Boyer MK3 Ignition

Yorkie · Saturday at 2:34 AM

I feel kinda stupid posting this one but maybe my energy or enthusiasm for this bike is at a low. My recently rebuilt '72 is having ignition timing problems. I took off the timing cover to fix an issue (my own fault) where I had reversed the oil pump gasket. I reassembled the parts and now the bastard wont start. I have a nice spark but the bike pops and bangs out of the exhaust and will not start. I swear its an ignition timing problem and here is the process I used to install the tripper parts:

1. Set the left cylinder to TDC
2. Rotated back to 31 BTDC using the stator marks
3. Losely fit the magnet plate
4. Set the ignition coil plate to center of the adjustment slots
5. Lined the magnet screw to the hole above the left side coil.
6. Tightened the magnet plate taper screw.

What have I done wrong in this sequence? I have advanced and retarded the coil plate and it makes no difference. Battery is charged (the bike has a CNW E-start) and fuel is flowing into the carbs. I appreciate that the degree marks on the primary might be a little out but I used them in the past and it started. Thoughts?

Fast Eddie · Saturday at 3:02 AM

How did you find TDC?

If using the marks on the rotor it’s very easy to be 180 degrees out…

Also possible that you’ve disturbed the (already known weak spot) of the wiring on the Boyer back plate.

kommando · Saturday at 3:05 AM

Sequence reads correct as long as you got true TDC, I would only kick the bike for now as you really need a MK4 Boyer or any of the other EI's that do not advance at low V's. The starter will be pulling the V down and changing the timing on a MK3 boyer and risk kickbacks.

dobba99 · Saturday at 4:46 AM

As per Fast Eddie, you have the timing 180 degrees out

Carl H · Saturday at 5:01 AM

Or you have the BY and BW Stator wires reversed be sure they are hooked up properly.

vidar hjelm johansen · Saturday at 6:06 AM

I don't understand why you guys are going with the old-fashioned Boyer ignition.
Install Tri Spark and forget the whole thing.

Vidar

Carl H · Saturday at 6:26 AM

vidar hjelm johansen said:
I don't understand why you guys are going with the old-fashioned Boyer ignition.
Install Tri Spark and forget the whole thing.

Vidar

For me it is a few reasons, Cost, Ease of getting Boyers warrantied and speed of replacement parts if needed. And they have proven to be very reliable, when I install them, my way. I also carry spares in my tool kit if I or anyone needs them.

My local, USA distributor/ parts supplier, will test and confirm what part(s) are bad and replace them free of charge, they are tested quickly with no fuss, costly shipping and promptly resolved. The MK3 and MK4 also work well with stock Lucas electrical systems, so that saves a lot of aggravation and expense.

cliffa · Saturday at 11:48 AM

Yorkie said:
I feel kinda stupid posting this one but maybe my energy or enthusiasm for this bike is at a low. My recently rebuilt '72 is having ignition timing problems. I took off the timing cover to fix an issue (my own fault) where I had reversed the oil pump gasket. I reassembled the parts and now the bastard wont start. I have a nice spark but the bike pops and bangs out of the exhaust and will not start. I swear its an ignition timing problem and here is the process I used to install the tripper parts:

1. Set the left cylinder to TDC
2. Rotated back to 31 BTDC using the stator marks
3. Losely fit the magnet plate
4. Set the ignition coil plate to center of the adjustment slots
5. Lined the magnet screw to the hole above the left side coil.
6. Tightened the magnet plate taper screw.

What have I done wrong in this sequence? I have advanced and retarded the coil plate and it makes no difference. Battery is charged (the bike has a CNW E-start) and fuel is flowing into the carbs. I appreciate that the degree marks on the primary might be a little out but I used them in the past and it started. Thoughts?

Have you checked the cable tails on the stator plate? A very common issue with Boyers is that due to the engine jumping around, the strands inside the cables break, but connect intermittently, causing misfires etc. It’s easy to check them by connecting a multi meter to each and wiggle the wires whilst watching the display. Or you can just cut the cable tie and feel for limp cables where the tie was.

robertv · Saturday at 7:19 PM

Had the same issue '74 850. Was going to can the unit. Thought I should try again. See how the two timing holes are on the left side? I flipped it 180* from there and it now is perfect. Mark iv.

Boyer MK3 Ignition

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