Triumphrat

fogcutter · 07-05-2009, 08:29 PM

Need some help. I have a 70 Bonny. Stock motor new,stock carbs, new also. everything on the bike is new. Boyer Mk111 ignition with 6 volt coils. My problem is this. When I have a fully charged battery,14 volts, this thing runs fantastic. However after running for about150 miles she starts to falter and just keeps getting worse until I charge the battery again. EVERYTHING, and I mean everything checks out as OK. Went through the wiring,the charging everything. The only thing that I can come up withis the possibility that the battery is too small. I have an 11 amp battery in it. If I leave the bike sit for about a week the battery voltage drops to around 11.5 volts and the bike runs like crap. Any suggestions from you guys would be very helpful.I have checked out the wiring numerous times by myself and by an old Triumph mech. Everything fine.

KADUTZ · 07-05-2009, 10:29 PM

if what you say is true about checking out everything the alternator is alternating the rectfier is rectifing and the zener is zenering so the charging system is up to par and charging the battery which is bubbling happily along. you say you have a stock engine and carbs but something tells me the bike might stock like a'59 chebbie lowrider is stock. the OEM battery for your bike was a PUZ5A which was a 8amp hr most places will try to sell you a 12N7-4B1 (7AMP HR)as the replacement battery.
Triumph of America had a service bulletin out in 77/78 time frame that suggested replacement of a PUZ5A battery in the US with a 12N9-4B1(9AMP HR) when the original failed. 1979 Triumphs were in fact fitted with the 12N4B1 as OEM. Soooo what I'm gettin at here is an 11AMP battery is not undersized AND I dont think you can get one in the stock battery box. I use 12N9-4B1 in my more or less stock 70 WITH a piece of old inner tube under the battery strap to insulate the seat pan from the battery terminals. By the way Boyers are VERY voltage sensitive and if you have an old battery could be part of the problem. However I think your problem is you arent recharging the battery as you are riding. A stock 70 Bonnie with up to speed charging system was break even at 2700RPM with the headlight#446 bulb(50/40w)/taillight#380(6/12W) on. what bulbs do you have in the bike? H-4 is probably 55/60W I forget what an 1157 is but the draw is greater than the 380 lucas bulb. I suggest your problem is not the bike but your not riding fast enough (RPM wise) to recharge the battery (that may need replacing anyway)
ya know kinda like going to the bank once a week depositing $100 while withdrawing $200 and wondering why after a few years you went broke
jus the K's pinion.

thirdbike · 07-05-2009, 10:58 PM

You say you let the bike sit for a week and your voltage drops to 11.5 volts. If this is with the battery disconnected (or fuse pulled), then your battery is no good. If it does this only when connected to the wiring harness you have a high resistance short. Either way, it is like filling a pail with a hole in it. If you pour real fast, you can get it full but it ain't gonna stay full.

Blue09SE · 07-05-2009, 11:37 PM

Assuming that your bike still has its original alternator:

After some 28 years and 75K (?) miles, my '69 650's alternator rotor had lost so much magnetism that I had the same problems that you did-the battery would not charge with the lights on, running at my customary revs. Even at revs well over 2700, the ammeter needle just barely hit the midway mark. The Lucas rectifier, Zener diode, and all charging system wiring were all OK.

I considered having the rotor "recharged" to restore its magnetism; I understand that this can be done for Bosch (Volkswagen Beetle) 6V permanent magnet generators and Lucas magnetos. I was unable to find a source for this service, so instead I converted to a Lucas RM24 alternator (3-phase, as opposed to original 1-phase RM21) with a solid-state combined rectifier and voltage regulator (replaces the Zener diode).

The results were gratifying: the ammeter needle positively leaped to the midway mark at about 2000 revs, the lights were bright, the horn note was piercing, and the battery was fully-charged at all times. Starting was markedly improved with the now always-fully charged battery.

triumfant · 07-06-2009, 05:48 PM

Fogcutter, sounds like you need a new battery to me. I have the same problem and have already decided that I need a new one as well. my battery (12N)also needs charging every few days and the bike is difficult to start with Boyer E.I.

good site this triumfant.

OzBloke · 07-06-2009, 08:45 PM

IMHO, the following is the way to go (in order);
1. check all wiring and connections between alternator, through rectifier, to battery, including earths on battery and rectifier.
2. check your rectifier is working properly - all four diodes are conducting when forward biased. I can provide tests if you email me. If not working, replace with a <$5 30A bridge rectifier on a metal L bracket.
3. if rectifier is OK, replace alternator rotor with a new one.
4. if charging still not sufficient to carry load of bike, replace alternator stator with a high output single phase (160W) stator.