cylinder misfire: coils?

3 things. Fuel, spark and compression. Other than that it's mechanical or timing. Each has to be figured.

Dave
69S

Stephen Hill said:

In the case of a weak or nonexistent spark on one side, the Boyer can't be the issue. The unit fires on both sides simultaneously, and as far as the Boyer is concerned, one side is the same as the other. If you are still thinking ignition, start by swapping the plugs, then the coils and see if this swaps the problem from the left to the right cylinder. Look the wiring in and out of the left coil, looking for chafe or bad connections. Make sure the high tension lead from the coil to the spark plug has not chafed away its insulation and is grounding on the engine. Not much clearance in there and lot of opportunity for shorting, which will come and go at different revs, making you think it is carbs. If you decide it is a coil, there is probably no overwhelming reason to go to a new style of coil. If you are replacing the coil, make sure you end up with two 6 volt coils.

Stephen Hill
Victoria BC

Click to expand...

The Boyer can and will produce a misfire in one cylinder. It's disingenuous to tell others that it can't. I'm not trying to be prickly here, I just don't want others to spend endless hours troubleshooting needlessly everything but the Boyer. The wires from the pickup coils are notorious for fracturing some short distance from the solder connection to the pickup coil. This definitely will result in a misfire in one cylinder. The miss usually occurs from idle to ~3000 rpm, causing you to suspect the idle circuit in the carb. If you have a Boyer and a misfire on one cylinder, the Boyer pickup leads are the first thing I'd check. BTW, you will not see the wire fracture, its inside the insulation. I've had two Boyer fail in this manner. Both were repaired by replacing the wire. Ron L's suggestion of drilling out the solder connections and replacing with brass 4-40 screws is the definitive fix. Affix the pickup wires to the screws with CRIMPED on ring connectors. DO NOT SOLDER!

A bad engine earth can cause misfiring on one cylinder with a boyer, I fixed the exact same problem eg left side misfire with a new earth engine to Boyer earth and then another back from there to the battery using battery cable. Before finding the fix I had changed out everything but all that did was change the misfiring from the left to the right. No idea why it works but maybe a bad earth will only allow enough current for one plug to fire inside the cylinders.

Ditto on "do not solder."

I've found several cases, in automobiles and bikes, where wires broke inside the insulation, away from a solder joints, but where the tinning ended and the untinned wire began. In each instance the break was of a solder joint made by me, or by a previous owner.

I know of no original equipment automobile or motorcycle manufacturer that solders joints, they all use crimp connectors. If I do solder a joint, I insert a splint, usually a waste piece "zip tie," the clipped off end, under the shrink tube or tape insulation to support the wire after the point where the tinning ends and the flexible wire begins. Doesn't hurt to add a splint to a crimped connection either.

" the Boyer pickup leads are the first thing I'd check. BTW, you will not see the wire fracture, its inside the insulation. "

Hey Jim,
how do I check if it is the Boyer if I cannot see the wire fracture?

"I know of no original equipment automobile or motorcycle manufacturer that solders joints"

Absolutely right! Further, nor do any marine manufacturers. In fact the American Boat and Yacht Council (ABYC) electrical specs specifically state soldering is not appropriate for marine use due to vibration.

Hey Jim,
how do I check if it is the Boyer if I cannot see the wire fracture?

Click to expand...

I use a digital multimeter. Disconnect the leads inside the old points cavity. Connect one meter probe where the wire is soldered to the of the pickup coil, the other to the end of the same wire. Wiggle the heck out the wire, looking for a change in resistance. A steady zero ohms is what you want to see. If you intermittently see any resistance, the wire is faulty.

When wires are soldered, the solder travels some length up the wire from where the solder is applied. This turns the wire into a solid wire. Solid wires break when subjected to vibration. The soldered wires on the Boyer stator plate are especially vulnerable.

Only thing I have to do is to leave it there untouched for 5 mins.

Click to expand...

Wouldn't an electrical problem be more random? If it "always" restarts in the exact same amount of time, I would think more about fuel flow. Slow fill bowl, etc. Have you checked the fuel filters?