carb adjustments

[pdx_r100s]

your comment here raised a question for me:

You can do it either way. You can shut down one side at a time by screwing in the mixture screw all the way and then adjusting the opposite side. Then precisely count the turns (so you can later put it back exactly where it was) while screwing it back in to shut off that cylinder and do the other side. Only screw them in until they seat very lightly, too tight can break off the tip. You can also take them out just to confirm that one of the tips isn't broken off and stuck in the hole, something I've seen more than once.

This makes it sound like the engine would be able to run with the fuel screw on one side out (close to where it should be) and the other side fully screwed in. Is that true? When I said that the left screw shut off the engine but the right screw didn't, I started by screwing in the left (leaving the right out), and the engine died. Then I backed out the left to where it was and screwed in the right, and the engine didn't die. So now I'm wondering, does that actually mean that the right side idle circuit is clogged? Your comment above sounds like the engine *should* run with the left side screw out and the right side all the way in--I could then fine-tune the left-side mixture.

Maybe I'm misunderstanding...

[gspd]

These things are so much easier (for me) to actually do than they are to explain.

Maybe this will simplify and/or clarify the procedure...
Once the engine has reached operating temperature turn it off.
Disable one cylinder by disconnecting one spark plug cap.
Put a spare spark plug in it and rest it on the cylinder fins or cylinder head.
Start the bike in one-cylinder mode.
Never crank the engine with the HT wire not grounded or not firing a grounded spark plug.
That could blow your coil.
With it running on one cylinder, adjust the mixture and idle speed as you would a Briggs and Stratton lawn mower or any other single cylinder engine. Turn the screw in till it runs crappy, then back it out until it runs good. When the engine is in this 'single cylinder mode', turning the mixture screw all the way in must stall that cylinder. If that cylinder keeps idling, you have a blocked idle circuit on that side. (fuel is somehow getting sucked in via the main jet). Next, repeat the procedure on the other side.

Once you are confident that both your 'single-cylinder' engines idle well and can be stalled by shutting off their respective idle circuits, hook every thing back up and continue what you were doing. You're on the right track.

Does this Help?

[pdx_r100s]

That description makes sense, thanks. However, I read somewhere (perhaps the snowbum website) not to do this shorting method for a dual-plugged engine. Additionally, the instructions that came with the new electronic ignition (enduralast) said not to use this method with the ignition, so I had not been using this approach.

I was curious to know if I could achieve something similar with the method you seemed to describe above: screwing in the opposite side fuel screw all the way.

[Kurt in S.A.]

A little difficult to short both spark plug wires at the same time. IMO, it's OK to use the shorting method on an electronic ignition on a single plug system if done properly and smartly. I put the blade portion of the screwdriver on the engine and then firmly and quickly move the shank of the screwdriver to the shorting stem on the spark plug. When done shorting, keep the blade firmly grounded, and move the shank off of the shorting stem. Don't linger when moving the screwdriver.

Kurt in S.A.

[gspd]

That description makes sense, thanks. However, I read somewhere (perhaps the snowbum website) not to do this shorting method for a dual-plugged engine. Additionally, the instructions that came with the new electronic ignition (enduralast) said not to use this method with the ignition, so I had not been using this approach.

I was curious to know if I could achieve something similar with the method you seemed to describe above: screwing in the opposite side fuel screw all the way.

oops! Sorry!
You're correct on that one, I forgot you had 2 plugs per cylinder.
You'll have to disconnect the power supply to the lower coil to use my method.
Another thing I have done (but nobody else seems to agree with me on, not sure why) is to have one coil fire both right side plugs, while the other coil fires the 2 left side plugs. That way you'll know right away if one system fails. I remember doing many tests on 4 plug setups in the 70's, when dual plugging was the cool thing to do. Cutting out the lower plugs under many different conditions (with a toggle switch to the coil) made virtually no difference in how the bike felt and ran, even on a dyno. (BTW - Airheads hate dyno testing) Many 4 plug bikes have come in for service over the years with only the upper 2 plugs actually working. You'll actually be real lucky if the lower plugs even fire after a day of riding in rain or mudding around. The lower wires are very exposed and very susceptible to corrosion and damage.
IMHO dual plugging is sort like the Emperor's new clothes scenario. I did it to all my bikes in the past, because it was cool and de rigueur then, but no more. 1 plug per side works every bit as well. I run 9.5cr pistons and Accel coil. I always use the highest octane fuel available. Runs like a bear, never pings. I would never contemplate dual-plugging my present bike unless maybe if I felt the need to raise the compression to 10 or 10.5, another thing airheads really don't like (for street usage).

EDIT:
Challenge to all airhead dual-pluggers:
Hook up a switch to cut out one coil and report back if you actually detect any difference when riding with it on or off. So far, all the info I've come across (and my personal experience) over the years boasting better starting, running, gas mileage, etc. with dual plugs has been purely anecdotal. Never any real hard core scientifically proven facts. The only good side is that you have a redundant ignition system if one should fail, and get to spend some extra money on your favourite toy.

