I've just checked my plug gap, haven't done so in a long time,
its about 1mm, pretty sure this is too big.

What is the recommended gap for the NGK BPMR6F in a ZDZ80 ?
What are the bad effects of a misgapped plug ?

You should check your Maintenance Manual for the gap for your engine.
Most RC gasoline sparkplugs have a .53mm to .64mm(.021" to .025") gap.
If a gap is too small, there will not be enough space for the proper amount of fuel/air
to be ignited. If too much gap, the spark may not be able to jump across to ignite the fuel/air mixture.

If your ignition is weak, you can close the plug gap down a little to get it to start easier. I have run 'em with as little as .018" gap.

How do these engines behave when the gap too narrow?
What about when it's too wide?
Does it start missing or something?
(Just wondering what symptoms to look for, assuming everything else being OK)

When the gap is too wide, but wide enough to run (start), it will not rev over about 3000-4000 RPM. It will seem like a carb/fuel problem. What is happening is that the demand on the ignition goes up with RPM. It makes the gap (sparks) at idle but poops out as the demand goes up on the ignition with RPM.

With the gap too small you will be SLIGHTLY down on power. A smaller gap makes a smaller (weaker) spark. This will also affect timing (very slightly) and is somewhat dependent on fuel used and compression ratio. It's complex... But, if I reduced your gap from .015 to .013 without you looking you would not notice it by flying the airplane.

Now, if either are taken to the extreme things change. Too wide a gap, won't start. Too small a gap won't start or will barely start.

Just my .018 cents worth.

Should one check the gap on a spark plug annually? And preferably clean it also?

Gunny

I guess I am bad. I never gap my plugs!

Just read this in one of the BME manuals. This answers my question.

The gap on this plug is suppose to be 0.021 - 0.025 inches

If you are an old hot rodder / off road biker , you have been thru this exercize.
Not all plugs are created equal -not even same brands - When I ran Hodakas - the first thing to go was always the plug - simply ruined from heat and contaminants.
You could pull it - clean it, look till you turned blue and see nothing wrong --but it ran ****ty.
change the plug - presto -- back to full power .
If you are just tinkering and it all runs starts etc., nicely --leave it alone .
If you are on a quest for max power - try different plugs/gaps etc..
for all around use - I set all my ZDZ's at .025 -on Brisk or NGK.
I make damn sure I don't overheat or over prop (overheat ) and use (now ) 32-1 syn right from the get go - so far the best looking pistons as far as being clean on tops / sides - no burned look in header or mufflers .
The plugs also look new except for being darker on the porcelain

Plug gap? Humm, I use a #11 exacto blade. Always have, always will. I guess like the old matchbook for points, it works, just not complicated enough for some.

Really?
I could and did simply eyeball my points and could hit almost exactly .017 - this was a while back --on flathead Fords --
matchbooks are about .015--.018--
Xacto #11's--.020
Hard to relate these ideas to those who have never set points - or adjusted mechanical brakes --
But I got used to HEI ignition/ pointless ignition /ignition modules ,etc..
What really amazes me is my little Japanese cars which will run 200,000 miles without burning oil.
And still go like crazy.
When I was a kid - the engines needed the valves touched up by 50,000 miles and it was a rare engine which was still sharp at 100,000.
Anyway - the lowly spark plug is still the same ol piece of sh-t it always was and it is hard to forget the symptoms.

Or a worn out dime[8D] Anyone thinks they can tell the difference between .019 and .017 is kidding himself.....It's hard enough to measure .002, much less set a gap that close....The Mickey Mouse gap gauges sold nowadays probably aren't that close anyway...Dream on

I cheated - I watched the breaker cam--
You know - that bumpy thingy. Remember them?

Showing your age [8D]
Did the SDC 80 work OK ?

Dick H. are you using the mobil sythetic oil at 32.1 if so what is the name of the Mobil oil ?? Sounds like good oil at 32/1 . Thanks Dick for all your insight you to Ralph.

HODAKA !!!! Dick, you OLD dog, I have not heard that word in ages, I was one of the original Hodaka Dealers and sponcered racers back in the---- well we won't print the years. Great little motorcycle.

sorry,

Now back to our regularly scheduled program.

Ralph- SDC80 is fine - I am trying it on 100 and 80 engine -
Power is up from the slightly smaller carb I was using.
Thanks again.
The first model engine I owned was a clapped out rear intake O&R 23- which I flew in a Brave.
I learned ignitions the hard way - on greasy grimy double cap Ford V8 setups which were constantly covered with oil flung from leaky front mains and water from worn out water pumps.
The wiring was cloth covered tar and spark plug wires ran thu steel tubes - which added to the problems.
These little model engines are much nicer to work with compared to that stuff
Like other old farts - I have been exposed to an assortment of thing that go whirrr.

WHat do you guys use to test the pop-off pressure of the carbs metering pins?
That is the typical pressure of a 100CC engine?

Walbro sells a pressure gauge...10 -15 or more is typical, not very critical...[8D]
Another controversy begins