Antique Briggs Engine Spark Plug Selection

[JHZR2]

I’ve asked about the old B&S naming convention and lengths, but I’m a bit more confused about the heat range.

For reference, the recommendation is here:

First, the Champion J19LM has superceded the CJ8 series. So a heat range 19, about the hottest champion makes, in place of an 8. While I get it that they may have had to do some things to deal with emissions, is this really prudent for “antique” (mid-late 80s flathead engines?

Now, cross references. Take the listed Autolite 295. It cross references to an NGK B4, while the CJ8 cross references to the NGK B6S. At the same time, the newer J19LM parts cross reference to an NGK B2 plug. NGK is hotter as the number goes lower, while champion gets hotter as the number goes higher.

It seems that maybe the NGK B4 or the Autolite 295 are good compromises on heat range for these older engines. Or are we just better off running higher heat range plugs and changing yearly?

It seems somewhat overly complex and arbitrary.

I’ve seen some comments to run the coldest that doesn’t foul. But at the same time I’ve also read to burn hotter to help reduce emissions.

So what’s the best bet for older engines running modern fuel?

Autolite cross reference:

And the Champions:

 

[Gyro Gearloose]

In normal use, something moderately loaded like a lawnmower or garden tiller, either the J17 or J19 will work great. I've used both in briggs flatheads since they first became available and have never seen any indication they were too hot.

Back when the J8 was the briggs OEM plug I saw plenty of indications they were too cold. If an engine used even a modest amount of oil they would cake up with carbon. Before the J17 became available I would throw the J8 away and replace it with an AC plug because AC was available in hotter heat ranges.

 

[Lubener]

I use J-19's in all my small engines now, newer and old. They burn very cleanly.

 

[JHZR2]

Thanks. So it seems that the autolite 295 and NGK B4 would be superior to any 8 series champion plug, and the 19/b2 heat range would be better then. I had read that the 19 was a response to changes in compression and last ditch efforts to save the flathead. Mine are older so that wasn’t part of the design criteria. I’ll need to look closer at my plugs.

 

[Slick3914]

Run a J8 and call it good.

 

[JHZR2]

Run a J8 and call it good.

Is there a reason that the j8 is a better option than the hotter plugs? That is my confusion here…

 

[Slick3914]

J8’s have worked for 50 years, there is no need to over think it.

 

[repairman54]

I've been running the 19 in my old mid '90's Tecumseh flathead snowblowers with zero issues. Champ used to make a fine wire ''easy start'' branded plug, they have been in my 2 'blowers for at least 10 years now. I just check the gap and put 'em back in.

 

[JHZR2]

Right now I put a B4 in. Runs well. I’ll pull it in a few hours of use to see what it looks like.

This is the J19LM I pulled.

 

[slacktide_bitog]

Use NGK BR2-LM or Autolite XST458 (iridium). Same heat range as the J19 you took out. It looks like the appropriate heat range for your usage.

It might still be worth using a resistor

I've been running the 19 in my old mid '90's Tecumseh flathead snowblowers with zero issues. Champ used to make a fine wire ''easy start'' branded plug, they have been in my 2 'blowers for at least 10 years now. I just check the gap and put 'em back in.

Autolite still makes the iridium Xtreme Start.

 

[JHZR2]

Use NGK BR2-LM or Autolite XST458 (iridium). Same heat range as the J19 you took out. It looks like the appropriate heat range for your usage.

It might still be worth using a resistor



Autolite still makes the iridium Xtreme Start.

Why use the resistor?

The heat range thing is what gets me. The engine was designed for a Champion 8 (4-6 in NGK). The change to 19 is a much more modern situation.

 

[RyanY]

FWIW the 19 will work just fine in most applications. However I had one old Briggs that needed a colder plug to avoid overheating. This was an older unit (from 1978) with point ignition; I did not have problems with the 19 any others.