New from somerset, Uk
Posted: 12 Mar 2022, 12:17
Hi All
Had my crm mk2 for about 10 years - but its been in a barn most of the time, so its only done 11k km. Bought it at salvage auction and my boys used it (very little) as a field bike.
Anyway - now have some time - so I decided to get it going again.
Made a fool of myself pretty quickly.
When I put fresh fuel in it and fired it up (remarkably with only a few kicks, after 4 years of non use) it ran OK for a minute or so then started doing something wierd - revs rising at idle, not not shutting off with key, wouldn't take any throttle.
Nothing obviously wrong with the carb so I assumed it must be the crank seals.
Took the motor out to do them (mistake!) did n't split cases as all bears felt good and mileage is low - but it did give a good opportunity to unseize and grease the swingarm pivot and lube all the shock bearings.
Afterwards no change in behavior.
So I ran it for longer and it just cleared up. Now guessing old fuel / oil deposits in the bottom of the cases were to blame. But who knows?
Anyway, got the thing MOT'd and had a good days riding in Rhiada with mates. But part way around it stopped starting on the kick start.
Luckily I could bump start it OK and took care not to stall and be careful where I stopped, so completed the day OK.
Back home discovered that the problem is a strange one.
It only won't start when the lights are on - in particular when the headlight is on. Nothing wrong with the bulb - but when it is lit the 12v drops from 13.6v *no lights) to about 6.6 to 6.9v with lights on (depending on revs) and the bike gets very erratic around idle - still fine at higher revs and absolutely no problem with the lights off.
Seems that when kicking it over there is not enough voltage to switch the CDI unit on when the lights are running, so no spark. But spun faster it can be persuaded to wake up and keep going. (For those who don't know, this bike doesn't use a separate alternator coil to run the ignition - the ecu, including the ignition, runs off the 12v system directly)
Nothing wrong with the lighting circuit wiring (does the same on dip or main and removing the headlight bulb makes the problem go away). I even went so far as to test the bulb with a bench power supply - it draws exactly what is expected from a 35W bulb.
Nothing (obviously) wrong with the alternator - it clearly does the job when the lights are off.
Connection to the regulator is in good condition and regulator connection to the harness is good.
I measured the voltage at the condenser connector behind the front light, so it is what the lighting circuit sees, and the ignition problems tell me it is what the ECU sees too, so I am pretty sure its not a main harness problem either.
So I suppose it must be either alternator lost a couple of phases, flywheel massively demagnetized or regulator output or return has unexpectedly high resistance.
The thing is though, that the alternator's rated output is 211W (apparently) but its fairly clear that with the lights on the voltage is collapsing with an additional load of only about 22W above the lights off base condition. So I don't really think it can be due a purely resistive loss as dissipating >150W at a connection would certainly heat things up.
I'll do some further tests and measure alternator phase resistances and voltages and the output voltage relative to the regulator case and see what I see. But I am guessing that there are folks out there who have seen exactly this before. And hoping to hear from them...
Cheers
Torquil
Had my crm mk2 for about 10 years - but its been in a barn most of the time, so its only done 11k km. Bought it at salvage auction and my boys used it (very little) as a field bike.
Anyway - now have some time - so I decided to get it going again.
Made a fool of myself pretty quickly.
When I put fresh fuel in it and fired it up (remarkably with only a few kicks, after 4 years of non use) it ran OK for a minute or so then started doing something wierd - revs rising at idle, not not shutting off with key, wouldn't take any throttle.
Nothing obviously wrong with the carb so I assumed it must be the crank seals.
Took the motor out to do them (mistake!) did n't split cases as all bears felt good and mileage is low - but it did give a good opportunity to unseize and grease the swingarm pivot and lube all the shock bearings.
Afterwards no change in behavior.
So I ran it for longer and it just cleared up. Now guessing old fuel / oil deposits in the bottom of the cases were to blame. But who knows?
Anyway, got the thing MOT'd and had a good days riding in Rhiada with mates. But part way around it stopped starting on the kick start.
Luckily I could bump start it OK and took care not to stall and be careful where I stopped, so completed the day OK.
Back home discovered that the problem is a strange one.
It only won't start when the lights are on - in particular when the headlight is on. Nothing wrong with the bulb - but when it is lit the 12v drops from 13.6v *no lights) to about 6.6 to 6.9v with lights on (depending on revs) and the bike gets very erratic around idle - still fine at higher revs and absolutely no problem with the lights off.
Seems that when kicking it over there is not enough voltage to switch the CDI unit on when the lights are running, so no spark. But spun faster it can be persuaded to wake up and keep going. (For those who don't know, this bike doesn't use a separate alternator coil to run the ignition - the ecu, including the ignition, runs off the 12v system directly)
Nothing wrong with the lighting circuit wiring (does the same on dip or main and removing the headlight bulb makes the problem go away). I even went so far as to test the bulb with a bench power supply - it draws exactly what is expected from a 35W bulb.
Nothing (obviously) wrong with the alternator - it clearly does the job when the lights are off.
Connection to the regulator is in good condition and regulator connection to the harness is good.
I measured the voltage at the condenser connector behind the front light, so it is what the lighting circuit sees, and the ignition problems tell me it is what the ECU sees too, so I am pretty sure its not a main harness problem either.
So I suppose it must be either alternator lost a couple of phases, flywheel massively demagnetized or regulator output or return has unexpectedly high resistance.
The thing is though, that the alternator's rated output is 211W (apparently) but its fairly clear that with the lights on the voltage is collapsing with an additional load of only about 22W above the lights off base condition. So I don't really think it can be due a purely resistive loss as dissipating >150W at a connection would certainly heat things up.
I'll do some further tests and measure alternator phase resistances and voltages and the output voltage relative to the regulator case and see what I see. But I am guessing that there are folks out there who have seen exactly this before. And hoping to hear from them...
Cheers
Torquil