Topic: 400/4 DEAD LEFT HAND COILS

[MCL BIKER]

Hi! Joined the forum as I have a problem with my bike & trying to get straight forward information from any manual or part supplier is a joke.
My Problem:
1976 400/4 I have now got through 3 left hand coils, each one fails about 500 miles, I then have the dubious pleasure of trying to get bike back home.
The coils are supplied by Dave Silvers [uk] and whilst non Honda should be good, the ignition is a Mk111 Boyer. The bike has run fine for years & has suddenly started eating coils; always the left hand one. Boyer are of no use they can't even answer a straight forward question. I am thinking something relative to the left hand coil is causing the failure, what i don't want to do is buy yet another coil to have it fail whilst out on the road. The only anomaly I found tonight is that my horn is earthed on the coil connection, but cant see any reason why this should cause the failure. I believe the Boyer sends the same signal to both coils, one presumes the regulator supplies the same power into the system so why repeated left hand coil failures? Just writing this could a bad earth on the left hand coil be a problem? if so how do I check rather than just clean up, new coil fitted and hope for best.

[scottly]

This does seem a bit odd? How exactly are the coils failing?

[Kevin]

Very odd problem......I don't have the answer, but I do have a few questions and suggestions for you.

1) Has the frame been painted or powder coated?
Even if it has not been painted or powder coated, scuff up the metal a little where the coil brackets touch the frame.

2) The horn wiring does not sound right, I'd definitely check into that.

3) Are you using the same set of plug wires and caps every time you swap out coils? Could be a resistance issue.

4) How does your fuse box look? Take a look at the underside to see if it is heating up.

5) I run a relay and bigger gauge wires from my coils to my battery. Might be a good option for you too.

6) Have you replaced the spark plugs?

[MCL BIKER]

The bike goes onto 2 cylinders and when i eventually get home coil checks out at <1.5 ohms, should be around 4 ohms

[MCL BIKER]

Frame painted 10yrs ago, will check frame earth on coils but I have also been told despite my original post that coils don't need an earth.
New coils come with HT.
Fuse box and wiring loom all new Honda several thousand miles ago.
Plugs have been in for some miles, it is the coils that clearly are failing.

[Kevin]

I realize that the coil is going bad.....but the spark plug is also part of the circuit. They're cheap, replace them too.

What replacement coils have you been using? You said they come with the leads already installed which makes me think they are OEM. Are they used and 40 years old or NOS?

Do you have another ignition or points set up you can install? 

[scottly]

It is correct that the coils are not grounded. You may want to test for continuity to the coil laminations from both the primary and secondary leads, as well as between the primary and seconadry: there should be none. The MK3 is supposed to work with stock type coils, but some versions were made to use special coils, and would damage the stock type. I would verify that you do indeed have a MK3. Is the right hand coil a stock unit? The stock coils have the TEC logo, and are marked FL 703-12V.
   

[MCL BIKER]

They are brand new coils from Dave Silvers who specialize in new stuff for Honda's both here and the US.

[MCL BIKER]

They are both stock? pattern coils as supplied by Dave Silvers, not original TEC Honda ones. What's bugging me is why left hand side every time. The Boyer is definitely a MK111; says so on the unit. Everything was fine for 10K miles. I don't want to spend another 40 quid on another coil to then get stranded on side of road because I've not understood the problem. I am getting to the point of buying 2 more coils and replacing the Boyer with back plate and point buts thats another 100 quid gone!
What I really need is convincing it's not the Boyer, but I don't know how to do this they are not very helpful at all so no point having any more conversations with them?
If I was convinced it was the Boyer I don't have a problem buying another Boyer set up at 120 quid, if a new unit lasts as long as previous I will be dead and gone.

[scottly]

Found this interesting bit of info on the Boyer "pattern" Honda coils (note the warning about mounting the coils with a heat sink):

[Kevin]

Nice find Scottly, we need a "Like" button on this forum ;-)

[scottly]

Thanks Kev.

[MCL BIKER]

Interesting, Boyer never mentioned anything like this; said they were useless. Thanks for that will investigate and ponder accordingly.