most look something like this

The ones I saw the harley guys bichin bout had to use a screwdriver behind the wire to remove the resistor.

Boy this thread got out of hand quick! lol. Easy there boys..........
The hotter BP6 plug was most likely in there from when the wet side seal was leaking, looks like it was oil/fuel fouled at the change. Put a hot plug it and just test it, the bike won't stay running now and the hotter plug may let it and help you solve the prob.......you WONT HURT IT.
Again though, eliminate any unnecessary resistance by not using an "R" plug......your plug cap is an aftermarket unit, would be a good idea to replace it (OEM not ness here, a good "resistor less" replacement from any bike shop would do ok) just to eliminate any variables .
Another thing I do when I'm diagnosing a possible weak ignition is to use a B8EG racing plug.......not because it's anything fancy but just because it's smaller center electrode gives the ignition a slightly easier job of jumping the plug gap. If NGK made BP type non "R" plugs like a BP7EG I'd be the first in line to buy....lol.
Good luck,
--Ray

Yes, that's normal. Those are manufacturing lot numbers and vary.

It's probably obvious that I don't agree with a lot of the information posted in this thread. And while I'm going to continue to "live dangerously" and not worry about gapping used plugs... I'm not brave enough to try "projected" plugs or significantly different heat range plugs (especially hotter) in a stock engine.

(The advice to use fine wire plugs- of the same heat range -is correct in that they require less voltage to fire and tend to be less prone to fouling.)

Here is some advice from NGK:

"We’ve discovered a large number of consumers rely on information provided by way of tech forums.
While tech forums can be useful tools, a lot of erroneous information is written in these forums. Who
knows their product better than the manufacturer? .......contact our technical department at
(877) 473-6767 option #2 or visit us at www.ngksparkplugs.com"

The photos you've posted all look to me like fouled plugs. In my opinion a hotter or fine wire plug is not going to "fix" the underlying problem. And I'm personally not sure what troubleshooting value trying a hotter plug will have... but again, that's not a route I've ever taken so I'll withhold further comment.

I'd go back to basics. How's the compression? Pressure (and vacuum) test the engine to rule out air leaks. Is the carb stock with the stock jetting as a starting point? Float level? And probably the most important on your bike and maybe the first thing to check... condition of points and proper ignition timing! It could be as simple as the timing has retarded itself due to wear and tear on the points.

I hope you find the problem soon!

Forgot one thing... air filter. It can look clean and be properly oiled but not flow enough air. The foam can deteriorate over the years. Over-oiling especially with the "super sticky" air filter oils can also cause a problem.

I wonder if there may be some oil left behind from the bad seal fouling them.i do not think air leaks would do this but make it run lean.

Checking for air leaks is a basic test I've learned by experience is a good idea even on a newly assembled engine. You are correct that it is not the most likely cause for this problem... but still something *I* would check.

As far as an air leak not being a possibility? Below is a picture of a case half from a 1978 DT175. Ran pretty good but the thing was oiling plugs like crazy even with a new seal installed. A pressure test revealed that the factory sealed areas (probably a remnant of casting in the steel inserts during manufacturing). were leaking like a sieve and the transmission oil was being sucked into the crankcase. This would never have been found without a pressure test.

(In about 1979-1980, Yamaha changed their manufacturing process and these little sealed areas were no longer there... they must have realized it was a problem.)

Betting my money on Mark T to win.

It continues to amaze me how much knowledge the collective on this site possesses and is willing to share! I consider myself somewhat knowledgeable about these old bikes, but leans something new every time I log in!


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Thanks for your interest Mark your opinion is important for me.

1) I agree that using a different plug wont solve the problem thats why im willing to find the problem to fix it but ill try the plug without the ''r'' and a new cap without resistor
2) I might contact ngk about this but im sure the problem isnt their product its a problem with the bike and im not sure they could help with that.
3) The plugs sure look a bit black , but if i have a chance today im going to post a picture of the plug of my Rm 250 and im sure its way more black than this and it still doesnt have spark plug problems. Im sure something goes wrong Inside the plug somehow and im sure its not the deposit on the electrode that is the problem, because even if you clean the plug as good as you like, it still dont work.
4) Im guessing the compression is good since the bike generally starts in one kick and is able to lift its front wheel in 2nd gear on power only without me pulling on the handlebars, i dont have a compression gauge at the moment, because mine doesnt work anymore. I should get a new one soon.
5) Indeed a pressure test would be a good idea.
6) Its got a stock carb with stock jets. I dont remember the numbers but i do remember that i checked it last time i cleaned the carb. float level is perfect indeed since ive worked on dozens of carbs before and i set it myself.
7) I never checked the points and/or timing because as i mentioned in a previous comment , ive only worked on never motorcycle with CDI ignition system and even if i know how this older system works, i didnt wanted to disturb it since its working fine (i think) although, how could i check the timing? Timing sounds good to me because the bike doesnt ping and has good power but its true that sometimes it kicks back when i crank it so perhaps the timing would be advanced a little? Is that possible on these older bike? never seen that happen on a newer ignition system other than broken flywheel key?
8) it hasnt got a weak spark since the spark on this bike is stronger than my Rm 250 and the Rm dont have spark plug issues.
9) i dont run an air filter at the moment because the old one was coming apart and i didnt want pieces of filter in my carb (it had lots of pieces into it when i cleaned the carb) So the air filter cant be the problem since it hasnt got one Dont worry, i only test drive this motorcycle on pavement since the dirt trails around my house are for motocross only, no enduros. They are no good in deep soft sand.

Nice,Mark
I have to ask though as I can not believe the manufacturer released this info and open themselves up for recalls.
And since you are such a fanboy of only taking the manufacturers marketing hype as gospel "facts"
And since you take no stock in user groups such as ours,I ask
"Where did you read this ? On the internet?"
But seriously,
How though does that oil leak show up on a pressure test? You would seem to have to have the side cover removed or it would hold pressure would it not?Also your idea of a red hot spark plug tip igniting fuel is bogus as it takes an open flame to do so.unless under very high compression ,very much higher that our 2 strokes.Yes you can actually douse a lit cigar in a bowl of gasoline.And carbon is not the gooey crap on a BBQ or in a used exhaust pipe,all you are burning off is the unburnt grease and oil,the carbon is the soot that is left behind.