TR2/3/3A TR3A Misfire

[mapleaf]

Checking out a misfire in my TR3 I pulled the plug wire from the #4 plug and held it back about 1/8" from the plug. The spark jumped from the wire to the plug and the misfire went away but when I reconnected it the miss returned. Any ideas? TIA

 

[Geo Hahn]

Just a wild guess -- could your misfire be in another cylinder and when you pulled #4 (taking the spark away from the cylinder) you were then running on 2 cylinders instead of three?

At idle I think these engines can run remarkably smooth on just 2 cylinders.

 

[Dale]

Or, could you have created a "booster gap" when you held the plug wire off an 1/8" and caused a fouled plug to begin firing? Pretty off the wall I admit, but.

 

[TR3driver]

That's a classic one ... like Dale said, your plug is fouled or glazed. A new plug should fix it.

What happens is that the insulator gets a slightly conductive coating on it (the fouling or glaze) which bleeds off the energy from the coil before the voltage rises high enough to jump the gap and causes it to misfire. By holding the wire away from the plug like that, the voltage high enough so that when it does jump from wire to plug, it jumps the plug gap before the glaze has time to bleed it off.

If it's just oil or carbon fouling, sometimes you can even clean the plug up enough to work. But if it's glazed you'll have to either clean off the glaze or replace the plug.

 

[sp53]

Buy a set of Champion plugs. If you go to your favorite store and ask for 67 tr4 plugs, you will often get better results than asking for 50 something tr3 plugs. Most store computers still list the later tr4.
steve

 

[mapleaf]

Thanks guys, You're right, the plug is badly fouled and I thought that may be causing the misfire but I couldn't figure out how it would fire with the wire disconnected. Thanks for the explanation. Randall. Anyway, the plugs are Champions and only have about 300 miles them so I'll clean up the fouled one see what happens.
Oh, one more question: fouled #4 plug after only 300 miles, rear carb too rich??

 

[Deleted member 8987]

sooty or wet?
If wet, is it oil or gas?

 

[mapleaf]

I cleaned the plug and now it's running smoothly.
The plug was covered in black soot. Carb setting too rich??
TIA

 

[TR3driver]

Well, too rich for some reason. Could be carb setting, but could also be something else like a stuck choke, leaky float valve, worn jet, valve adjustment, etc.