SOHC.co.uk Forums > CB500/550
Plugs fouling at idle
deltarider:
--- Quote from: K2-K6 on April 25, 2024, 10:53:58 AM ---[...]
Another observation, the Boyer ignition is very, very competent in it's delivery. I've no problem working with the std system, believing it to be mechanically almost peerless in it's design, application and component specification .... the Boyer i can see by comparison does offer tangible benefits if that's chosen by the owner though.
Among those benefit appears the ability to fire more adverse mixture range more of the time with exceptional repeatability. This seems to support a more optimum idle mixture that may give benefit in any residual unburnt component/fuel that may be affecting the fouling determination this topic is about.
[...]
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The advantage you attribute to B#B, is valid for any EI that has a transitor doing the switching. Realise that even in stock configuration, coils will be fully saturated. Only in border situations a transistor has the advantage of more reserve as there's no loss due to mechanical breakers (tiny sparks can be seen in stock set up). The steeper rise time a transistor ignition provides, will also offer some reserve in border situations. That's all to it, I'm afraid. There's no shortage of spark duration because @ idle initial peak voltage will be relatively low (estimation around 7kV). An EI will NOT give a higher voltage. Why should it, if the circumstances are thus, that already 7kV is enough to bridge the plug gap. Ergo: lots of energy available.
It's the gap that determines a higher or lower initial peak voltage and the atmospheric circumstances in the combustion chamber ofcourse.
In my personal situation, I'm experimenting (you guys know me ;)) by following what is advised in a American Honda booklet. Needles are now raised one notch (and thus in 4th) and the airscrews are two turns out.
Here is something I have never communicated before. In the very first year I owned my CB500 (1980), I travelled as far as Greece. On a camping in the Peloponnessus I decided to open the Haynes manual. Being completely ignorant I followed the data in forsaid manual and have set the airscrews at one turn out. To this day I wish I had never touched them. I should at least have made a note what they were in before. Immediately the next day I noticed a difference: a negative one and never thereafter in 44 years have I been able to regain that perfect utterly smoothly accelerating CB500 again. Don't take me wrong. It has always been good thereafter, but never so perfectly accelerating as before. Later the properties of gasolines changed which made it even more difficult. That's why I am always curious to know what position other CB500 owners have their airscrews in. If my plugs stay clean at idle, driveability in acceleration suffers. My understanding is that even 1/8 of a turn can make a big difference and at least one Honda mechanic has told me that the position of the airscrews of all 4 can individually differ in position more than just 1/4 of a turn. Soon I hope to use my restaurated CO gas analyzer and see what an initial 4% CO at idle will bring.
K2-K6:
You're making the assumption that I've said it needs more power (supplied by the Boyer ? ) which is not what I've stated.
I agree it doesn't, there's other attributes within that system that hold value in this performance arena.
Question .... can you describe the failure mode within the combustion chamber which gives erratic acceleration response as you've described it ? In other words, why are you not getting a perfectly linear response with the settings you have.
Honda never state (as far as I appreciate) that you have to use equal idle circuit settings, just a suggested start point, from which their setup routine .... well written in my view ..... will allow settings for individual cylinders in giving long term combustion equality. Thats just normal in my reading of their factory instructions. It goes further in the later PD carbs, such that it calls for correct settings, then to record those individual adjustment as the genuine reference point from then onwards.
Also it states that they are set in this way at factory, advises not to arbitrarily adjust them without making good record of their factory position BEFORE working on them.
Sensible, I feel.
deltarider:
--- Quote from: K2-K6 on April 25, 2024, 01:44:15 PM ---You're making the assumption that I've said it needs more power (supplied by the Boyer ? ) which is not what I've stated.
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Sorry if I did. I may have been misled by what so many believe who attribute super powers to an EI. You have shown far more knowledge. The ignition in itself is quite an ordinary process. Complicated is that we deal with 1) an idle, 2) load (acceleration) and 3) cruise.
--- Quote from: K2-K6 on April 25, 2024, 01:44:15 PM ---Question .... can you describe the failure mode within the combustion chamber which gives erratic acceleration response as you've described it ? In other words, why are you not getting a perfectly linear response with the settings you have.
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I wouldn't call it erratic. Before I touched the airscrews in 1980, acceleration was just fabulous. In my memory I was constantly turning the throttle grip forward to prevent the bike from leaping like a jaguar. Later it was just good. The mec that initially has tuned my bike - either in Japan or in Holland - must have done a perfect job. Later a Honda mec - not the same - learned me that airscrew positions may need to differ further than just the +/- 1/8 of a turn Honda prescribes. BTW, in his years long experience the CB500 was the hardest to fine tune of all the CB Fours. This could relate to the special carburetor setting, models for the European continent had. I don't know. Not much later after my trip to Greece, gasoline quality changed dramatically. I remember having read an article by a widely respected professional writer for automotive and motorcycle mags - who himself owned a CB550K3 - in which article he concluded in his last line (in despair?) that "some motorcycles just don't like some gasolines". I have never asked him, but he himself may have been struggling with his CB550K3, after the arrival of the changed gasolines.
--- Quote from: K2-K6 on April 25, 2024, 01:44:15 PM ---Honda never state (as far as I appreciate) that you have to use equal idle circuit settings, just a suggested start point, [...]
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I didn't say Honda did, but Honda did give a range of +/- 1/8 of a turn. Some mechanics judged the difference in air screw position amongst the 4 could need to be more than that. I suppose they may have had a reason for that.
davidcumbria:
Interesting thread. This fouling at idle - is this when the revs drop after running steadily for 20 seconds and can be cleared by revving the throttle to restablish the steady idle? Mine does have that tendency on the denso plugs but also one cylinder which is cooler than the others so I’m guessing that’s the one that fouls.
I have found on many different bikes cars lawnmowers-that iridium plugs give better starting, smoother idle and avoid fouling on two strokes. It seems there isn’t one available for the 550 - why not ?
K2-K6:
--- Quote from: davidcumbria on April 26, 2024, 06:28:43 AM ---Interesting thread. This fouling at idle - is this when the revs drop after running steadily for 20 seconds and can be cleared by revving the throttle to restablish the steady idle? Mine does have that tendency on the denso plugs but also one cylinder which is cooler than the others so I’m guessing that’s the one that fouls.
I have found on many different bikes cars lawnmowers-that iridium plugs give better starting, smoother idle and avoid fouling on two strokes. It seems there isn’t one available for the 550 - why not ?
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Think I'd initially swap the plug lead with it's paired one to see if the cool running transfers with that lead. If it stays where it was, then looking more at that cylinder condition, compression analysis to count that out, idle jet system to ascertain if there's any impairment.
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