Ignition Coil and Idle Speed

[sign216]

What is the amperage of the trickle charger?
It might be too low to make a difference.

Crutschow,
I mispoke. It's not a trickle charger, but a "smart" charger that adjusts the current to the battery's needs. It's a lower level brand , Mabars, and doesn't have any output data. The output is way beyond the tiny amp capacity my multimeter can measure.

Is there a way I could rig something to measure the amps?

The bike's generator is so weak, and battery so small, the charger must have significant influence. Could I be wrong? In normal use it charges the battery fairly quickly.

 

[shortbus=]

At 2,000 rpm the battery is 6.15 - 6.45 volt.
At 1,250 - 1,350 rpm the battery is at 5.72 volt (tail light is on).
It would not reliably idle below 1,250, and connecting a trickle charger to the battery did not smooth out the idle or let me turn it lower.
At lower idle speeds it ran rough and stopped.

This makes me think both your battery and your generator/alternator are bad. I has nothing to do with the ignition points or otherwise. A generator will pull down the engine, trying to charge the battery. But in this type small engine the ignition is just along for the ride, no changes with RPM or load, the contact plates are screwed directly to the engine cases, no vacuum or centrifugal advance in them.

 

[Ylli]

Does that carb allow you to adjust the idle mixture? It might just be running a bit too lean.

 

[shortbus=]

Does that carb allow you to adjust the idle mixture? It might just be running a bit too lean.

If it uses the type of carb I think it does, yes it has idle screws. But they, Amal/MiKuni or any of the slide type will not let the idle get low enough if there is a vacuum leak between the carb and engine. The back side of the round slide has a scallop cut in it, and this leaves the main jet open to the air flow into the engine. A vacuum leak will allow this air to pull fuel into it, keeping the idle higher than it should be no matter what the slide setting.

 

[Diver300]

A more powerful spark may help to ignite the fuel if the mixture isn't quite correct. Transistor ignition may help that.

Capacitor discharge ignition was one way of getting a good spark at all speeds. I think that more modern ignition systems have very low resistance coils, where the current is limited by delaying the turn-on time of the transistor, depending on the revs. That is much simpler than a capacitor discharge system, but needs more processing power.

 

[sign216]

Ylli, If anything it's running rich, as the plug is black, although that could be from all the idling, trying to get the bike running well. There is an air/fuel mixture screw, and I've adjusted it w the idle speed screw to get idle lower. Although I could do more w the mix screw, now that I've got the transistor ignition. That will be next, but I expect the changes to be minor. Note I replaced the orig. simple carburetor with a more sophisticated new old stock Dellorto. It's in great condition (new) and a big improvement over the orig. equipment.

Diver, in another thread last year, I explored getting a high performance coil for this bike. The consensus between this board and the coil manufacturer is that it wouldn't work. I'm trying to remember.....and I think it's that w a single cylinder engine the dwell is very long and would overheat the coil. The performance coils are made for multi-cylinder 12v engines, and not suitable for vintage single cyl. 6v bikes. I bought a performance coil, and tested it out on the bench, re dwell and overheating. I recall the tests were good on the overheating, but there wasn't any spark improvement over the 50 yr old orig coil, so I'm running that.

Shortbus, the generator is known on these bikes to be too weak, barely charging the battery, so you're right there. But the battery is less than a year old, although it's only 6 or 8 amp-hr, which is small by any standard. I could modify the frame to fit a larger battery, or go lithium, but remember; hooking up the charger while running didn't affect the idle performance. If the added input of the charger didn't affect things, I feel a larger battery might be a wasted effort.
Am I wrong on this?

Joe

 

[crutschow]

I feel a larger battery might be a wasted effort.
Am I wrong on this?

No, that sounds correct.

 

[sign216]

No, that sounds correct.

I'm happy to get a larger battery, but remember with the charger hooked up, nothing changed. So isn't this a wasted effort?


P.S. It looks like I can get a 20 to 30 amp hr battery to fit, which is a big improvement over the standard 6 or 8 amp hr battery. I agree, this has got to be an upgrade, even if nothing else changes. Although I'm fearing there might be some "slop" in the manufacturers estimate of battery amp hours. What's the board's opinion?

 

[Ylli]

Deleted

 

[alec_t]

IMO a larger battery would make no improvement to the ignition: it would merely give you a greater reserve to power the lights etc for longer with the engine off.

 

[sign216]

Thank you all for the help.
My electrical knowledge is "basic" and it's great to be able to ask a knowledgeable group about these issues.

 

[ClydeCrashKop]

If you have a vacuum leak, spraying carburetor cleaner around the intake manifold will have a noticeable change in RPM.

You might glean some accurate ignition info here: Scope Diagnosis

Maybe not relevant but more diagnostics here: Spark plug and Vacuum gauge diagnosis

 

[hyedenny]

It's not a matter of "stressing" the ignition system, it's a combination of the idle mixture not being ideal, the burn rate vs piston speed, and the fact that it's a single cylinder which is inherently not smooth at any speed. An electronic ignition has a longer spark duration, and a more powerful spark which compensates for the above, and ensures a more even and complete burn. You might try adjusting your idle mixture screw and/or pilot jet. It also depends on the size of the carb. At idle there might not be enough vacuum to pull an homogenous mixture through the idle circuit.