SOHC.co.uk Forums > CB750
My '71 CB750K1 is quite slow...
Nurse Julie:
It sounds like the plug type may not be helping. You are using resisted spark plugs (the R denotes that) and if you have resisted plug caps fitted, which by your avatar looks like you are, you will be getting too much resistance. Change the plugs to NGK D8EA'S or the DENSO equivalent as Dennis suggested. You only need one element resisted, either the plug caps or the plugs, not both.
Spitfire:
I'm with Julie, I made the same mistake with my bike with resisted plugs and caps.
Here's a discussion form the US site
http://forums.sohc4.net/index.php?topic=77832.msg869100#msg869100
Cheers
Dennis
PaulS:
Thanks philward, yes, standard (original) intake, the gaiters and clips are in good condition, and the exhaust is standard HM340 except one replacement pipe to pattern. I'll adjust the needle to get the mix a little leaner.
In the meantime I will take the medicine offered by Nurse Julie and confirmed by spitfire - I'll replace the plugs!
Andrew-S:
--- Quote from: PaulS on August 23, 2021, 11:52:22 AM ---Thanks philward, yes, standard (original) intake, the gaiters and clips are in good condition, and the exhaust is standard HM340 except one replacement pipe to pattern. I'll adjust the needle to get the mix a little leaner.
In the meantime I will take the medicine offered by Nurse Julie and confirmed by spitfire - I'll replace the plugs!
--- End quote ---
Original K1 exhausts are HM300, the K2 was fitted with HM340 with extra baffling so maybe they are restricting the carbs/gas flow - not sure if you have to change the main jet when fitting HM340s but someone will know?
Cheers,
Andrew
PaulS:
Apologies Andrew-S; I have just checked and the pipes are HM300 (apart from one pattern replacement), all with O/E baffles.
Will let you all know how the 'tinkering' goes. I have ordered up the Denso X24ES-U plugs...
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