SOHC.co.uk Forums > CB500/550
Plugs fouling at idle
McCabe-Thiele (Ted):
I'll put it out there, plug fouling can also be caused by oil burning.
Worn rings or valve stem seals/ guide wear.
deltarider:
It's not oil. I smell petrol so it's overrich. Fuel is different these days. Maybe Shell is right and you can adjust to leaner and save fuel when you run their V-power, which I do. The problem with these bikes is, they will always run and keep going where a twin simply quits rightaway when something is not in good order.
McCabe-Thiele (Ted):
Is it possible that you smell unburnt petrol as the oil has fouled up the plugs first - cause oil deposits on the plugs leading to unburnt petrol afterwards. Often you can see no blue smoke in oil burners.
Where rings have been replaced rather than a rebore with some glaze breaking I suspect some running in might be needed before worring about plug colours.
As an aside my 400 that was rebored by Graham has only covered some 230 odd miles - unless it starts misfiring I will not check the plug colours until it has covered about 600 miles. My idle speed is good and even - to date only bench synched the carbs as it's now running so well after my initial mistake on the plug connections when it was a two cylinder bike for a while!
deltarider:
For me the question is formost: can I indeed compensate the needles clip in 4th groove by adjusting the air screws to two turns out, like that American Honda specifications booklet suggests or should i return to the European set up with needles clip in 3rd? I have always had my doubts about that US booklet and I therefore volonteered to experiment.
davidcumbria:
--- Quote from: K2-K6 on April 26, 2024, 09:42:10 AM ---If there's response by swapping the leads over (within one oil pack) then analysis of why that could happen may give answer.
There's specific performance in the condenser relating to this (if the original system is in place) with it's ability to fire the mixture.
The opposite ends of the coil have slightly different spark characteristics, with also the condition in cylinder from the live one to the wasted spark one maybe causing a bias to disadvantage the live cylinder on compression and give a shift in performance to that cylinder.
Swapping the leads checks for that, also the insulation of the HT too.
--- End quote ---
Thanks. the leads on my bike are very stiff. I’ve remade the cap connections but I’m not very happy with them. Definitely thinking of doing the Ash fix. On the other hand it starts well and has no high Rev mis fires which makes me think ignition is ok. I can live with the slight tendency to idle foul and my air screws are out more than 1.5 turns from memory running on shell e5. I’ve improved no 1 cylinder running cool by installing #35 pilot jet and overall the bike runs very well.
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