RGS Headache File

[Garry]

The problem.
One cylinder regularly cuts out and the rev counter starts to fluctuate or drops to 0.
I suspect it’s the central cylinder, as that’s where the rev counter signal comes from (?) It’s not constant, but happens regularly. This occurs every time the engine reaches operating temperature, after about 35 to 40 km.
I’ve replaced the ignition system (now Sachse), renewed the wiring from the coils to the ignition module, and replaced the coils, coil leads and spark plug caps (now red NGK caps and leads) as well as the spark plugs (originally NGK, now Champion N3C). I’ve connected the module directly to the battery to rule out the ignition switch and kill switch. Replaced the earth cable and sanded down all earth connections.
Replaced all brass carburettor parts and adjusted and synchronised the floats correctly.
The battery is fine. 12.3 V with the lights on and 14.5 V with them off, both when cold and warm. I’ve connected the alternator wires directly, no longer via the light switch.
It runs perfectly until I’ve ridden for 35 to 40 km, alternating between gentle and fast riding.
I’m running out of ideas.
What else can I try? Does anyone have any suggestions?

 

[Garry]

I’ve just realised that if I connect the module directly to the battery, the kill switch still works… after all, the ignition coils are powered via the ignition switch through the kill switch… so let’s see how I can get round that.
(Thanks, AI Google )

 

[Rob]

How frustrating.
Yes, as standard the centre coil provides the revcounter signal. So its flickering indicates that the coil supply/function is impaired.
Did the problem occur with the original BTZ ignition as well as the Sasche?
Another question. Where did you measure 12.3v and at what revs?

 

[Garry]

Measured on the battery at 3 to 4000 rpm.
It already had a DMC2 ignition system fitted. Same problem

 

[The Sock]

Have you checked the ignition trigger cables?
Are they electrical or optical?

 

[Rob]

Measured on the battery at 3 to 4000 rpm.
It already had a DMC2 ignition system fitted. Same problem

That's low for an RGS. I would expect little change lights off -> on at those revs .... certainly more than 14v. But regardless, DMC and Sasche will work happily at 12.3v. I wonder if you have a failing / failed reg/rect.

To bypass that possible issue, you need to disconnect the coil +12v supply from the kill switch (orange/white) and temporarily wire coils direct to battery. Bit of a PITA to stop the engine so leave the connection accessible! There is a connection you can break - leaves the kill switch supplied both sides but ignition off will fix that.

Sensor question by Hamish (The Sock) is a good one

 

[hooksey]

Try a new battery, cells do collapse & voltage drops in & out. The RG series do produce weird harmonics, especially with shagged out engine mounts!

 

[Garry]

Have you checked the ignition trigger cables?
Are they electrical or optical?

New Sachse ignition.

 

[Rob]

And just to clarify, you experienced the exact same issue with the DMC2?

 

[Garry]

And just to clarify, you experienced the exact same issue with the DMC2?

Yes

 

[Garry]

I’ve just done a test drive after connecting the ignition coils directly to the battery – unfortunately, no improvement…
When I come off the motorway after driving at 5000 rpm for a while, with occasional spikes up to 7500, the problem starts to occur near the exit when I ease off to around 3000 rpm.
The rev counter then starts to fluctuate again or drops to 0.
What’s frustrating is that it runs fine for a short while and then it doesn’t again… but it keeps stuttering until I get home. Once it’s cooled down, it runs perfectly again…
I’ve fitted a Motobatt MBTX 16U. Tomorrow I’m going to fit the one-year-old lead-acid battery.
I’ll let it cool down first and leave it in the corner for a bit…

 

[Rob]

Written before your latest update - good progress!


Okay. So you have replaced everything except the original RGS wiring. You've inspected and cleaned the earth's (including the one to the underneath of the battery tray?).

So that leaves battery (noting hooksey's comment) / charging; fusebox; ignition/kill switches and associated wiring. Given the issue is on one cylinder, that points to the section of orange/white wire under the tank that runs to the centre cylinder HT coil. Maybe check the aluminium mounting bracket is intact too.

For good measure, mebbe swop coil wiring between two cylinders (and the plug leads!) to see if the issue moves.

 

[Rob]

Battery swap would be good next step

 

[Rob]

I'd also try disconnecting the green/red revcounter wire from the coil (think there's a bullet connector somewhere under the tank). That'll remove a potential wiring fault where it runs up to the instrument panel around the steering head.