Carb. setting tool - short circuit method

[Micha]

I was ordering a digital ignition system made by VAPE (PowerDynamo) when I suddenly realized that I could no longer use the method of pulling one spark plug cup, in order to set each side separately. I no longer have the safety gap electrodes from the back plate! So I'm afraid to damage the system when pulling one sparkplug cup off.
I am thinking of making an extension rod or something, that will be comfortably exposed to my isolated-handle screwdriver.
What are you using?
Or do you have ideas of how to make one from items that are within reach?

At the moment I have brown-red bakelite cups bought from Huggett many years ago.

[schrader7032]

You should be able to make plug extensions from your local hardware store. Find some threaded rod that is the same pitch as the removable tip on the spark plugs. That way you can cut off the section of rod and screw it into the tip...be sure it is secure, maybe use a smaller nut to jam up against the tip.

Because of the electronic ignition, you should be careful with how you short. If you do it firmly and with purpose, it should be fine. Start by taking your isolated device, like a long handle screwdriver, and place the blade against the engine. When ready move the shank of the screwdriver directly to the plug extension. Do the opposite when you're done shorting. Don't put the shank against the plug extension and then hunt around to get the blade end on the engine...that gives the spark too much of a chance to jump to ground which isn't good.

[Micha]

Thanks Kurt.

I think I will go on the safe side: before turning on the engine I will disconnect the side I'll work on and vice versa.
Each time I turn the engine off and only then I will disconnect here and connect back there ...

Thanks again for your time.

[schrader7032]

So what do you do with the unconnected side?

[Micha]

I intend to tune only one side at a time, with the other side disconnected from the sparkplug. When one piston is well calibrated in terms of its carburetor, I will shut down the engine, disconnect it and connect the opposite side and work on it.
What do you think?

[schrader7032]

The concern is that the spark energy should always have a path to ground. For instance, when you used to pull the spark plug caps on the regular magneto ignition, the energy couldn't go to the cap but instead went to the safety gap to find ground. If the energy can't find ground, then it reverberates back towards the source. This returning energy can kill the sensitive electronics of the new ignition system.

That is why one can use the shorting method as I described, because you give the energy a way to find ground. Note that a spark plug threads are ground because they touch the engine, and the electrode on the plug is also connected to the threads. The spark energy comes down the high tension lead and jumps the gap to ground. All is good.

So you can't just pull the plug cap and let it lie around. At a minimum what you can do is to take a spare plug and insert it back into the high tension lead and find a secure way to touch the spark plug threads to the engine case. I typically just use a rope or something to secure the threads in place. I've heard of people coming up with a jumper system, consisting of a set of alligator clips on each end with an insulated wire between them. One clip has to be big enough to go all the way around the threads...the other clip just needs to be able to latch onto an engine fin at a convenient spot.

[Micha]

As always, great explanation and ideas.
I really appreciate it.
Manny thanks

[dosgatos]

Years ago I replaced some broken spokes. I cut an old spokes to about six inches and the nipple screwed right on to the sparkplug. I let the sparkplug cap rest on the other end of the spoke and used an alligator clip with an attached piece of wire to short out the plug by grounding it to the barrel. Did that for a long time before I bought Mikunis for my R75/5 and installed vacuum takeoffs for a mercury monometer.

[jwonder]

I seriously hate the practice of balancing the two cylinders by pulling the plug wire. It is crude and in my opinion is not the best way to perform this task.

I have used the procedure as highlighted at Duane Ausherman's website available at https://w6rec.com/adjusting-the-2-bing-carbs/ under the "BMW motorcycle carb tuning procedures, by ear" section. It works VERY well and is quite exact.

My crib notes are below, but you really should read Duane's full writeup as its very detailed and good.

1) Start with both air screws at the suggested setting (1 turn or 1-1/2 turns out)
2) Turn the left carb idle screw in 1/4 of a turn to increase the idle slightly.
3) Turn the right carb idle screw out slowly until the motor is almost ready to die and then go back in 1/8-1/4 turn until it a consistent, but very low idle.
4) Turn the left carb air screw in and out until you find the locations where the motor runs rough and then adjust the air screw roughly 1/2 between the two points and then turn a bit more in (1/8 turn in). This richens the mixture to help get the motor to rev off idle easier.
5) Turn the right side (the other side) idle screw back up and the left one down repeating #1-#3 above but reversed.
6) Repeat step #4 above but for the right carb.
7) Bring the idle screws back to where you think they should be.
8) Get on the floor behind the motorcycle and listen to both sides. You will be able to clearly hear one side that is stronger than the other. Adjust the idle screws so both side are the same. I have found that using a piece of cardboard to block the sound of one side helps fine tune it.
9) Adjust the throttle cables so they have the SAME free play on both sides. This is important to ensure the slides are pulling at the same time!
10) Go for a ride and enjoy.

I can guarantee that Duane's method works wonders and will let you find out if you have a bad side. I have been able to debug dirt in the carb by getting on the floor behind the motorcycle and listening. It looks strange but it works.

By the way, my motorcycles tuned using this method will idle all day long on one cylinder beautifully. You almost don't know the one cylinder is not firing!

Good luck!!!

James

[Micha]

Thanks a lot.
Meanwhile, the PowerDynamo is still on its way from Salis in the NL.
I'm waiting Patiently.