# Spark Plug Gap



## mk033 (Nov 16, 2013)

I have following Murray Blower:

Murray Blizzard Model#: 629108X84A
Manufactured Date: 2003 10 080
Serial Number: 753 1428131N215
Tecumseh, 10 HP, 4-Cycle Engine
Electric Start, 2-Stage, 29” Width & 21” Height

I would like to replace the spark plug and unable to find any information relating to the matter in the user manual. Spark Plug that is on the engine is AJ19LM. Would anyone know the proper GAP for the plug?

I do not know if the GAP of a plug is an plug dependent, engine dependent or snow blower(machine) dependent. Any information would be greatly appreciated.


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## oneboltshort (Dec 16, 2019)

Engine dependent

http://www.lausonpower.com/CustomerService/BSI.pdf


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## Toro-8-2-4 (Dec 28, 2013)

You have an RJ19LM. The R is for resistor. You could also use a non resistor J19LM.


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## Rooskie (Feb 12, 2015)

Wisdom gleaned over the years:
'.030 seems to be the number to use if one doesn't know for certain.'


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## JLawrence08648 (Jan 15, 2017)

Looking at that chart, it seems RJ19 or J19 are used for all Tecumseh engines used for snowblowers.


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## Ziggy65 (Jan 18, 2020)

The H40-80 and HS40-50 engines use RJ17LM


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## JLawrence08648 (Jan 15, 2017)

Yes I saw that. The xxSK Snow King engines use the J19 plug which is a hotter plug than the J17. The xxSK are used exclusively in snowblowers where as the H and HS were a utilitarian engine used in summer and winter applications thus the J17 plug which one can construe as a summer plug. Later in years when the xxSK Snow King engines came out the recommended plug was now the J19. I'm assuming because the cold weather keeps the engine running cooler than an engine in 90° weather they want you to use a hotter plug. My feeling is many times a lawn motor engine is running at 2,500 RPMs while a snowblower engine runs at 3,600 RPMs, you don't need a hotter plug to burn off the carbon because of the faster speed. If I had to keep one plug in my tool box it would be the J17 but I have both.

This past week there was a discussion on spark plugs for Chinese engines. ST1100A recommended using a hotter NGK plug for snowblowers, a BPR6ES rather than the summer plug BPR5ES. IMO either will work though I do follow the same thinking.

If you have a piece of equipment that does a lot of idling, or running at low RPMs, the hotter plug would be a better choice.


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## Ziggy65 (Jan 18, 2020)

JLawrence08648 said:


> Yes I saw that. The xxSK Snow King engines use the J19 plug which is a hotter plug than the J17. The xxSK are used exclusively in snowblowers where as the H and HS were a utilitarian engine used in summer and winter applications thus the J17 plug which one can construe as a summer plug. Later in years when the xxSK Snow King engines came out the recommended plug was now the J19. I'm assuming because the cold weather keeps the engine running cooler than an engine in 90° weather they want you to use a hotter plug. My feeling is many times a lawn motor engine is running at 2,500 RPMs while a snowblower engine runs at 3,600 RPMs, you don't need a hotter plug to burn off the carbon because of the faster speed. If I had to keep one plug in my tool box it would be the J17 but I have both.
> 
> This past week there was a discussion on spark plugs for Chinese engines. ST1100A recommended using a hotter NGK plug for snowblowers, a BPR6ES rather than the summer plug BPR5ES. IMO either will work though I do follow the same thinking.
> 
> If you have a piece of equipment that does a lot of idling, or running at low RPMs, the hotter plug would be a better choice.


You are bang on. 

I just checked my spark plugs for the 1968 Ariens with the H50 and I am running the hotter J19 plug. 

For most of it's life it ran a Champion J8C


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## JLawrence08648 (Jan 15, 2017)

The J17 and J19 are an improved plug over the J8. I remember reading there was some type of problems with the J8, I believe it was fouling, the J17 & J19 supposedly that problem. They are slightly hotter than the J8 or the smaller and famous CJ8 used for weed wackers, chainsaws, and hand blowers. This slightly hotter J17 & 19 reduced emissions which was welcome.


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## Toro-8-2-4 (Dec 28, 2013)

With NGK the lower the number is hotter. With Champion and Bosch it is the inverse of that, the higher the number the hotter. For example the BPR5ES is the hotter than the BPR6ES. The J19LM is hotter than the J17LM I hope this chart is helpful.


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## mk033 (Nov 16, 2013)

Thank you so munch for the information. I guess I got more than I asked for.... lol

Reading through other related posts, now I would have ask few other question to experts. What is resister do and why some don't have resister on them? Second question; when plug runs hot, what variables does it adds to the engine/performance? What difference does the different gap makes for the spark plugs?

It seems that if you use a platinum plugs, you may never have to replace them, it seems.


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## JLawrence08648 (Jan 15, 2017)

Resistor plugs came out in the 60s to prevent radio interference. It was so bad you could not hear the radio just a tat tat tat. Now you use resistor plugs for the same reason but also as not to interfere with the car's computer, cell phones, electronic devices. 

A hotter plug burns the carbon off the valve heads and piston heads, too hot a plug will burn a hole in the piston head, ...

Too small a gap you will have a weak spark that may not fire the gasoline. 

Too large a gap takes more power, electricity, to fire the plug however you have more space to explode the gasoline and will have more power. Racing cars have a larger gap but they add a high intensity ignition system to compensate. 

You can use platinum and iridium plugs in small engines as long as they are the equivalent. In a car I use platinum unless the manufacturer calls for iridium. Iridium plugs wear down the center electrode fast and periodically need to be removed and gapped.


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## Rooskie (Feb 12, 2015)

Ziggy65 said:


> You are bang on.
> 
> I just checked my spark plugs for the 1968 Ariens with the H50 and I am running the hotter J19 plug.
> 
> For most of it's life it ran a Champion J8C


My 1948 Mercury outboard runs a J8C, as well.
Popular plug.


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## carguy20 (Feb 8, 2021)

If it were me, I would simply stick with the plug that is specified either in the owner manual or other literature. My toro takes an NGK BPMR4A plug (RCJ8Y is the equivalent). I don't see the point in trying to put in a performance plug or something like that. It is a piece of power equipment, not a race car. 

I got the machine for free because it "wasn't working". It was hard to start and did not idle well. I had picked up the Champion plug planning to change it, but when I took the NGK plug out that was in it, it looked ok. Then I checked the gap, it was .022. When I adjusted the gap to .030 (perhaps SLIGHTLY larger, maybe .031). After reinstalling the plug, all I need to do is choke it, prime it once, and it starts on the first pull every time. If I shut it off and then restart it, I don't even need to prime it, starts right up.

Main thing, using a proper plug and a proper gap will give you years of trouble free use.


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