Spark Plugs - CONFUSED

[BAHNZY]

Been around bikes and engines all my life, even work in the industry, but the one think that i have never got is spark plugs and what should/shouldn't be used.

Point in case, the 84 RM125.
- According to the NGK book the 84 125 should be fitted with a B9EGV or the Iridium BR9EIX
- The OEM Suzuki parts manual references a B9EGV
- The bike is fitted with a BR8ES and a NGK TB05EM rubberised plug cap.

I have found that the bike struggles with a 9 heat range plug, hence the 8. Where i am stuck is with the resistor type plug. I've been told not to use a "R" plug yet i have been been running BR8ES without any drama's. What's confusing is that if a resistor plug can't be used, then why does the NGK site list an Iridium version as a resistor plug and the standard plug as a non "R" plug?
Should i drop back to a B8ES rather than a BR8ES?
What is the resaon that i shouldn't use a "R" plug, given that the bike is not fitted with electronic gadgetry or digital ignition?

[LWC82PE]

I wouldnt be using a garden variety  'ES' They are the most basic cheapo type, there is so much better plugs you could use and the ES was never specified for your RM. Stick with the  gold palladium, platinum, iridium etc types with the fine wire electrode. I always go with what the book says regarding type, but these days with the fuels we got you often need to ignore the factory heat range specified but alos not go too hot. I have often wondered the same thing as to why the optional iridium has the resistor but ive used them in bikes that specified no resostors and its been fine. if you want to use an 8 but not irdidium or resistor type then use a B8EGV. Some people say the EGV (gold paladium racing plugs) are crap but i have never had or seen a problem with them.

[caps 999]

non r plugs are really starting to become scarce but ive never found a differnce between a r or non r plugs and i run spares for 5 years at a bike store  you may find that suzuki offer a b8egv or an 8 heat range plug as a cold weather option in my 480 honda recomend a b8eg but i always have run a b7es or br7es because of the slowely lowering fuel qualities over the last 30 years and up and down climate in vic makes the 8 fowl in no time so going one heat range hotter ie a lower number on a ngk or a higher number on a denso will combat this and shouldnt majorly affect the engine
As for the es eg egv  and eix these just refer to the electrode es is a std electrode best for all round riding eg egv are basic race plugs lower plug life then a es but more direct spark slightly smaller electrode and eix is a needle point electrode best for full on racing with high octaine fuels and technicly they arnt designed to last longer than a race day in the normal 2 stroke

[DR]

Different strokes different folks I guess..have used the B8ES or BR8ES all my life in near all my bikes without incident. Can't say the same for the EGV range of plugs though, they've let me down more than a few times after I've decided to lash out and buy them..total waste of money from my perspective and there is no 'noticable' power gain to be had by using them

[Lozza]

Resistor is there for electrical 'noise' suppression, there is no real reason to use one unless someone says run one with a digital ignition etc etc.
Caps NGK and Denso numbering goes the same higher the number the colder the plug.My 400 quite happily runs a Denso 29(NGK 9.5) so if you need a 7 plug Caps it needs some tuning.Have had the same Denso in for about 3 years does the same on 91 pump as it does with my own race fuel.
Without running over old ground I've shown a dyno chart of how a plug made 0.5-1HP difference across the rev range, and put up the challenge for anyone to see if they can do the same in the same time it takes to swap a plug and/or for less than $50.

[BAHNZY]

I understand what the "R" is for in terms of noise suppression, what I have yet to fully understand is what difference a "R" vs. a non-"R" will do in an engine, in this case a 84 RM125.

i.e. if a rider runs a "R" plug in place of a "Non-R" what would they expect may/will happen?

This intrigues me as I have checked out many bikes of recent months and have seen a huge amount of variations. The one that got me most concerned was the 1980 RM400 that had a 5K resistor plug cap along with BR8ES. Strange when the bike is not even meant to have a resistor plug. To boot the owner said that it ran like a clock and never gave an ounce of trouble, starting or otherwise.

[LWC82PE]

Ok when i was saying that you often need to go hotter on the plugs with todays fuels, well that comes from experience with twin cylinder 4 strokes from the 60'/70's and for road use, which may not be the same situation or be required in VMX 2 strokes. Basically when we had super fuel it was fine and you could run the carby and plug settings as per the book if you had a stock engine and rode normally. Problems came when super disappeared, and many many people started experencing severe plug fouling and all they changed was the fuel to LRP or Unleaded.  No one ever said you need to re-tune the engines for these fuels. Ever since about 2001 i have re-tuned several hundred bikes to run properly on todays pump fuel and thats about the time problems started. Initially the fuel companies were saying its  not the  fuel thats the problem but then i got official documentation from BP fuels and got information from people in the fuel industry that said yeah its the fuel thats causes the differnt running conditions in certain engines. Its depends on the combustion chamber design and compression ratio and the burn temperature of the fuel and is mostly affects older 60's/70's 4T engines. What i discovered was that at low temperatures the carbon deposits were building up and not burning off. We had guys who bikes would foul up the plugs after 10mins of city or town riding at speed limits. Eventually BP said that on certain old cars and bikes you have to go one or 2 heat ranges hotter on the plug range and adjust the carby settings to get the engines to run properly with the new fuels and burn off the carbon at lower engine temps. If you really rode the bikes hard you can sometimes get away with the standard heat ranges. There is a few guys that still run the standard B8ES in twin Triumphs, but i do know from experience that you really have to rev them hard and you would not be obeying the speed limit all the time to keep the plugs clean. if you sit at the stop lights idling too much then they do foul up. Most are running B7ES or B6ES now with the carbies tweaked and now the plug fouling has dissapeared.

[EML]

Thankyou Mr LWC, that explains alot of what has been going on with my 650 Yamaha Wasp, though mostly on the one pot. I will experiment with a hotter plug and go for a rejet.