SOHC.co.uk Forums > CB350/400
Sooty plug
Nurse Julie:
👍👍👍
K2-K6:
--- Quote from: watty51 on July 15, 2019, 09:56:25 PM ---Thanks for the quick reply Julie.
I will try adjusting all the air screws out as suggested, I thought they would have to be set all the same across the carbs
Would you suggest about 2 turns out and try from there
--- End quote ---
It's described quite well in many of the Honda manuals, how to set up the idle circuits to get operating parity of combustion and not physical equivalent screws.
In effect they are acknowledging that there can be small differences in flow from carburettor casting and jetting variables that the screws are used to normalise, effectively calibration of each circuit.
In some of their later manuals it warns against changing the factory offsets, or recording the position prior to removal if worked on. Further it describes how the factory set them to allow you a method if they've been completely stripped.
It surprises me that this method that they were using in the 1960s is essentially what modern fuel injection systems do to control mixture, tickover etc. They were so advanced in so many subtle areas that are not readily seen.
watty51:
Thanks for all the advice, and after loads of reading up on the subject took bike out for a 10 mile ride.
Before I went out I adjusted number 2 air screw out to 2 1/4 turns to try and stop the plug from sooting up and thankfully it’s a lot better (see photo).
Is this about the condition you are looking for.
The bike ran loads better, still slight hesitation at 6000 rpm but only slight.
Will be checking all of the spark plugs now, to see if I can get it bang on
Nurse Julie:
It does look a lot better. If it were my plug, I would turn the air screw out by just a tad more, somewhere between then 2¼ and 2½ and hopefully that should improve performance even nearer to perfect. I found that once I had adjusted all 4, I had to lover the idle revs down by adjusting the big idle screw. You may or may not need to do this though.
watty51:
I will turn the air screw out by a tad more as suggested. I did notice the idle tick over rose so had to turn that down a bit, but tick over was a lot smoother/ less erratic.
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