Topic: which plugs for 750?

[Tugboat]

The manual says standard is D-8ES, but lists as optional the D-7ES & D-10E. What's the difference? Is one more optional than another?

[Inigo Montoya]

d8ea supersedes the d8es.

[dhall57]

Tugboat, I have a 76 CB 750 that I bought several months ago. The plugs that the PO had in it were autolite. Im no Honda expert, but for the classic bikes like ours most recommend NGK. One local Honda dealer try to sell me a resitor plug NGK DR8ES, but later found out with a little research you don't run resitor plugs in these bikes. Another Honda dealer told me the original  NGK D8ES plug was a discontinued # and what replaced it was NGK D8EA. These work fine, seem to run much better than with the autolite

[Gordon]

The D7 is one step hotter than the D8.  I run D8 in my 750 in the Summer and D7 in the Winter.  It starts and idles much better when it's cold with the D7's. 

[srust58]

I still have the original set that came with my 76F.  ND X24ES.  I have the D8's in now.

[DukieFrankenkit]

I am running the same as Gordon D7EA for the winter but I use the ND X24ES when the weather gets above 40 and stays there.
 

[Deltarider]

Originally it was NGK D8ES-L. The D8ES is just 1/2 a step colder. I'm not sure whether it is the D8ES-L or the D8ES that became superseded by the D8EA. Maybe someone else knows. 

[HondaMan]

Originally it was NGK D8ES-L. The D8ES is just 1/2 a step colder. I'm not sure whether it is the D8ES-L or the D8ES that became superseded by the D8EA. Maybe someone else knows. 

The 1969-'71 plugs were D8E. Then Honda asked NGK and ND for something that would foul less while not adding the heat that the D7E did: the result was first the NGK D7ES, which was the D7E with a superior insulation seal to keep it from burning itself out a highway speeds. It was a great improvement for town-ridden 750s. Soon after, the D8E became the D8ES, too, with the "S" denoting "super wide heat range" on the NGK boxes.

In 1970, ND, who is the parent company of NGK and who made mostly auto sparkplugs, got into the fray with their own plugs. They had long sold the X24E, which was equivalent to the D8E, but with a thinner center electrode: we racers liked these at the time because they ran slightly hotter that the D8E, and cost 1/2 the price.

In 1971, at Honda's request, NGK introduced the D8ES-L, which was the D8ES with an extended tip to burn off deposits. It was a really good thing, and helped with almost all of the 750s. The hotter tip stayed cleaner longer, and the heat range was approximately like a fictitious D7.8ES might be: just a little hotter, but not too much.

In 1971, ND introduced the "Hot U" series, which I thought was just an advertising gimmick: they made U-shaped (like a C-channel) ground electrodes and put them on their plugs. Pundits said "it makes room for a bigger spark". Turned out, they and I were dead wrong: they had also "warmed up" the plugs by making all of the "Hot U" plugs with an even narrower center electrode and also extended it even more than the D8ES-L tips: the result was immediately recognizable if you slipped a set into your 750 or CB500. The midrange was stronger, the MPG better, and the plugs stayed cleaner: a true trifecta for this bike. We stocked both the NGK and the ND, but never could get enough of the ND after word got out. the ND number is X24ES-U, with a heatrange equivalent to a fictitious NGK D7.6ES (or -EA).

Then they introduced the X22ES-U, aimed squarely at the CB500. Same story: another success. This plug is about the same heat range as an imaginary NGK D7.25ES, and was perfect for all but fast, all-out touring in those engines: we installed the X24ES-U in the 500 for that faster and all-day touring service, with excellent results.

The ND is still available today, and it is the first choice in my bike. I regularly clean and re-use them: some of mine date back to 1982, and work perfectly still. I run the X24ES-U in all summer riding, touring, and high-speed chasing, and the X22ES-U in wintertime so the engine warms up a little faster in commuting use.

The NGK designations began as "D8E" or D7E", and there was a "D9E" and D10E" until 1971. Then they all became the "S" series, like D8ES, which meant "super range plug" or wide-heat-range plug. This just meant they would not burn out if subjected to overheating, and it was true: the D8E could be burned out in 100 MPH touring on the CB750 at the time (I burned them out regularly in both my K1 and my present K2), while the "S" plugs survived it. The D9E disappeared with the "S" series.

When the Dems dropped the national 55 MPH speed limit on the nation, the D8ES would not stay clean, even in 60 MPH touring: that's when the quest for something better made all the above items happen. The D7ES would burn valves if toured all day, and 12-hour day rides were not uncommon, just to get somewhere at 55 MPH. The X24ES-U solved all of that. 

[Deltarider]

Excellent contribution! What Hondaman describes runs parallel with my experiences, be it that mine are limited to the use of the 500 Four. For my purpose I prefer the X24ES-U too, but, alas, can't find it in the shops anymore. A shame, because it was the better plug.
What I haven't discovered yet: is there any difference in (tip) design between D8ES-L and D8EA and D7ES and D7EA respectively?  

[Retro Rocket]

So, what plugs would be better with a hotted up 750 motor with higher compression and in a hotter climate, {like Texas i have been told}.?

Mick

[Inigo Montoya]

Most end up using a d9 plug.

[Kevin D]

I have two seasons, 5000 miles on my stocker with these ND's and I like 'em.

http://www.densoproducts.com/resultsAppOther.asp?otherMotiveID=58437&mfid=3

[HondaMan]

Excellent contribution! What Hondaman describes runs parallel with my experiences, be it that mine are limited to the use of the 500 Four. For my purpose I prefer the X24ES-U too, but, alas, can't find it in the shops anymore. A shame, because it was the better plug.
What I haven't discovered yet: is there any difference in (tip) design between D8ES-L and D8EA and D7ES and D7EA respectively? 

My understanding of the "A" suffix change was this: the U.S. EPA warned NGK of making plugs with "too wide of a heat range", meaning that plugs that could run cold and emit high hydrocarbons, but then burn them off (by blowing off the carbon) to preserve the plug's performance if the engine was revved higher at a later time, "might become illegal in the United States". This 'threat' occurred during the Clinton Administration, when that ass#$!e gave almost unlimited powers to the U.S. EPA in return for "green" contributors to his $$ coffers. It meant nothing, but it made NGK revert the plug designs back to a more standard heat range (i.e., narrower), much like the original D8E/D7E designations. This also caused the demise of the best spark plugs for FORDs, the Motorcraft design, which was similar to the "S" series NGK plugs. In the end, the 'spin' put on this change was that the "A" plugs were "more tightly controlled heat ranges, for anti-pollution reasons" (this was NGK's answer in a letter I saw from an interested party who wrote them in 2001).

It was yet another worthless political move to force an "emissions" change so small as to be 100% immeasurable, yet make a politician look good to his supporters.

Honest. You can check this one out yourselves, if you wish: trace back to the end of the D8ES / B8ES, etc., series plugs, on other forums (like for Japanese cars, which typically ran B6ES or B5ES plugs), and you'll find the irritated stories from the late 1990s...

The ultimate result: the D8E is too cold, which was true from the beginning, in these lightly-loaded engines. The D7E tends to run pretty hot in the 750 because of the undersquare stroke design: it heats the exhaust valve a little more than an oversquare design. Getting a heat range in between was always the key to good all-around performance on this engine.

The X24ES-U and X22ES-U can be bought at Sparkplugs.com: I buy them a box at a time for my customer's tuneups. Other places sell them a little cheaper, but often are also out of stock.