Hitchcocks Forum

Hi guys – I wonder if you can advise me?
When running my twin-plugged (EMGO dual coil) 8.5:1 1996 535cc at anything more than ~half throttle, and with the main beam (60W) on, it misfires. If I use just pilot lights (LED), it rarely misfires and if I use no lights, it doesn’t misfire at all. So I should assume there aren’t enough amps getting from battery to power coil mainbeam – right?

The battery holds charge, showing 12.5-12.7v when not-running, so no cells are down. The system is charging with voltage across battery during idle of 14.5v. The alternator wires (across green and white) record 15v at slow idle and ~30v at fast idle so charging is OK and so are the regulator and the replacement rectifier, and the ammeter shows charge as expected. Condensor checked for charge holding and it is OK - anyway I’ve replaced it twice with standard 25microfarad (500v) new ones with no effect.

BUT, with the engine not running and the main beam+taillight on (without the coil, i.e. points open) the voltage across the battery drops to 11.8v and after 15 minutes it is down to 11.5v. If I switch off the lights and leave it to rest for an hour, the battery voltage comes back up to 12.5v.
SO should I assume the battery is bad or is there something else?
Cheers, ChrisD

As the main beam needs much current it is normal when the battery voltage drops without charging.
This doesnt look like a battery problem, but rather like a bad mass connection.
When higher current flows then a bad mass connection causes a higher voltage drop even with the motor on.

The battery is showing good voltage, they should be 12.6V when new (2.1V per cell). The headlamp is 60W = 5A current needed. The alternator is supplying 14.5VDC at idle, this is good. However the alternator, even though it can supply the volts, may not be able to supply enough amps with everything on, about 100W est (+tail, brake, indicators, pilots, centre-line marker 'side lamp' and sparks). If it cannot provide enough amps then its output voltage must drop until it can push whatever current it has available through the resistance (to satisfy Ohm's Law, "ye cannae break the laws of physics").

Bauli mentions the 'mass' connection, this is what we call a ground connection, to the frame. A poor connection here will increase resistance, not good. Also check the battery terminals and the ground connection in the headlamp shell, from which there should be a ground wire running back to the frame nearer the battery (as the steering head bearings aren't very good electrical conductors), check continuity resistance from there to the frame and battery earth terminal. Also check the spade connectors on the coils as these can corrode (pull off, push on again, to scrape off oxide). Basically go round the bike and ensure all electrical connectors are good, especially the frame ground return points.



There is an off chance the bulb is faulty, they can fault so both filaments light drawing 60+55 = 115W. That can also happen if you get the three wires criss-crossed, filaments in series. Main-dip-ground instead of main-ground-dip.

That the battery volts come back up indicates it is 'quite good', I'd get worried if it dropped below 11V. However an old battery can show good volts and not be able to provide enough amps, the cells can get sediment in them which increases the internal resistance. I assume the electrolyte is topped up. Hence its volts drop to 11.5V - a 60W (2.4ohm) lamp draws 5A at 12V but only 4.8A at 11.5V. A proper 'battery tester' would show the actual condition of the battery.



So it could be bad connections or a dying battery.

It could be bad connections or a dying battery.

Not sure from the title exactly what bike you have, but if it's a 1995 indian bullet, then a glance at the wiring diagram might help...



Main lamp 40W/45W. And being an Enfield, think yourself lucky that it's got electrics and not a candle holder on the handlebars!



I had this problem with Tornado (1994) and switched to a 35W/35W and not had a problem since. Switching to a led tail lamp is helpful too.



For a colour bullet wiring diagram, go to my misc page and scroll down to "Royal Enfield UK Iron Barrel Bullet wiring diagram 1995" There is other neat stuff there too (Efi colour diagram)




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For a colour bullet wiring diagram, go to my misc page and scroll down to "Royal Enfield UK Iron Barrel Bullet wiring diagram 1995" There is other neat stuff there too (Efi colour diagram)




(bugger!)

The bike should be able to run straight off the alternator in stock form. But even so at best the old single phase 'Lucas' 3 wire RM alternator that EI used was good for a max of 70-80 watts. The four wire AC/DC versions not much better, and on a good day WILL crank out 80 watt but not much more. Depends on if you have an Electric start stator or a Kstart one??


Different windings, and with different internal configuration (Series ~ Parallel coils)


Your Rotor may want remagnetising? But first up you may want to confirm all charging circuit connections are sound?


And or, simply fit a higher output stator, something akin to the Lucas RM 21 encapsulated version; 110w+

Tim (and others).
I hadn’t realised the OEM alternator provided so few watts, only 70-80W. No wonder I was draining the battery faster than I could fill it. Yes, I will get a new one. On South African roads, with all the crazy fast drivers racing supercars on the same motorways and main roads as the people, with no licence and clapped out wrecks doing 50kph, then having a bright headlight in daylight is an absolute must.

Fortuitously I was going to have to spend money on the stator anyway as I now see that all three pigtails are cracked so that bare wires are showing (but not yet touching). The rotor seems OK - on the BritCycle website they state that ~18lb pull on each magnet in the rotor is nominal, and mine range around 8-9kg.

I have meanwhile tested all wires and found no large drains of power, no unexpected shorts or earths, all charging connections are good and clean and it starts and runs OK (without lights). So, maybe the new stator will be the answer – I’ll keep you posted.

Thanks, ChrisD

BTW: Scaleyback, I have a “regular” version of the 1996 500cc, not the UK or USA version. These were exported directly to South Africa in the 90’s. The wiring is not quite the same as the UK one but I have the correct wiring diagram, thanks.

The fact that if you rest the battery for half an hour and it come back to life is making me think the battery is well on its way out. A /good/ garage (or AA/RAC) should have a proper battery condition tester, one that can assess the condition of the cells; checking the voltage is not the only method. I'm assuming you have checked and topped up the electrolyte.



If the battery is going down it won't charge well and may draw too much current off the alternator at the expense of the lights etc.

This could well be the root of the problem - a battery should not 'come back up'.




With only an 80W alternator, you simply cannot pull the a lot of current off the system. The 'all the lights' numbers (about 100W) I gave above are for the C5, but that has a 220W alternator which can run a toaster The stock headlamp on a '95 seems to be 45/40W and that is pushing the limits of the 80W alternator..



Your battery is showing good voltage which you assume means the cells are alright but that may be a false assumption. The battery does go down and takes a while to recover. It should not be doing that.