Triumphrat

pkoteras · 05-11-2008

Hello all, glad I found this forum. I am new to Triumphs as well as working on bikes myself in general. I purchased a 71 Bonneville that has good compression, but just won't spark. The previous owner said it started fine before but he let it sit for a few months and couldn't get it started again. I can see that he replaced the spark plugs first thing, as it is obvious they have never been fired and are brand new. I've verified the plugs are the correct ones for the bike, and pulling out the plug and hanging it next to the engine casing and trying to kick start the motor results in no spark. Using a volt meter and the wiring diagram, I verified battery is producing at least 12 volts, then started checking wires for continuity. The ground to ignition is good. Checking the ground to the negative coming out of the ignition is off when the key is off, and good with the key on so the ignition switch appears good. That wire goes into an electric starter box (Micro MK-III High powered ignition unit) and out to the negative on one of the coils. I get no continuity with the key on from one side of the unit to the other. Thinking I was on to something, I pulled out the wiring diagram and rewired the ignition, bypassing the MK-III altogether but still no spark. Based on that, I assume that the MK-III probably allows power/continuity when I kick start it rather than continuously so I am unable to correctly test it (maybe someone can confirm that this is or is not true). So, I am at a loss right now. Not sure I need to look at the coils or the points as possible culprits, or if I was right the first time and the MK-III is the problem. Any recommended direction here?

OzBloke · 05-11-2008

pkoteras,
Firstly - welcome to the forum.

Secondly - send me a Personel Mail with your email address, and I'll send you a document that will help you understand the electrics a little better.

Now, to a few explanatory points.

The bike you have is a positive earth system, so please be careful not to confuse yourself with polarities.

The Micro MKIII is a Boyer Bransden ignition system - lots of good info on their site http://www.boyerbransden.com/

The Boyer has two basic sections - the black box "ignition amplifier" and the pickup unit. The pickup unit consist of two coils mounted on a circuit board, and fitted where the points used to go in the timing cover (behind the 3" round cover RHS lower engine casing). Also in there is a rotating plate fitted with two magnets to "signal" the amplifier unit to spark. The black box switches the battery -ve to the coils (coils wired in series), but only switches it on after the first pulse is received from the pickup. It turns it off after about 3 seconds of no pulses - saves coils getting burnt out and battery life. Both coils/plugs fire at the same time, so you get a spark every revolution.

You cannot take the black box out without also changing the pickup unit for the original points plate and auto-advance cam system, and adding back in the condensors.

Put the Boyer back in - if you can't remember how it went, the Boyer site has the wiring diagram - Kit 52 for your bike. Check the continuity of the pickup coils - under 700 ohms from where the two leads connect to the Boyer box - black/yellow stripe and black/white stripe.

with everything turn off, check for resistance between black lead of Boyer and earth (coils primary windings) - should be between 7 and 9 ohms for 2 x 12 v coils, or 3-4 for 2 x 6V coils.

With ign on, and plugs removed and placed on the head fins (still connected to leads of course) measure for 12V between battery +ve and the -ve of the first coil connected to the Boyer black lead, after kicking once. Beware that there can be up to 400V pulsed on this terminal, so don't get your fingers in the way.

Let us know what you find.

Pete

pkoteras · 05-12-2008

Pete -

Thanks for the response, I'll give your suggestions a try. I had a feeling that my logic wasn't correct about the MK-III. I'll let you know what I find afterward. I was wondering about the MK-III, as it was not listed in my Haynes manual, and thus the confusion when troubleshooting. Thanks for the help, I'll get to checking.

PK

pkoteras · 05-20-2008

Pete,

I apologize for the lengthy delay in response, we had some family health issues that suddenly arose so it was a while before I could get back to the bike. So the voltages appeared to be checking out fine, and I replaced the leads just in case after finding a pair relatively inexpensive on the internet. I'm glad you told you me about the black box ignition setup, I was wasting much time troubleshooting around that, for no good reason. Here is the weird thing; I was going to be away for a few days and wasn't going to be able to mess with it so I left it with someone who knows bikes and asked him to take a quick look at it while I was gone. He reported that he kicked it twice and it started right up. He drove it around and noticed the clutch slipping a bit, but otherwise was running fine. He swears he did not do anything other than clean the gas cap. I haven't had a chance to go pick it up yet, but I am a little confused as to what the problem could have been. I will report back to you when I pick it up and verify that I can get it started.

GrandPaulZ · 05-20-2008

Loose electrical connections are the bane of old Britbike owners.

pkoteras · 05-20-2008

That is looking more and more like a probability since I basically disconnected and reconnected all of the ignition wiring. Thanks for all the help, I'm going to keep perusing the site for good technical info.

Cheers,

Paul