



But as I say - if it will fire with the auto-decomp in operation (which it must, to start), how can the auto-decomp possibly make the motor stop?