Antique

My Feedback: (4)

Too much emphasis on spark plug gaps...An NGK CM6 plugged into a RC EXL or C&H ignition will run an engine with the side electrode cut completley off...
.035-.045 works well...On ANY size spark plug except the 1/4-32 Rimfire...
So much for changing the gap .002 at a time and having the engine run better, unless it was too close in the first place...
Same goes for carb needles, start at 2 turns out and tune from there, factory settings are an urban myth...

jerdavis

My Feedback: (3)

Here is a question, the answer which I have been unable to find,and I'll bet you are the guy to answer it.

I have a 26cc european built engine equipped with a tuned pipe. After a series of ignition and carburetor problems, it now has RC EXL ignition firing an RDJ6J plug.

With the plug gap at the recommended .025, it will usually start for the first flight of the day, but after that it will fire but not start unless the plug gap is set to around .018.
It doesn't seem to make any difference if the ignition voltage is 4v, 5v.

I'm thinking it could be the plug is oil fouling (since the plane is way over powered and most of a flight is at 1/4 throttle), or the ignition unit is just plain weak.
Oil is Stihl 40:1.

What do you think? Have you ever experienced oil fouling in a 2 cycle?

Jerry

Tired Old Man

My Feedback: (1)

Likely nothing wrong with the ignition system itself. Have you checked the battery condition? A 4.8v nicad of 800 to 1,000 ma capacity is plenty good enough to handle the ignition all day. better in performance than most nimh batteries.

I'm not familiar with the plug you're using, but if .018 works all the time why not gap it and leave it there? Plug fouling is easy to discern. Pull the plug and look at it. A wide gap requires more energy to bridge. This is an area I disagree with RC Ign. Although an ignition will function with wider gaps, they generally will not do so efficiently. The spark coils are forced to work harder and the energy requirements are much higher. The delivered spark will have a higher energy level but the capacitor may not have enough time to fully charge during the charge/discharge cycle. Higher rpm running makes the situation worse.

karolh

T.O.M in your experience when using the RC exl ignition what plug gap have you found to give the best all around performance. Just for the record I use a .022" gap, but then what do I know

Karol

Jezmo

I run my European manufactured 26 with a wider gap than .018" and it starts great when hot. In fact the gap is even wider than .022". After the original ignition failed I switched to a CH SynchroSpark and never have had another problem. I had to switch heads when I went to the CH and CM-6 plug as the original head took a special plug. (It was a "Brisk" plug)

pe reivers

I run this " european engine"  with several ignitions, ranging from RCexcl to Vlach, to ICU, all set at 0.020 to 0.022" gap using CM6, Brisk UR17, and  NGK BMR6F plugs.
Hard starting never is a result of the use of these parts/settings, but always is in the fuel and/or carb settings, fouled plugs etcetera.
If the carb is set right, and the plug is brownish or light tan, starting is OK regardless of slightly wider plug gaps, even up to 0.027"
Like TOM said, if the engine is operated at 10,000 rpm or more, wider gaps may not get up to the required spark energy to bridge the gap, but below that rpm, I have not seen any problems at all.

Tired Old Man

My Feedback: (1)

CM-6 plugs are factory checked at .018". I've never seen a real reason to change them. Gapping to .017" saves re-gapping every year or so. That's correct, I said every year or so. Most people will easily get two or three years out of a plug if they tuned the engine close to right. Champion plugs seem to like .022" to .025". NGK Iridium plugs are gapped according to the amount of energy the ignition can deliver through the plug. Weak/average ignitions at .018" and hot ignitions can use .025" to .032.

Easy way to check what your ignition can handle is to experiment with wider and wider gaps. When the engine starts crapping out or loses performance, reduce the gap.

Jezmo

I know this is a little off topic but my 26 seems to run best between .022 and .024. (by runs best, I mean transitions and runs smoother. I do NOT get more rpm's out of either engine with the gap set wider) It starts the same at .018 as it does at .024 but my DL50 definitely runs better gapped between .022 and .024 with the side electrode cut off some and shaped to a slight point. The plug mod has been documented in other threads here on RCU. I haven't tried the plug mod on the 26 yet.

karolh

T.O.M.

I your estimation do you consider the standard RC exl ignition as being in the hot, average or weak range of ignitions ?

Karol

pe reivers

My Experience:
 FWIW; when testing the advance curves of Vlach and  RCexcl ignitions I had to remove a small section of the braided shielding of the HT cable in order for my clamp signal pickup to work.
At the same time I was testing, I was also charging batteries (Schulze charger).
When testing the Vlach, I heard an intermittent clicking noise during ignition test runs. It turned out to be my charcher switching on and off due to high power radio frequency radiation.
When testing the RCexcl ignition, no such thing happened, indicating less radiated HF didturbance from the high tension lead.

Both ignition types need a resistor. Vlach has it in the plug, RCexcl has the resistor in the plug cap.

conclusions?
I'm not that quick on the draw.

Tony Hallo

Frpm NGK Web site;
"Since the gap size has a direct affect on the spark plug's tip temperature
and on the voltage necessary to ionize (light) the air/fuel mixture, careful attention is required. While it is a popular misconception that plugs are pre-gapped from the factory, the fact remains that the gap must be adjusted for the vehicle that the spark plug is intended for. Those with modified engines must remember that a modified engine with higher compression or forced induction will typically require a smaller gap settings (to ensure ignitability
in these denser air/fuel mixtures). As a rule, the more power you are making, the smaller the gap you will need.

A spark plug's voltage requirement is directly proportionate to the gap size. The larger the gap, the more voltage is needed to bridge the gap. Most experienced tuners know that opening gaps up to present a larger spark to the air/fuel mixture maximizes burn efficiency. It is for this reason that most racers add high power ignition systems. The added power allows them to open the gap yet still provide a strong spark.

With this mind, many think the larger the gap the better. In fact, some aftermarket ignition systems boast that their systems can tolerate gaps that are extreme. Be wary of such claims. In most cases, the largest gap you can run may still be smaller than you think."

karolh

Trying to find the correct plug gap other than by trial to find what works best for you is like trying to scratch your elbow with the same hand. I recently did a search on a spark plug cross reference site for plug gaps, and for a group of similar but different brand plugs, each brand suggested a different gap size.

Champion Y-82, gap size 0.020"
Denso U-20M-U, gap size 0.027"
NGK CM-6, gap size 0.016"

Karol

Tired Old Man

My Feedback: (1)

Which brought you right back to having to experiment....

The RC Exl systems fall pretty much into a high average voltage range. They do a real good job for our applications but there's no reaso to make them work harder than they have to. Using the correct input voltage and a reasonable gap keeps them happy for a long time. As noted in the NGK post, wide gaps require more energy to bridge, and unless the ignition has the ability to deliver large energy amounts on a high frequency basis you won't maximize the performance of the system. The coils have to receive the energy needed to bridge the gap, and the more energy required the harder it becomes for the coil to be recharged in the amout of time allotted. After a point the coil is delivering less energy with most all ignitions but the user can easily make the situation worse with excessive gaps. Better plugs can do a better job but they require even more energy... Better ignitions cost a heck of a lot more as well so people have to balance all the related factors.

What we have for what we do isn't broke so there's no need to fix it.

pe reivers

I have used the RCexcl ignitions gapped at 0.6mm using NGK BMR6F plugs, then tested them for reliable operation in an MVVS 26cc up to 9000 rpm and down to 3.5V battery voltage. I stopped at 3.5V to protect the battery with ignition still operating like a charm.
What more can I say.