Honda-SOHC

SOHC.co.uk Forums => CB750 => Topic started by: Graeme77 on July 17, 2011, 02:47:47 PM

Title: Spark plugs
Post by: Graeme77 on July 17, 2011, 02:47:47 PM: Just a quick question about plugs.

First of i have dr8EA in it at the moment, but i also have some of the recomended DR8ES.

Whats the difference?

Also, long or short plugs? My factory manual suggests both were used over the years but it doesnt say which ones for the F engine (presuming my engine is origional, engine number starts 25 i think, can check if needed.

It has long plugs in it at the moment, if these were wrong would they be clipping the pistons?

Its a 1976 F but who knows whats been changed.
Title: Re: Spark plugs
Post by: Spitfire on July 17, 2011, 04:27:24 PM: The plugs for the CB750 are NGK D8ES-L (LONG) however these are no longer available, I tried several including the DR8ES which was not very successful.
So I took Hondaman's advice on the US site and fitted ND X-24ES-U, these work great,
http://www.camskill.co.uk/m18b0s1387p0/NGK_Spark_Plugs_and_Denso_Sparkplugs_Denso_Spark_Plugs_-_X (http://www.camskill.co.uk/m18b0s1387p0/NGK_Spark_Plugs_and_Denso_Sparkplugs_Denso_Spark_Plugs_-_X)
http://forums.sohc4.net/index.php?topic=77832.msg872695#msg872695 (http://forums.sohc4.net/index.php?topic=77832.msg872695#msg872695)

Cheers

Den

PS Just checked the handbook that came with the bike and the spec is for NGK D8ESL or ND X24ES
Title: Re: Spark plugs
Post by: Graeme77 on July 17, 2011, 06:39:15 PM: Ok, my factory manual doesnt mention the L except for late models. It also says the plug should have a 12mm reach, the L has something like 20mm reach (from washer to electrode).

Thats why i wondered, the factory manual suggests short for anything up to about 75/76, long for late k series, but doesnt specify which for a F.

Just thought, the R means its resisted right?

I have electronic ignition with 5000 ohm caps, does that make any difference?
Title: Re: Spark plugs
Post by: SteveD CB500K0 on July 17, 2011, 06:55:00 PM: If you have resisive caps you don't need resistive plugs (and vice versa)

If you are running electronic ignition it probably won't matter, but the alternators on these old bikes were barely up to it in the 70's (when radio interference didn't matter!)
Title: Re: Spark plugs
Post by: Spitfire on July 17, 2011, 07:48:08 PM: The CB750F/K6/K7 sections (Supplements) of the CB750 Shop Manual from those nice people at Honda specifies NGK D8ES-L or ND X24ES plugs for the CB750F/K6 and K7.
You can download the supplement here.
http://www.honda4fun.com/man_officina/man_officina.html (http://www.honda4fun.com/man_officina/man_officina.html)
http://www.hondacbfour.com/download/man_officina/pdf_manuali/CB750_K-F/CB750_6.pdf (http://www.hondacbfour.com/download/man_officina/pdf_manuali/CB750_K-F/CB750_6.pdf)
And here's the Handbooks
http://www.honda4fun.com/libretti/libretti.html (http://www.honda4fun.com/libretti/libretti.html)

Cheers

Den
Title: Re: Spark plugs
Post by: Graeme77 on July 17, 2011, 09:02:26 PM: Great, thanks folks :)
Title: Re: Spark plugs
Post by: Yoshi823 on July 18, 2011, 02:25:36 PM: The 2009 NGK catalogue specifies these details...

CB750-K1-K2-K3-K4-K6-F1...standard plug...DR8ES-L...gold...DR8EVX...iridium...DR8EIX

CB750-K7...standard...D8EA...gold...D8EVX...iridium...DR8EIX

CB750-F2...standard...D8EA...gold...D8EVX...iridium...DR8EIX

DR8ES-L stock number...2923
D8EA s/n...2120
D8EVX s/n...2850
DR8EVX s/n...6354
DR8EIX s/n 6681