SOHC.co.uk Forums > CB500/550
Plugs fouling at idle
K2-K6:
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.
deltarider:
On second thoughts... I may have exagerated a bit. Fouling happens when there has been excessive idling: too many times for extended periods of time. I have made it a habit when bike idles too long, due to traffic, to rev briefly every minute or so. When idling for >15 minutes, without revving at least once, I can not expect plugs to stay deer brown.
McCabe-Thiele (Ted):
My understanding of spark plug technology is they are designed to be self cleaning at higher revs/temperatures - obviously there is a limit to this function so if the mixture is overly rich right through the range they will soot up.
I suspect throttle blipping was something we used to do to keep the plugs from sooting up at idle to make a clean getaway.
My experience primarily with cars using carbs is that a vehicle used for mostly short journey work fitted with the manufacturers standard plugs would foul up badly needing a good run to clear the carbon deposits.
I particularly remember a disabled customer who ran an Automatic Opel Commodore 2.5 GS (1974) from his home to work a distance of less than a mile. On collecting his Opel from Ashbourne it would not exceeed 45-50 mph flat out. During the course of the journey to our service department in Burton the top speed would slowly improve until it would reach 60-65 mph. After a service the car would drive like it should for a 2.5 litre straight six.
Fitting a different plug type to cope with the short journey used mostly on auto choke was not an option as the customer would drive to Scotland a few times a year where he had family. In reality he wouid have been better driving a car with a much smaller engine.
deltarider:
Unfortunately I haven't been riding like in the past: looooong stretches >130km/h uninterupted on motorways. It was always great how well the engine responded afterwards.
Johnwebley:
Could I suggest something I do,
Take the bike for a run about 15 to 20 miles get it nice and warm
When home, keep the engine running, put on centre stand
Get your long screw driver
Now ,turn one airscrew a quarter turn out,
Check what happens, blip the throttle, OK?
If it struggles,turn to previous settings
But if its OK,do another, repeat, and check
Remember, Modern fuel is different than 50years ago,
It might like a leaner tickover
Sent from my SM-A546E using Tapatalk
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