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Duraforce (E series) spark plug questions

#1

dewguy1999

dewguy1999

Over the years I've replaced the plug in my Duraforce (E series) mower with the recommended NGK BPMR4A setting the gap at 0.035 in. (0.90 mm) as specified on page 15 of the Operator's Manual. Well, while looking at the Service Manual today on pages 2 and 14 it specifies 0.030 in. (0.76 mm). Does it make a difference which is used? Would the 0.030 in. be better than the 0.035 in. that I've been using all these years?

On a related note, I also discovered today that the NGK BPMR4A plug is a resistor plug. Over the years, for one reason or another I've also used Champion CJ8Y and Autolite 2976 plugs. These Champion and Autolite plugs are not resistor plugs. The resistor version of the Champion is a RCJ8Y and from what I can tell Autolite doesn't have a resistor version. From what I've read a resistor plug is used to prevent interference and/or damage with radios, electronics, etc., in the case of the Lawn-Boy I guess that would be the CDI. I'm assuming that Lawn-Boy specifies a resistor plug for a reason and it has me wondering if some of the starting, running problems people have with Lawn-Boys may be caused by using a non-resistor plug?

Thanks in advance for all replies.


#2

J

jp1961

I use the Autolite XST 2976 platinum plug in my Duraforce 10323. Even if it's not a resistor plug, it shouldn't pose a problem unless you plan on installing a radio on it,,,LOL. The older points ignition generally use the .030 gap, while the electronic ignitions use .035. The Autolite plug is available at Meijers.

Jeff


#3

dewguy1999

dewguy1999

jp1961 said:
I use the Autolite XST 2976 platinum plug in my Duraforce 10323. Even if it's not a resistor plug, it shouldn't pose a problem unless you plan on installing a radio on it,,,LOL. The older points ignition generally use the .030 gap, while the electronic ignitions use .035. The Autolite plug is available at Meijers.

Jeff
Click to expand...

I bought a new NGK BPMR4A on Thursday from my former Lawn-Boy dealer as they're the only ones around here that sell NGK. Since I'm presently having running problems I decided to use the manufacturers specified NGK just in case it makes a difference. Hopefully when I install it next week my problems will clear up. I never thought of looking for a spark plug for my Lawn-Boy at Meijer and I'll keep that in mind for when I need one again.


#4

J

jp1961

I've been a big fan of Autolite spark plugs ever since I owned a Farmall Cub from the late 40's with magneto ignition. The tractor had a miss while idling with Champion plugs installed. A Farmall mechanic (from Capac) said to use Autolite plugs, which I replaced as a 'yeah right' attitude,,,he was right the Autolite plugs cured the problem.

Jeff


#5

dewguy1999

dewguy1999

Looking around I found these definitions on NGK's website:

Resistor

At the moment the spark jumps the Gap it causes a high frequency burst of energy, known as RFI (radio frequency interference). RFI, as its name suggests, creates static on your radio and interference with other electronic equipment, including the vehicle's on-board electronic control units (ECUs).

Resistor plugs were developed in the 1960s to suppress some of the spark energy, thus lowering RFI to an acceptable level. Most Resistor spark plugs use a monolithic Resistor, generally made of graphite and glass materials, to filter the electrical voltage as it passes through the Center Electrode.

Since Resistor type plugs actually "resist" some of the spark energy, non-Resistor type plugs actually deliver a more powerful spark. It is for this reason that most racing plugs are non-Resistor types. However, in most automotive applications, a Resistor plug is required for proper vehicle operation. Use of non-Resistor plugs in vehicles that call for a Resistor type can result in rough idling, high-rpm misfire, and abnormal combustion.

Source: Spark Plug Terms (R)

Inductive Resistor

Most automotive and power sport applications require the use of a resistor type spark plug to reduce RFI and properly communicate with electronic systems. However, CDI (capacitive discharge ignition) systems have a much lower voltage output. So while a resistor of some sort is still required, a standard resistor plug would be overkill, therefore, an inductive Resistor is used.

In an Inductive Resistor design, a coiled nickel wire is inserted into the stem and held in place by a spring. The coil acts as an electromagnet, inducing a magnetic field around the center stem, creating a natural "field" resistor. This type of resistor creates around 40ohms of physical resistance, compared to the 1000-5000ohms of resistance in typical monolithic resistor plugs.

A standard resistor plug, or non-Inductive Resistor type, should never be used in an engine that calls for an Inductive Resistor type. Use of a standard resistor plug can create an open circuit within the plug, ending its life.

Source: Spark Plug Terms(I)​


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