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The figure 7 represents the heat range of the plug. Usually it is unwise to deviate from specifications unless problems force choosing a different heat range. If the spark plug regularly fouls then a hotter spark plug could improve the problem - with NGK that would mean moving from 5 to 4.
Any move must be made with care to avoid the engine damage possible if the spark plug is too hot.
Hot and cold plugs, incidentally, indicate the amount of heat the spark plug dissipates from the centre to the body and doesn't affect the temperature of the engine. Broadly cool running engines need hot spark plugs and hot running engines need cold plugs so in each case the spark plug nose will achieve the self-cleaning temperature without becoming too heated.
Moving from a 5 heat range to a 7 (NGK) is moving to a colder plug so yes it will run fine, at least for a while, though you could find plug fouling might be a problem...
ngk 7112d8ha plug is a standard plug which is in the center of the heat range
you can determine the heat range of any plug by looking at the ceramic insulator inside the plug
if the ceramic is shallow or close to the end it is a cold plug --for use in hot running engines
what you have will have the ceramic insulator a bit further down inside the plug -- normal engine operation
and hot where the ceramic insulator goes well down into the plug body-- use for fouling engines and oil burning engines
the rating comes from the ceramic ability to transfer heat away from the plug electrode
for stories on plug heat ranges , go google and type in-- spark plug heat ranges and explanations --
I would definitely go with an iridium plug offered by NGK for the most complete combustion which increases engine efficiency, fuel efficiency, and power. The part number for an NGK iridium spark plug for a Yamaha dragstar is DPR7EIX-9. These are a bit more expensive at around $7 but are absolutely worth spending the extra money as they are proven to last significantly longer. If cost is a factor, a regular ngk spark plug is around $2 and would be part # DPR7EA-9. I hope I've answered your question satisfactorily and ask for you to take a moment to rate my answer. Thank you, Jim. NGK 7803 DPR7EIX 9 Iridium IX Spark Plug Pack of 1
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g
k r = resistor b=thread size = 14mm z 7 = heat range - NGK, the lower the number the hotter the plug. Other mfg. are opposite - higher number=hotter h = thread length =1/2"
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-10
These are THE important ones... the rest are mfg. specifics
For most riders the standard (hotter CR8EH-9) spark plug is the best choice. Most cycles are set up for sea level running and on the rich side for longevity of the motor. As you move higher in elevation the thinner air makes the cycle run even richer. Vacuum carburetors and EFI systems on Honda's compensate for most of this , but a colder plug can be progressively more prone to fouling under these conditions. If warm temperature, long distance, and high speed running (combined) is your style of riding, then the colder plug (CR9EH-9) is probably a good choice for you. I do a lot of long distance riding in the heat of summer and have never felt the need of the cooler plug. I do recommend that you carry a second set of plugs in either case, just in case you foul a spark plug (I carry my old plugs that still work). The plugs you use may not be readily available unless the rare fouling of a plug just happens to be next to a Honda dealer. There is a relationship between temperature and plug heat range. If you had a sidecar and liked to drive around in 30 degrees F you might find the cycle started better with a CR7EH-9 (At 100 degrees F you would probably melt a hole in your piston with the CR7EH-9 installed).
The numbers 4 and 8 are heat ratings. The lower numbers run hotter. Different heat ratings allow you to choose the best compromise between keeping the plug from fouling and making the electrode last longer. If your plugs tend to foul, you need a hotter plug. If they tend to fry away, you need a cooler one. As engines get old, they tend to need hotter plugs. The differences in the heat ratings can be seen in subtle differences in the dimensions of the electrode (usually the center one) and the little insulator around the center electrode. The dimensional changes effect the heat transfer characteristics of the plugs, which changes how effectively the high temperatures present at the spark are conducted away. Besides the heat rating of the plug, the other big factor is having a nice clean thread surface in the engine block, which is why some mechanics will use a thread chaser when changing plugs. Here's a link to NGK's numbering meanings
http://www.ngk.com/sparkplug411_manufacturer.asp?manufacturerID=1
I hope you found this helpful.
32 to 1 is the standard mix. That is 4 ounces two stroke ENGINE oil per gallon. The brand doesn't really matter. Don't use MOTOR oil in the gas. The stock plug is NGK brand, R6918B-9. I would suggest a hotter plug, R7376-8. The last digit is the heat range. The lower the number, the hotter the plug.
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