As an attempt to sort out 'good' from 'bad' spare electrical components, I've finally got round to fitting my 99p ebay bargain ecu and it works

But the rev counter needle now flickers above 4000rpm. The revs aren't changing , just the needle goes barmy.

Everything else seems to be OK

I'm going to put the original back as its fine and keep this as a spare but is this a sign of an impending bigger failure or is likely to be just a dodgy diode somewhere ?

Does anybody have any experince of this ?

I'd be inclined to check for corrosion on all the electrical connectors on the ECU and its associated wiring. As the revs increase so does the frequency of the pulses sent to the rev counter, which means that each one has to be of a shorter duration. At high revs this could be too short for the impedance in the connectors to permit sufficient current to flow. Similarly even slight damage to any of the wires could cause some arcing to complete the circuit which would introduce a lot of RF noise.

Words of wisdom indeed.

Having put the original ecu back in, the rev counter is still flickering

Guess I've got the choice between leaving it alone or fiddling and possibly doing more damage to the connectors or the wiring.......

Started misfiring under load above 4000rpm in sympathy with the rev counter

Guess I be fiddling with the connector a bit more shortly.....

Luckily I now have another one to drive

It's getting worse.....

There is now a big misfire accompanying the flickering and it's happening from c.3000rpm under anything but a light throttle.

It it gets much worse it won't be driveable

I changed the coil today with no effect and having a hard look at the connectors made no difference either

Ignoring the fact that this happened after I'd 'moved' the engine ECU harness, would there be any alternative explanations for these symptoms ?

Have you checked the ignition unit that is bolted to the bulkhead just below the washer bottle, it's the grey box with cooling vanes on top.
They can some times give those symptoms, try swapping with the one from the cab.

Thanks - that's one part I haven't looked at yet.

Good idea about swapping the bits car-to-car too.

If it is that, the 216 SOHC at the local scrappy is likley to still have it's one , if I'm quick.....

so, a bummer of a weekend, then .....

as you say, lucky you have another

i'd be tempted to try the bulkhead mounted unit [ignition amplifier?] too, before getting too down -

however, it is a common 'error code' type display on japanese bikes certainly, that they make the revcounter dance at particular trigger points to give you a 'code' for a recognised fault ..... would well be worth asking one of the bods at work [if they're not ALL at Arjeplog !!]

the other possibility, i'm afraid, is that disturbing the wiring loom has cracked a wire that has age hardened its casing .... there'a a needle in an haystack somewhere thats easier to find .... but i know a man who can, if it is left with him .......provided it drives down this way

keep me updated & bon chance

T

Nope, swapping the finned ignition unit hasn't had any noticable effect.

It's still just about driveable

Still trying not to think 'wiring harness'......

When you say you moved the ecu wiring harness what exactly did you do? As this fault appeared after you Moved it then i would be checking there, maybe there is a bad connection or something.
But i would say it's electrical related and not fuel.