Spark Plug

[Ihategrass]

Hi Everybody,

At the end of last season I serviced my ride on before storing it for the winter. The 12.5 flat head engine is some 20 years old and still had the original Briggs spark plug. I changed the plug for a new one. The local store sold me an "ALM 19" showing me that their interchange stated it was the direct equivalent.

At the start of this season it would not start and backfired constantly through the carb. Eventually, to sort the problem, the engine was completely torn apart and rebuilt. It still backfired through the carb.

I tried advancing / retarding the cam and the ignition and cleaned the carb until it was almost worn out. Nothing seemed to work. After weeks of messing about I reverted to the factory settings and installed the old plug. It ran like a sowing machine!

Bottom line? It seems the Magnetron ignition system must have a resistor plug to work properly (for my engine the reference is RJ19LM). The ALM 19 plug is not a resistor type despite what interchanges may say.

Don't know why the two types should make such a huge difference as both will show a very healthy spark at the plug tip but a substitution leads to a world of pain!

For ref my new replacement plug is an NGK BR2-LM and the engine starts and runs perfectly. Looking on the bright side, learnt an awful lot about this particular engine and mine is now fully reconditioned.

Hope this might help anyone with a similar problem.

Len

 

[ILENGINE]

You issue wasn't a resistor vs non-resistor plug. Your issue was the bad replacement spark plug. You were getting good fire when looking at the plug, but not firing properly under compression.

 

[Ihategrass]

Hi Ilengine,
Not so. The replacement plug fired perfectly in my old compression jig. You don't see these very often these days but they were commonly available at one time. Screw in the plug, crank up the air pressure, (150 psi), and watch the spark through the quartz window. That's with dry air, a much harder test than with a fuel air mixture.

 

[ILENGINE]

I have never used a RJ19LM in my life. Always used the J19LM back when I used Champion. Had to throw away an entire case of J19LM due to failing about 5 minutes into replacement. Currently use the B2LM in place of the J19LM series. I have never had an issue with using non-resistor plugs with the magnetron system. And you still had a faulty plug. What you don't know is if the plug had been dropped causing a crack in the porcelain. And it sounds like you had the plug in their over the winter, so there is also the case of gas soaking in the porcelain causing an internal short.

 

[Ihategrass]

Hi Ilengine,
I can only report matters as found. It is interesting that Briggs specify resistor plugs across their range of engines as does Dempsey in his book about repairing Briggs engines. If you've never used one just wonder what service you've been giving your customers.
Just out of interest I bought a new NGK B2LM plug this morning and tried it. My engine started to backfire within a minute of starting up. Back to the BR2LM and it ran perfectly again.
At the end of the day I suppose it's up to the reader to decide whether to use standard or non- standard plugs.

 

[ILENGINE]

Hi Ilengine,
I can only report matters as found. It is interesting that Briggs specify resistor plugs across their range of engines as does Dempsey in his book about repairing Briggs engines. If you've never used one just wonder what service you've been giving your customers.
Just out of interest I bought a new NGK B2LM plug this morning and tried it. My engine started to backfire within a minute of starting up. Back to the BR2LM and it ran perfectly again.
At the end of the day I suppose it's up to the reader to decide whether to use standard or non- standard plugs.

Which is interesting because Briggs used to come from the factory with the J19LM spark plug installed. Most of the plugs I sell, install are resistor type used in OHV engines. BKR5E, BPMR7A, and BPR6ES are most popular plugs. My old Champion plug book list both the RJ19LM and the J19LM for all Briggs flat head engines. The B2LM is getting in slow demand and will probably reduce my stock of that plug

 

[bertsmobile1]

Electricity flow can not be speeded up, just slowed down
Resistor plugs slow down the flow of electrons till a larger potential ( voltage to some ) accumulates at the end of the plug
If you strobe a resistor plug then a non resistor plug, the no resistor always fires earlier
The down side is plain plugs tend to leak voltage down the nose to the base when used in ignition system requiring a resistor type plug.
If you have to use a plain plug to replace a resistor plug you should gap it about 20% larger to get the timing back to where it should be.
Note this only applies to magneto ignitions will hall effect triggers.
The other problem that happens is RF interfearence which should not be a problem in mower engines unless it is an EFI engine.

People forget that 40,000V does not magically appear at the plug
It starts from 0V and rises to 40,000 V then drops back to 0 again and it does this regardless of weather the plug fires or not .

 

[StarTech]

But RFI can drive me crazy when I listening to a QRP signal. Electric fences here are just annoying.

 

[Hammermechanicman]

I believe the original plug in question is of

But RFI can drive me crazy when I listening to a QRP signal. Electric fences here are just annoying.

CW? Set BFO slightly off center of freq and set bandwidth to 1 KC. Will sound like it is under water but will eliminate most the crap. Did you ever have to deal with the Russian woodpecker?

 

[StarTech]

That why I have narrow filter filter (250 hz) installed on my ICOM 729. Even my CB band I had install fairly narrow band filter after the reciever down convertor, It so narrow I could when folks were slightly off frequency but the variable tuning took me to the one I was talking to so I could heard clearly. I think that one was just inside the human talking frequency range but heck that was 20+ yrs ago.

I sold that radio and new owner complain about having to tune in everyone.

I probably have dealt with the woodpecker but I just ignore most of the interference. If it gets too bad I just call it a day.

My problem right now is the radio is tripping the ground fault breakers and I have been too lazy to carry the radio and antenna out to the shop.