Need a hotter plug, what kind should I get.

I was told by some of my dads friends that race dirt bikes and jet ski's that when running a high compression head with race gas that I should run a hotter plug. I am still running the standard plug from 1975, they said I should get a NGK R but I do not know what #. Do you have some kind of idea.

Re: Need a hotter plug, what kind should I get.

chuck russo va /

call a moped shop in your area, one that deals with older peds not just the new ones.

Re: Need a hotter plug, what kind should I get.

Try this link

You have to be careful about hotter plugs, depends on how much you use your moped and if it is a bunch of short hops or long trips.

The lower the number the Hotter the plug, for example NGK B5HS is a pretty standard plug for most mopeds. Grandes use NGK B7HS.

Also read this link on how spark plugs work, the part about Hot and Cold plugs

thats bull

That is the problem with about 80% of what you gear about motors... people get their facts wrong.

When running motors built for more performance... you generally need a COOLER plug... not hotter.

If we assume you built it to make more HP... and that you are USING the greater HP.. (as in running it hard)... then cooler is the right way.

Going hotter can cause a hole to be melted in the top of your piston right under the spark plug.

...... been there done that ......


... NGK plugs get cooler with a higher number.

... Champions get hotter with a higher number.

Re: thats bull

That is funny because I use to race a 1996 seadoo xp fully built with forged pistons and everything on it it would do 68mph at about 8400 rpm and we had to get hotter plugs because it was running a little rich and we were running around 40:1 mixture also. We experimented with all kinds of plugs, and the word around on the circut was hotter is better. That is why I thought I needed hotter plugs.

Re: Something else

A SeaDoo is water cooled and mopeds (except Odessey), are air cooled.

Watercooled engines are more tolerant to temperature variables.

Aircooled are gone by the time you realize something is wrong.



OK ..... can you tell me what plug you were using before mods... and what plug after mods ?

No. Thats bull

Ron Brown /


After that, tell Fred the serial #s of all the dollar bills in your pocket without looking. : )

Other than general interest, it does not matter what the number of your plug was. What matters is that you had a problem which dictated using a hotter plug. You did and it worked. Trying to second guess whether that was the "correct" solution without the engine to play with is bullshit.

Casery, if your ped wants a hotter plug, it will "tell" you, just like your bike did. It will also tell you if the plug you put in is too hot. Maybe in a way you will not like.

Read Zippy's links until you understand them. You will then know as much about selecting plugs as anyone on this forum.


its bull alright


... but you don't know thw plug he put in was hotter... you are taking his word for it.

There is so much misinformation about this crap that I don't believe any of it.

I would only believe it when he tells me the numbers.... and its only a 1 digit number Ron... I doubt he has Alzheimers yet.

(thats if he even did the plug changes... I bet his dad did)

Besides... a fair number of people think "hotter" plug means a high performance plug of some sort... they have no idea what the term means.

even Don-Oh insists on calling them 'higher... and lower' heat ranges.... which is meaningless.

"higher" number ?... or "higher" heat ?... (not the same thing)

Give me the facts boobalah......... the rest is all bullshit.

Re: thats bull

Ron Brown /


Given this statement in his post:

>we had to get hotter plugs because it was running a little >rich and we were running around 40:1 mixture also

I am guessing that a colder plug would have fouled. I think in this case, if they could not solve the mixture/oil fouling problem for some reason, then a hotter plug would reduce fouling.

I also found from another of CASEY's posts, that he is suffering from an over rich mixture on his ped. I pointed out that a hotter plug is not a solution for a rich mixture, although he may have some friends who think so.


its a cow

... with testicles right ?

sorry... because of bad communications and misunderstanding of words and terms...

... I would insist on hearing the spark plug heat range number before drawing any conclusions.

(not that I care... I said my piece)

I think you forget you are dealing with kids Ron.

Re: its a cow

Hey Fred first of all i am not a kid. I may be to some 70 year old retired man sitting at home working on mopeds all day, or sitting their reading mopedarmy post all day, I am actually 21. I sit at work and I check numerous sights all day long. I can not look up the plug numbers right now at work, and it is at my dads house mostly but right now it is at St.louis power sports having a new umi throttle being put on. I can not keep it in my apartment or my dorm at school cause space is limited, you know.

Re: thats bull

I have a perfectly circular hole on my piston, right undet the spark plug on my puch. It looks like it was made to be there. it doesn't go very far into the piston.. it is more of a depression than a hole. Is this supposed to be there or is this bad.

holed piston

If its what I think it is...

It is a 'hole' that didn't melt all the way through...

(right under the spark plug)

It wasn't put there by Puch... it is the result of things getting too hot... and the top of the piston started to melt.

.. either the ignition was too advanced.

.. or the spark plug was too hot of a heat range.

.. or it was burning some sing some real low octane gas.

.. or it was too lean

.. or... there was some reason the engine couldn't cool itself.. (like mud caked all over the head).

It usually happens when one of the above is present... and the engine is being run hard.

Its no danger now... if it runs good you are fine... but if one of those factors returns... it will finish melting thru.

Re: holed piston


the sentence..

.. "or it was burning some sing some real low octane gas."

was supposed to be...

.. " or it was burning some real low octane gas."

Re: holed piston

Well, I've seen a couple pistons that are just machined that way.... was it that way new? is it exactly in the center, like it was machined there, or is it from heat? Heat can't really make a perfectly round divit, I think. If you can, check the back side of the piston for deformation, And if you didn't want to take the engine apart, you shouldn't have mentioned it, Toehead.


That little dip in the Pistons.

Reeperette /

For the record - YES, some of them do come that way, why ?

I have no idea.

But for a fact, most A3 Pistons that I've bought did, and some Puch pistons I believe do as well.

BUT, make very sure of that cause I have seen a damn fool with a speed kit get a blowthrough on a piston using a Splitfire plug before, which I didn't believe till he brought it to me so I could see it.

If yer in doubt, ask someone who carries the part to look at it and then tell you if that dip is supposed to be there or not, then crosscheck with another shop.

I say crosscheck cause recently I've run into loads of parts guys who do not know a damn thing about Tomos engines, yet pretend to, and try to tell me things I know for a fact ain't true....especially when the "nonexistant" part I am askin about has a Tomos Part # in the service manual.

So always doublecheck what your parts guy tells you.


Re: Need a hotter plug, what kind should I get.

Hey Zippy,

You say a BH7S is good for the Grande. I'm using a BH6S. Is that bad?

Re: That little dip in the Pistons.

well, it is perfectly rount, perfectly in the center, and very neat. i think it is supposed to be there, after i saw that my chainsaw has an identical little hole thingy, and it's brand new. :)

Re: holed piston

also, the back of the piston is fine, with no deformation from intense heat.

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