Spark plugs
 

So, Whats the deal on spark plugs? I have a Midwest T-6 that I just put a G-38 in, an old one with a magnito. I decided it needed a new plug and went to the local saw shop and showed them the old one. He got out his conversion book and said "thats a resistor plug and here is the equivalent".

When I ran it, the ailerons twitched and the more throttle I gave it, the harder over they went. I put the old plug back in and the problem went away.

I guess all resistor plugs are not the same... Do they make aircraft plugs?

bigbird<br type="_moz" />

RE: Spark plugs
 

He probably didn't sell you a resistor plug. Did it have an R in the part number?

RE: Spark plugs
 

I would concur, I don't think you got a "Resistor" plug. He sold you a replacement plug as a substitute. Since he is a small engine repair shop, radio interference isn't something they deal with or worry about. I doubt the lawn tractors have AM/FM stereo or CD players in them yet.

RE: Spark plugs
 

Most all chainsaws, weed whackers, and blowers made in the last 14 years come from the factory with resister plugs

The #1 spark plug in all these is the NGK BPMR7A

RE: Spark plugs
 

Notice the "R" in the number!

RE: Spark plugs
 

I'll check but he did specifically mention that it was a resistor plug, btw it was a bosch plug.

Thanks
bigbird

RE: Spark plugs
 

Did you check the plug gap?  It might be set for too large of a gap.
A larger gap results in a higher voltage to bridge the gap and also higher voltages result in more radio interference RFI.

RE: Spark plugs
 

Check to make sure the plug boot is on all the way. But has this engine been run on this plane without any interference problems before? Maybe something other than the plug?

Richard/Club Saito #635

RE: Spark plugs
 

I suspect you got a bad plug. Take it back and get another one. Or why not just use the old one?

RE: Spark plugs
 

No, the motor installation is a new one, however when I put the old plug back in the problem went away.

The first thing I checked was the boot, it was on all the way.

I did not check the gap, I'll check that too.

Thanks

bigbird<br type="_moz" />

RE: Spark plugs
 

The plug I got does NOT have an R in it so you are most likely right. I didn't get a resistor plug.

Thanks everyone.

bigbird

RE: Spark plugs
 

One of my kids swapped out a plug on my Homelite 30 and put a non resister plug from their weed whacker in it.

It was hit city with the radio the next time I flew it until I changed the plug back to a "R" one.

RE: Spark plugs
 

The way mine ( a classic Midwest AT-6 ) was acting, it wouldn't have survived the take off. Sounds like you were lucky to get it back!

bigbird

RE: Spark plugs
 

I just got "hits" in a certain spot in the air.

RE: Spark plugs
 

The Vlach units later than 2002 needed the R-type plugs. The ignition relied on spark feedback to run and time properly. Non-resistor plugs would cause erratic running, apart from the radio interference.

RE: Spark plugs
 

Just what do you mean by spark feed back?

RE: Spark plugs
 

just that. The ignition reads the feed back from the HT wire and uses it. This is known as "forward coupling" in regulating cirquits.

RE: Spark plugs
 

I would surely like to know how that works. There are no direct connection from the spark plug lead to the ignition circuit in the standard ignition circuit. Only thru the coil. There are no feedback connections.

RE: Spark plugs
 

Mr Vlach knows how it works, I don't. I just know for sure that the ignition runs erratic when a non-resistor plug is used.