1970 Triumph Bonneville Boyer Ignition Troubles


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1970 Triumph Bonneville Boyer Ignition Troubles 

Q: I seem to be having the same issues on my 1970 Triumph Bonneville as David Ragland has on his 1966 model (Triumph T120 Ignition Trouble, March/April 2012). My coils are both new, as are the leads. I use N3 Champion spark plugs set to the correct spark gap. The problem is intermittent, depending upon how much low rpm riding I do. Just a couple miles at 30-35mph in high gear will bring on the problem. Then it might clear out once I am back to highway speed. What and where are the trigger coils and trigger wires? By the way, my Boyer ignition is new, as well. Thank you for sharing your expertise with us mortals. Had I not seen this reply to David Ragland I never would have considered that as a source of my problem. - Jeff Young/Tupelo, Miss. 

A: Back in March, David Ragland wrote in with a problem with his Bonneville fouling one plug. I suggested several causes and a few solutions and hoped he could figure it out. He called me the other day to update me on the issues. First, he found the Boyer ignition was grounded through the battery carrier, which is rubber-mounted so not a good ground. Once he got that squared away it started firing more reliably, but still fouled the left plug. He finally pulled the head and that’s when he found the real problem. A poorly done valve job had resulted in a split intake valve guide and badly ground valve seat. That cylinder was sucking oil down the valve guide and fouling the plug. He’s now in the process of having the valve job done correctly and is confident that will take care of the fouling.

Back to your problem. The trigger coils are mounted where the points used to be, under the round cover on the right side timing cover. Vibration can fracture the wires where they leave the printed circuit board, causing intermittent ignition.

6/15/2019 3:24:31 AM

Could also be poor charging at low revs, coupled with a weak battery. The boyers go to full advance under ten volts and stop working completely under 8v. Small things like gapping the stator correctly against the rotor helps, probably time for a new rotor with fresh magnets as well. If its from 1970 its not going to be as efficient as a new one.

12/14/2017 8:16:48 AM

Power Arc also makes an ignition system for British twins as well as other motorcycle brands .

10/6/2013 11:55:05 AM

huw, I have had simular problems in the past with several bikes I was working on. Sometimes the vented gas tank cap is plugged and sets up a vacume stopping fuel flow. Other times rust and other junk can collect around the petcock screen shutting down fuel. In either case letting the bike set a few minutes will let just enough fuel by to travel a few more miles. Then again it could be electical but some misfiring would seem likely before it shuts off.

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