Where did my thread go?

[Oddjob]

Seems pretty self explanatory to me Bryan, of course we’ll get the answer it’s not the same type of carbs etc. You can lead a horse to water but you can’t make it drink.

[K2-K6]

Thanks Bryan, that's very clear to me.

In regard to carburettor type and relevance, this is not conditional to that but to the combustion characteristics of current fuel and the engine being worked on.

In very simple terms (it's using the hardware in place as method of measuring combustion air fuel ratio) uses known combustion effects of A/F ratio to determine complete mix point of burn THEN adds more fuel to that setting to bring down rpm by making the ratio richer. This the same for any carburettor that has a idle control circuit separated from main venturi in providing for accurate low level fueling demand.

That's all it does, nothing else. Its not responsible for part throttle opening response, nor any other characteristics. They have their own means of adjustment.

More involved detail, this is specifically to separate and set the off load /closed throttle air fuel ratio and NOT the initial opening part (under torque loading)  of throttle mixture, which is controlled by the idle jet size.

[Bryanj]

I just knew i had read it in a Honda manual and luckily tripped over the 750KDOHC one whilst looking for some thing else, as usual!

[K2-K6]

I just knew i had read it in a Honda manual and luckily tripped over the 750KDOHC one whilst looking for some thing else, as usual!

It's interesting the point you made to me recently, that when these bikes were used in 1970s etc, they were and didn't need any real adjustment to this part, they just worked.

I agree with that as constant use, no ethanol, no sitting around for weeks/months etc, nothing changes and they work very well.

Many threads in this are on here are now because in part, or all of the above, along with stripping, clearing, worn components etc, that now needs untangling in chasing a fault in running response on these bikes. Many of these situations simply going further than original manuals could ever envision, making identification of real fault quite involved.

One area I can see, and learnt from forum contribution, is from Skoti in longer term with clear evidence of worn components in main jet and needle. This recently backed up by exvalvsetdabbler and his in depth assessment of this very aspect in his carburettor hardware during rebuild. Quantified assessment of this type are valuable to forum information, particularly in respect to understand whats happened to older components.

The function of that particular area, and seeming to show most wear too, is to all but close main jet flow at low throttle slide position, that in  handing over metering to the low speed circuit. With wear there to compromise that function, it'll be all but impossible to set idle circuit accurately as in effect it has supply of un-metered fuel that distorts the fine resolution metering needed to run at that low level rpm.

Undoubtedly, the original manuals easily facilitated setup when these were ex factory bikes. They are not even complicated to adjust and set.

Given the conditions under which many currently operate though, then the manual can't really go deep enough into the topic to reveal much below that level.

[Bryanj]

Very trus, in all the years i have been doing this i have only ever seen one VISIBLY worn needle and that was on a grey inport Suziki twin of about 400cc from memory and that was ridiculously worn to the point of nearly falling in half, about 1/3 down from top.
Same as in all the 500 i have done i oly ever found one worn crank and again that was so worn it didnt need a mic to say it was scrap!

[K2-K6]

There's very good advice in those Honda manuals, but takes some additional understanding to fully appreciate certain aspects of the written words.

I refer to them so others can appreciate what was explained by the manufacturer when they made them, specifically to not claim them as my own thoughts, but give full credit to their understanding and foresight when they were published. 

That information was though never intended to go as far as I feel we can delve into them now.

My understanding now, and this changes as variously problems bring up different error and force me into reappraisal of my own experience.

I noted on the deleted thread that 3 key parts exist in how the idle circuit is made to meter fuel for different load scenarios.

#1 The idle jet size. This gives the total/maximum flow of fuel the  circuit is capable of delivering. That is set for peak demand under acceleration load, too little here will flat spot (too lean) before the carburettor moves onto main and needle metering.
#2 The aiscrew and it's position when set through adjustment. This is SOLELY there to give reduction of the potential fuel delivery from #1 above. Specifically, to set the exact air fuel ratio at closed throttle position,  that to give a co reading of 1.0% which should equal 14.2:1 air fuel ratio in combustion.  It has absolutely no load on the motor, only internal friction , heat losses, alternator etc.
More over, it holds the key to stable idle which these were originally renowned for.
It has no function in compensation for any other aspect.

Between these two, running concurrent/concentric whatever way you want to describe it,  they can be set completely separately by change of jet and adjustment of screw. This is vital to understand in how to specify them.

#3 This is the "hidden" function that links the two above (you'll have to go a long way to find description in general working instructions) but gives the translation from idle mixture flow in "ramping" up delivery to ultimate flow of idle jet size in response to throttle slide being opened.  In effect, the sizing of the components along with entry and exit ports, gives a airfuel proportioning function, and that without moving parts.

Overall it allows separately the setting of peak, floor and transition rate of this circuit by understanding how to set them and knowing which part of rpm response is giving a problem in running conditions.

The really clever part of Honda's instruction is that by moving the airscrew it will show you if there's response and by the range the screw us moved, it tell you tge existence of faults by that "measurement" if you know what to look for.
If it doesn't change anything, that would indicate more fundamental fault ultimately to direct the attention toward finding what is wrong to cause that failure.

In essence, this is like an engine check light on a modern vehicle. If that screw shows out of range when trying to get response, it shows the low speed metering or something else (ignition? or leaking intake) is present.

[K2-K6]

With the above detail and understanding, we can use this in a real case to test the data in finding out whether there was false analysis.

Our Dutch co-respondent wrote the technical details of how he made his projection in regard to this topic.

Stating that his bike would not respond correctly in the phase that starts to open the throttle, usually meaning a flatspot from lean running.

He identified, in his solus example, that the airscrew needed to be turned inward during closed throttle idle in eventually bringing the co value from typical of 1% up to the range of 3 ~4% from my recall. This to give correct response to opening the throttle.

