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Discussion Starter · #1 ·
Have you guys ever used a spark plug that is hotter or colder than the original? What were the results?
 

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Did it all the time on cars. Never done on a motorcycle. I really have no idea if I did any longer term damage but I can see now where I sure could have. Cars always ran much better. But that was in the days of points and condensers and adjusting timing was by ear and test runs.
 

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Have you guys ever used a spark plug that is hotter or colder than the original? What were the results?
Going with a colder plug during the summer months, should cause no harm. It might foul the plug with a lot of stop and go, and idling. It may be better for WOT for long periods.

A hotter plug could cause problems, for prolonged high speeds. It might be better for winter riding, and stop and go stuff.
The potential to do harm, is greater with the hotter plug. I would be hesitant to use them. If the engine is old and has low compression, which causes the plugs to foul, then you do not have much choice.

Using NGK plugs makes understanding the heat range easy. Generally a number 6 will be as hot as any manufacturer recommends.
A number 12 might be used in a track bike. For most street applications, a 7, 8, or 9 will work. But check the book. I am generally wary of a or hotter, if I am doing anything except around town puttering.

Going back to your question. You did not mention what type of engine is being used. Street bike, dirt bike, 2 stroke, 4 stroke, or how many cylinders.

UK
 

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My daily driver car caught fire back in late 2016. It was put out in time, but the result was the engine only ran on a single cylinder. Even after I cleaned up all the fire damage, the best I could get it to do was somewhat run on two cylinders. Then I got the idea to run spark plugs of a higher heat range than stock, thinking maybe the higher heat would burn off any excess carbon buildup? I don't know, but after a few months of running the plugs the car ran like new again.
 

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Discussion Starter · #5 ·
UK: Honda CB 400T1 Street bike. 2 cylinders, 4 stroke, and yes, right now I'm using the original NGK 8 (NGK D8EA)
 

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UK: Honda CB 400T1 Street bike. 2 cylinders, 4 stroke, and yes, right now I'm using the original NGK 8 (NGK D8EA)
Sweet.
That sounds correct to me.
One of the XS1100 Yamhas has NGK 7 as stock. I switched them to 8 which I am more comfortable with. I do remove and check tho. Easy enough on the older Yamahas, but an all day job on the newer Suzuki and Triumph. Can not even see them.

Once upon a time, long ago, we would start the Yamaha 250 2 stroke screamers, on a number 8, and switch to a 10, 11, or 12 before going on the track. Run a couple of laps, kill the engine after a WOT run, and check the plugs.

The drag strip and track guys, cages or bikes, are doing the same.

UK
 
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