Something Wierd here

My '73 750 has been running like a dream, with the headlight off. Turn it on, and it skips and burps and feels like it wants to stall. Li Battery is FULLY charged, and normally will last over 200 miles before it acts up. Only rode it 8 miles then shut it off for 4 hours....... Started right up, second kick. Turned headlamp on and It damned near stalled. Clicked off light and SO SMOOTH.


Boyer ignition. Really strange.

Any suggestions?

Are you using the stock ignition? By turning on the light are you changing the ignition position or flipping a switch. If the ignition, I would recommend pulling it apart and cleaning it. If a switch, I would hook a voltmeter up and see what it shows when you flip the switch. It might be pulling down the voltage, if so then some work needs to go into finding that cause. Such as a high resistance short in the headlamp bucket.

I recently cleaned up my ignition. There is a thread floating around somewhere that discusses using epoxy to mimic a Honda ignition. I didn't go there as I felt it was non-reversible and I wasn't sure I wanted to glue my ignition together. But it did profit from a good cleaning. The clicks on the ignition are provided by a spring and plunger which benefits from cleaning and I polished all the contacts with slightly radiused edges so that the whole thing works smoother. And yes, the contacts at the 6:00 o'clock position were green, apparently from something I had sprayed into the key slot to lube it settling there.

Russ

sounds like a wiring/switch issue(s), start by looking for clean tight connections

I am going to have to check the whole friggin thing. It has a Boyer ignition and I am using the headlamp switch mounted on the lamp shell, not the key. any other suggestions?

I had a gel battery which went high internal resistance, voltage checked out ok but amperage output was limited and had to disconnect the fuse and get home on the capacitor as it was dark I had to have lights.

IMO, that symptom is either a worn out ignition switch (as russ said above) or poor grounding somewhere (not excluding a corroded battery terminal which is limiting conductivity)

Because it's involves the headlight, you should open the headlight shell and make sure there aren't any skinned wires in there. Then check all the bullet connnectors for corrosion, and finally make sure all the grounds are solid. Adding extra ground wires is always a good thing. If your isolastically mounted engine has a corroded ground wire, your spark will be weak. Adding extra grounds to the engine helps prevent weak spark due to an engine block who's isolastic mounting prevents grounding through frame mounts.

Put a voltmeter across the battery terms, observe, start up, observe, switch on headlamp, observe....

Report back findings.

Or the H4 wires pushing into one of the connectors in the H/L shell. Hang it out and then try it.

steveyacht said:

My '73 750 has been running like a dream, with the headlight off. Turn it on, and it skips and burps and feels like it wants to stall. Li Battery is FULLY charged, and normally will last over 200 miles before it acts up. Only rode it 8 miles then shut it off for 4 hours....... Started right up, second kick. Turned headlamp on and It damned near stalled. Clicked off light and SO SMOOTH.


Boyer ignition. Really strange.

Any suggestions?

Click to expand...

I've hooked up an old speedometer light bulb and socket in parallel with the white power wire going into the Boyer's black box to diagnose intermittent missing that only occured when riding the bike. I leave the bulb laying on top of the headlight shell where I can see it.

If it's due to a bad ignition or kill switch you'll see the light flicker as the bike misses and you can bypass the switches to see which one is causing it.

In your case I'd check the battery voltage with the ignition on and with the lights on. You might want to check the voltage at the black box itself to make sure you don't have a voltage drop.

Just wanted to follow up on this for future reference.

First, I put the Li battery charger on the bike and fully charged it. Put a volt meter across the terminals and it was around 12.6 volts a couple hours after I disconnected the charger. While I was doing this I noticed that some of the wires on the positive terminal were "kinked". Must have happened when the terminal screw was tightened. Took it apart and found a wire that was nearly separated inside the insulation. So, repaired/replaced all wires that I suspected may have been compromised....soldering on new ring ends and using heat shrink tubing for good measure.

Next, I took off the ignition switch and found some terminals that had some corrosion. Cleaned those up and re-crimped the female ends, then putting all back together using some di-electric grease.

After all of this was done, I checked the spark plugs. They were fouled, even though they were nearly new. Since I bought this bike new, in 1973, I still have the owners' manual as well as an old Chilton shop manual. I did some reading and found that the original spec plugs were Champion N7Y's. The plugs I had been using were NGK B7ES. The B7Y cross references to the NGK BP7ES. (This is the extended tip spark plug, which places the spark closer to the center of the combustion chamber.) So, I bought a set and installed them the same afternoon.

Results were fairly amazing. Once do a key off, choke on (Single Mukuni) "prime" kick, I turn the key on, kick through with about a 1/4" throttle on and BANG! Started right up! Shut off the choke immediately, held the idle at around 1500 for a minute, then rode SMOOTHLY away. Have not had a fouling problem since.

Now, I don't know what made the biggest difference, but I am happy as a carnivore in a meat market!

Since, I have ridden up to 200 miles on same afternoon with out any problems at all. I had nearly forgotten how nice this damned thing runs! I have been putting more miles on her than my Victory Magnum!

We have since celebrated our 45th anniversary with New Castle Ale and some fish and chips!

There's a good lad.