[pdx_r100s]

interesting to see this discussion about dual plugged set ups. I didn't know too much about the benefits--the bike just came that way.

You'll have to disconnect the power supply to the lower coil to use my method.

could you explain how I do that? I'm a little worried about screwing up my ignition/coils if I do something wrong.

And once I've disconnected the coil powering the lower plugs, do I simply remove one of the upper caps, put in a spare plug, and then rest it against the engine fins? Are there precautions that I need to take? This is a little different than the "shortening method" write up I read elsewhere, which seemed to describe a special tool that was used along with a screw driver. (I was having difficulty picturing how that worked, too).

One other question: if I have the engine idling normally on both cyls, is it normal for it to still run with one fuel screw all the way in? I'm trying to determine if I have something up with my idle circuit. I looked at the diagram of the bing carb and cleaned out those small air passage ways, cleaned out the idle jet, etc. And that didn't seem to change anything.

[gspd]

You'll have to disconnect the power supply to the lower coil to use my method.

could you explain how I do that? I'm a little worried about screwing up my ignition/coils if I do something wrong.

Just disconnect the positive power wire that goes to that coil. If the coil is disconnected you can't harm it.

And once I've disconnected the coil powering the lower plugs, do I simply remove one of the upper caps, put in a spare plug, and then rest it against the engine fins?

Yes, as long as the spark from the HT wire is going directly to ground, or across a relatively small spark plug gap to ground, you won't damage anything.
What you must avoid is having the coil open-fire with no ground, or any situation where the spark can jump a very large gap.
Both those scenarios could possibly damage the coil.

Are there precautions that I need to take? This is a little different than the "shortening method" write up I read elsewhere, which seemed to describe a special tool that was used along with a screw driver. (I was having difficulty picturing how that worked, too).

The worse thing that could happen is that you'll get zapped. The idea with the screwdriver deal is that the screwdriver must be solidly grounded to the head at all times, If it's grounded to the head, you cannot get zapped.

One other question: if I have the engine idling normally on both cyls, is it normal for it to still run with one fuel screw all the way in? I'm trying to determine if I have something up with my idle circuit. I looked at the diagram of the bing carb and cleaned out those small air passage ways, cleaned out the idle jet, etc. And that didn't seem to change anything.

Turning the left mixture screw all the way in must stall the left cylinder.
Turning the right mixture screw all the way in must stall the right cylinder.
The other cylinder may or may not keep on running, depending on how high its idle speed is set.
That's why I was suggesting a way you could be absolutely certain the other side is not running by disabling its spark.
If you are confused or unsure about killing the spark, another way to disable a cylinder is to empty the float bowl and then pinch shut (or disconnect and block) its gas line. This might be simpler for you, and it will totally eliminate the possibility of damaging your ignition.

[Rob Frankham]

It's worth bearing in mind that a zap from an electronic ignition can cause serious health issues.

If you're in the dry and not holding on to the metal of the bike you'll probably be OK but it's still a risk.

The issue isn't just damage by the current, a good healthy shock can cause uncontrollable spasming of muscles with consequent injury. It's not unknown for a mechanic to end up with a bike on top of them because contracting muscles have pulled an insecure machine over. Impact injuries where a spasming limb or head hits something hard are far more common. If you have a pacemaker or other electronic prosthesis, the chances of damage are far higher.

On essence, plug shorting on a bike with electronic ignition isn't a good idea.

Rob

[gspd]

On essence, plug shorting on a bike with electronic ignition isn't a good idea.

+1
Hi Rob, glad you're back, hope you're feeling better.

Experienced mechanics have figured out how to avoid getting zapped when playing with ignition systems.
I learned my lessons from experience, which is not always the best way.
I've had my share of 'zaps' over my lifetime and I'm still completely norbal.
When properly done there is absolutely no danger, but it's hard to explain the exact do's and don'ts here.
That's why I suggested that pdxr100s just lay a spare spark plug on the engine; this assures no zapping or possible component damage.

I'd be interested in hearing your opinions and personal experiences concerning dual plugging.
Also, your views on using one coil for the 2 left plugs and one coil for the 2 right plugs? (as opposed to the conventional one coil for the upper plugs and one coil for the lower plugs setups). The only advantage I see with the conventional setup is that it will allow the bike to keep running perfectly for decades if one coil fails, so much so that you'll never even know it has failed. However, the other way, at least you'll know for sure right away when one of your coils fails. (but that failure could cause you to lose the race or be late getting home)

[Kurt in S.A.]

That's why I suggested that pdxr100s just lay a spare spark plug on the engine; this assures no zapping or possible component damage.

I've done this before but you have to make extra sure that you have strapped the plug threads down so they touch the fins...and there's no possibility that they will vibrate/loosen.

Kurt in S.A.