SOHC.co.uk Forums > CB350/400
400/4 is popping & banging with poor mpg where to start?
bruxby-clive:
Hi Ted, where did you get your plugs from? I had an intermittent fault on my KH 250 which I finally traced down to a sparkplug breaking down, my fault as I bought them off eBay, as soon as I replaced the plug normal service was restored. Although I do appreciate that as it is with 2 cylinders it is unlikely but worth a check.
McCabe-Thiele (Ted):
--- Quote from: TrickyMicky on June 17, 2022, 08:25:57 AM ---Enjoy the aqueduct, Ted. It's quite an 'interesting' perspective if you admire the view from the West facing side, (not the towpath side!). Mike.
--- End quote ---
I guess you mean the sheer drop looking over the side of the tank sections - yes looking forwards to it.
I did visit briefly once since 1968 with a fellow student only to find the hand rails were missing on the tow path side - it was a windy day so what started as a walk ended up with me crawling a short distance before common sense prevailed and I turned back.
McCabe-Thiele (Ted):
--- Quote from: bruxby-clive on June 17, 2022, 08:47:29 AM ---Hi Ted, where did you get your plugs from? I had an intermittent fault on my KH 250 which I finally traced down to a sparkplug breaking down, my fault as I bought them off eBay, as soon as I replaced the plug normal service was restored. Although I do appreciate that as it is with 2 cylinders it is unlikely but worth a check.
--- End quote ---
The plugs were purchased from e-bay via UK seller that had good feedback - I have a new set from DS in reserve.
McCabe-Thiele (Ted):
Mini update I have removed Plug 1 photo below it was clean but wet with fuel.
Plug 2 looked pretty normal - slightly on the rich side perhaps.
I'm confused as all 4 manifolds show heat discolouration as 1 & 3 have a cold front pipe find it hard to believe it would run on just 2 good cylinders.
Plug No 1 by Macabe Thiele, on Flickr
Number 2 below.
Plug No 2 by Macabe Thiele, on Flickr
Numbers 3 & 4 will have to wait until next week as I need to do some tasks round the house first.
K2-K6:
#1 definitely wet with not enough spark-age or too much fuel-age, question is which one? #2 looks fine for combusting (slightly in shadow to see exact colour) but clearly dry and carbon as expected from continuously running cylinder.
Could be as Ken says, a sticking float valve that is giving it a bit of a soaking.
The #1 plug, just try it for sparks in another system to see shat it does (independent ignition scource) that will point you to what's happening and give you clear answer if plug will spark at least.
Enjoy the aqueduct trip Ted, often seen it on TV but not visited and looks pretty spectacular to cross it.
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