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400 Four detonation

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hairygit:

--- Quote from: K2-K6 on February 06, 2018, 09:36:48 AM ---Good question Drew, I was thinking about that too.

It's something that's not claimed generally by most types of system. They normally go with fatter / hotter spark, improved starting, improved high speed accuracy etc, making it difficult to see if they have considered more in depth issues and completed a design to address something very specific. They appear, in this field generally,  to cover this sort of stuff with words like "improved driveability" which could mean any number of things.

The Boyer has always seemed a very competent system but ultimately it may be worth posing a specific question to them to understand, in their view, how they approach something like this.

It's complicated by the Honda original, in my view, being a very good mechanical design with some clearly very subtle qualities that are very hard to improve without very specific knowledge.
The area that would seem in the original fit to be most influential is the length of spark,  ie duration of the spark event. Honda appear to have designed in a specific length that would benefit their combustion chamber requirements. The bigger is better school of thought may trip up on something like this.

This is pulling together what I view as happening to produce error;  with a still relatively low piston speed at around 2/4000rpm the ignition reaches its maximum advance. The time of piston travelling during the period of spark initiation until piston reaches tdc,  if it's more time than spark duration,  then the spark will have completed prior to tdc. It looks to me that Honda are trying to cover this area of interest by designing in a "long" spark.
If a replacement system shortens the spark,  it looks like this area is the most vulnerable to complications. So anyone claiming a shorter ignition duration will appear suspicious.
It's notable ( I think it's correct)  that Honda delay the max advance rpm point for the 400 Four above those of the 500 / 750 so they are also massaging this point as well to avoid the detonation as I view it. I think the Boyer doesn't change this spec but also uses it for the whole range of these four cylinder engines.
If you then add in that mixture curve that we can see has the possibility of going very lean (peaks about 15.7 parts air to fuel ratio) it all meets at this critical point,  making it very marginal to get a clean combustion event completed.

--- End quote ---
Ultimately I think the issue is down to allowing the engine to labour at high throttle openings at low RPM, these Honda's are designed to rev, the max power is developed at high revs, and restrained use of the throttle at low RPM in high gear is the answer. If you want to go faster, knock it down a gear or two and let it rev freely.

Sent from my X6pro using Tapatalk

K2-K6:
Agree,  hairy.
Being more informed about why you've got to do that and take account of how they run will avoid giving problems.

It's fairly common though, as discussed, to impose or overlay things like the British bike experience onto these bikes though,  particularly as newcomers to these generally see them all as old bikes with no real distinction or separation of their care.
I was speaking recently to a 750 K6 rider at a bike meet, really nice example. I said it sounded good and asked as to how it was running, he replied that he'd given it a bit of a thrashing on the way there "and took it right up to 5000rpm" which really is nowhere near using the full range.

That fuel trace at the beginning is run in 4th gear,  so knocked down two from top. The essence is, I suppose, that if you find yourself with dropping speed and you continue to open the throttle more with little or no increase it should alert you to back out of it or drop ratios until it does what you ask of it.

Interesting that two more, in addition to Julie's,  have turned up on here with apparently the same issue. Plus the two cylinder heads of 250 /350 engines over on another thread with very close failure type.

It certainly makes a different view of running them on pod types airfilters, and trying to jet them without a dyno facility look easy!   :o (definitely a joke :) ) if it's not understood about the original intricacies,  how can a competent decision be made? Particularly if you change the carefully set vacuum gradient that Honda sent it out with.

I suppose this thread is a bit of a walkthough and illumination of what really affects them.

Drew400:
Thank you again.

Any excuse to 'thrash it' over 5000rpm sounds good to me.

Common sense tells me to drop a cog (or two) when the power runs out... two-up, headwinds, etc. But that's true of every bike I've owned.... apart from the XS1100 that could torque it's way out of prison!

Cheers, D.

Rudi45:
Hello,
i´m new here, but I will post later on in the new member introduction.

Excuse my poor technic English.
I will show you my Dyno run,  direct after rebuilding the Motor with new piston an so on.
I hope you can read this



Drehmoment = torque
Luft, Kraftstoffverhältnis = Air-Fuel
Max. Leistung = Max power

Regards

Rudi

K2-K6:
Hello Rudi,  welcome to the forum.
Your English is fine and I think much better than German is spoken by us over here. So all ok.

Thankyou for posting your dyno run printout which is interesting as part of the subject discussed on this thread.

It'll be interesting to find out more about your engine and if you have experienced something like the original problems that initiated this thread.

Nigel.

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