If we look at this from the Honda's manual perspective and setting routine, it shows us that the engine needs more fuelling as throttle opens, this is correct. But the method of achieving this he's used is wrong.

What should happen is to give the extra fuel needed by changing the size of the idle jet to a size larger. Then reset the airscrew to give the correct idle mixture metering with throttle closed.

The "fault" he's installed through his action is that he's accepted the error in total peak flow of the idle jet, and then incorrectly used the screw to compensate, which is not its task.
The result is now TWO mixture errors. Too low peak idle jet flow, too high off throttle mixture enrichment. 

What this does is run excessive fuel through the combustion chamber (co target of 3-4% gives something in tbe oder of 12.8~13.1:1 A/F ratio) which is not needed off load, furthermore it's not burnt. This excessive fuelling will go toward washing lubrication from cylinder bore and help in promoting internal  exhaust corrosion effects. It's effectively running it on partial choke continuously.

Changing the size of idle jet first will give the low throttle opening response, along with the higher end of the initial phase leading up to the main jet supply coming on stream.
Airscrew can now set, correctly, the closed throttle mixture, independently, to it's optimum point. There's no need to compromise.

There's further effect too. Notably he's put on forum before about not being able to get a stable low rpm idle with the setup he used. Thats no surprise as running around 12.9:1 ratio at idle will always need more throttle opening to keep some semblance of equilibrium on what is essentially part choked running condition. This resulting in elevated idle rpm.

He doesn't need a video (as demanded) to demonstrate the Honda method, his own evidence in data and setup given on this forum is absolutely proof his assessment is wrong.

That's why his stance should not be taken by us as any way to set up these carburettor for the forum.

I did suggest he came with more conciliatory outlook in tbe deleted thread, that was clearly refused. We could have discussed this at more length to appreciate properly how this system is designed and works, before now.

But he chose to " sanitize" us, the great unwashed on here. He clearly hasn't understood which part of the equipment relates to which problem is experienced.

[deltarider]

With the above detail and understanding, we can use this in a real case to test the data in finding out whether there was false analysis.

Our Dutch co-respondent wrote the technical details of how he made his projection in regard to this topic.

Stating that his bike would not respond correctly in the phase that starts to open the throttle, usually meaning a flatspot from lean running.

He identified, in his solus example, that the airscrew needed to be turned inward during closed throttle idle in eventually bringing the co value from typical of 1% up to the range of 3 ~4% from my recall. This to give correct response to opening the throttle.

If we look at this from the Honda's manual perspective and setting routine, it shows us that the engine needs more fuelling as throttle opens, this is correct. But the method of achieving this he's used is wrong.

What should happen is to give the extra fuel needed by changing the size of the idle jet to a size larger. Then reset the airscrew to give the correct idle mixture metering with throttle closed.

The "fault" he's installed through his action is that he's accepted the error in total peak flow of the idle jet, and then incorrectly used the screw to compensate, which is not its task.
The result is now TWO mixture errors. Too low peak idle jet flow, too high off throttle mixture enrichment. 

What this does is run excessive fuel through the combustion chamber (co target of 3-4% gives something in tbe oder of 12.8~13.1:1 A/F ratio) which is not needed off load, furthermore it's not burnt. This excessive fuelling will go toward washing lubrication from cylinder bore and help in promoting internal  exhaust corrosion effects. It's effectively running it on partial choke continuously.

Changing the size of idle jet first will give the low throttle opening response, along with the higher end of the initial phase leading up to the main jet supply coming on stream.
Airscrew can now set, correctly, the closed throttle mixture, independently, to it's optimum point. There's no need to compromise.

There's further effect too. Notably he's put on forum before about not being able to get a stable low rpm idle with the setup he used. Thats no surprise as running around 12.9:1 ratio at idle will always need more throttle opening to keep some semblance of equilibrium on what is essentially part choked running condition. This resulting in elevated idle rpm.

He doesn't need a video (as demanded) to demonstrate the Honda method, his own evidence in data and setup given on this forum is absolutely proof his assessment is wrong.

That's why his stance should not be taken by us as any way to set up these carburettor for the forum.

I did suggest he came with more conciliatory outlook in tbe deleted thread, that was clearly refused. We could have discussed this at more length to appreciate properly how this system is designed and works, before now.

But he chose to " sanitize" us, the great unwashed on here. He clearly hasn't understood which part of the equipment relates to which problem is experienced.

Answer me this. How in the world can I after my succesful readjustment, have arrived at an improved mileage? Before at best 18km to a liter, now 20!
This is often what experts that work with Dyno banks have seen when they have freed bikes from all too strict rules on emissions. They run better and more economical. BTW 4 - 4,5 % CO at idle was not uncommon for that era. Do me a favor. Try to have a CB500 run with 1% CO at idle. Don't make me laugh.

[SteveD CB500K0]

This thread is heading the same way.


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[Bryanj]

Steve, is it possible for a member to block and not see a contributers posts? Somehow i doubt it but it would be nice

[Sesman]

Who knew that 4 screws could attract so much ‘discussion’. 🫣🥱

[Nurse Julie]

Who knew that 4 screws could attract so much ‘discussion’. 🫣🥱

🤣🤣🤣🤣🤣🤣🤣

[Bryanj]

Depends on if they are stainless or brass and countersunk or button

[Laverda Dave]

Fuel injection is the way forward, no screws just a laptop with maps🙂

[Oddjob]

Who knew that 4 screws could attract so much ‘discussion’. 🫣🥱

My 4 screws with the wifes sister prompted much more discussion and far more heated I may add.

Just joking, her sisters ugly.😆😆