SPARK PLUGS FOR 650 CSR

Information relating to the Matchless G12 or AJS Model 31 650cc twin
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Re: SPARK PLUGS FOR 650 CSR

Postby Rob Harknett » Thu Dec 26, 2019 5:14 pm

JEAN-NOEL wrote:Thank you all for your skilled advices ! I realize I had missed the excellent Mr HARKNETT job's...Very interesting. So Spriddler's post regarding counterfeits.
Just checked what are my sparking plugs : N3C, very prone to fouling on the left cylinder and both are sooty.
I have inverted the plugs to see : there is always a problem on the left side. The mag has been fully refurbished.
I will try N4C or B7ES to see if there is an improvement. And I will investigate around the carb to lean the mixture.
My engine is not yet runned in, and I don't exceed 3000 RPM and max 1/3 throttle, so it is difficult to deal with the main jet or the needle. My carb is correctly setted according the manual : n° 4 slide, 4th notch, 450 main, 20 pilot, 0.106
It is also interesting to know that some users fit hotter N5C on their CSR with no problems.
Kind regards. J.N.

Not really down to me Jean- Paul, I simply conducted a survey, the results of which came from members. When the survey had run its cause. I believe it was Eamonn that warped the results up in a PDF file for publication. May had been me then Eamonn edited and published a better than mine PDF file

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Re: SPARK PLUGS FOR 650 CSR

Postby JEAN-NOEL » Sun Dec 29, 2019 10:26 am

Don't be too modest Rob, you had an excellent idea, which has been materialized.

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Re: SPARK PLUGS FOR 650 CSR

Postby Groily » Tue Dec 31, 2019 10:44 am

Interested to read all this, and see the comments about the NGKs.

I don't doubt anyone's experience for one moment, but my Mod 31 with 8.5:1s has run on just the one set of B8ES for 12K miles and they are still quite OK to look at (I had them out only yesterday). I have exactly the same carb jetting etc as you do Jean-Noël, with a not very old 389 Monobloc.
And my Mod 20 does about 5 years or 20K miles a pair on B6ES or B7ES. In the past I've run N5 or N5C Champions in that one too, with no probs either.
I have only ever had one NGK fail, and that was in my 650SS Notrun, which seems to be more sensitive to plugs. Twin carbs, different head design, or what the heck?

It seems a bit hit and miss, so I must be lucky because I think of plugs as 'fit and forget' on my AMC twins. The short-reach B6HS NGKs on my A10 have been in there for no fewer than 10 years and a good 40K miles, which must also say something I suppose.

I think you're right that N3 is just a tad cold, or 'hard' for these engines. And therefore they get a bit sooted. On my 650 the right side is the one that is always a little bit darker. But it runs very cleanly and never snuffs itself out.

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