CB500 runs lean and doesn't want to pull through

[AshimotoK0]

Does anyone know if the springs change their rate with use when they  get 'slack' on the auto advance? I have loads  of used auto-advancers for various bikes and a few NOS ones including the 500/4, CB450 K0 bomber and CB250/350K.

I just built a test rig for where I work, which uses a linear stepper motor, load and displacement transducers inputted into an Agilent VEE  based PC XY plotter,  primarily to test the force/displacement characteristics  of the solenoid coils we use....... but it will be ideal for measuring the spring rates of small tension or compression springs (Max force is about 20kgs)

[Oddjob]

According to Mark Ash the springs get "annealed" by the constant hot/cold cycle and as they get older he recommends doing one spring at first and then the other as the bike ages. However at the age of our bikes i'd say that 40 odd years is enough to say do both.

As for being beneficial? Well it's not my theory but it is a suggestion from a mechanic with a whole wide reputation, there isn't much Mark doesn't know and he's well respected by everyone. As for Honda, in the age when the 500 was produced there was no competition except 2 strokes and those are not exactly equal. Honda did what Honda did due to economic pressures, it was designed for multiple markets so it was a compromise for varying air density etc
The theory seems to be to make the engine slower to advance, new springs aren't going to do this as they will just act as Honda designed them.

Here's a extract from Marks replies "most likely because the design suffers from a too-soon spark advance that causes the engine to spit back toward the carbs until about 2500-3000-ish RPM, which then makes the carbs run slower and richer than they should at that RPM"

I got a lot of suggestions for improving BHP, improving response and making the engine better for round town along with some stuff for track. I suppose all these will be in the new book. As the 750 book is regarded as a sort of bible I'd imagine the 500 will be regarded in the same light.

Phil, I'll be doing the mod BUT I'll also be doing quite a few other engine mods, like the camshaft one we talked about, matching the inlet manifolds, porting the head etc.

[Sesman]

Should be a sweet motor, Ken. Would be interesting to do a dyno contrast and compare exercise with an unmodified 500 in decent nick?

[K2-K6]

Does anyone know if the springs change their rate with use when they  get 'slack' on the auto advance? I have loads  of used auto-advancers for various bikes and a few NOS ones including the 500/4, CB450 K0 bomber and CB250/350K.

I just built a test rig for where I work, which uses a linear stepper motor, load and displacement transducers inputted into an Agilent VEE  based PC XY plotter,  primarily to test the force/displacement characteristics  of the solenoid coils we use....... but it will be ideal for measuring the spring rates of small tension or compression springs (Max force is about 20kgs)

They don't appear to be fully "spring"steel by cursory examination (you wouldn't be able to re-bend the ends otherwise) and look more like mild steel.
The difference is primarily in the carbon content which is used to set the steel spring by quenching (hardening) then tempering to remove brittle aspects and prevent it snapping during use.
Mild steel lays below this in alloy properties (doesn't respond to heat treatment) and therefore can show creep in extension during use (won't pull itself back to designed form) they are just made long enough, a coil spring is just a torsion bar wrapped into a neat package, that any twist is usually insignificant in angle to move the material past it's elasticity point in the extension needed.
I can't see them changing in property from heat cycles as they don't appear to be a category of material that responds to heat.

Worth testing them just through intended range to see if they are hugely variable from average. 

Not do critical in ignition performance really (honda do know what they are doing) as the sooner the engine can take advance the more torque it can make at that rpm. They all run effectively too much mixture to make it risky in broad terms.

[Erny]

I’m a bit confused by this one and I’m watching and learning. I thought Erny began this thread stating he had a very obvious and extremely lean burn? This may have precipitated his subsequent query about appropriate air boxes/filters. Purely out of interest, would a single tooth cam timing error create this lean mixture situation?

Sounds like poor Erny will have to start a sequential diagnostic programme…..cam timing….ignition timing and advance…valve settings….fuel supply. This will then only leave the carbs and air system?

Just wondering…

Just wondering why I see my nick here   

[Erny]

If I may contribute with my story:

Back in 2019, I was working on low RPM hesitation/too rich problem with my CB550K1 / 022A carbs (engine hesitating in lower RPMs and felt like too rich)

Finaly I fixed that:
1. I first replaced points and advancer by Boyer ignition (I kept stock coils). Result - engine hesitation at lower RPMs almost gone! This for me confirms Mark's advice with worn/annealed advancer springs as Boyer has built in advance/retard in ECU. Checked with strobo, it now works as it should. But back to this topic reported too LEAN by RBoss - I think that advancer spring issue is rather too rich "effect". I discussed that with Mark Paris too BTW

2. Too rich problem was caused by corroded emulsification tubes (genuine Keihin) that had bigger ID holes due to corrosion. Replacement by new Keyster (OEM needleds kept) and later by new genuine OEM set (tube+needle) fixed that. Engine now runs smooth on idle and also very smooth from idle RPMs, it picks from ~1500-2000 RPM smoothly. Current issue is that it is too lean now  (only tubes and needles changed, jets are the same)

[K2-K6]

If I may contribute with my story:

Back in 2019, I was working on low RPM hesitation/too rich problem with my CB550K1 / 022A carbs (engine hesitating in lower RPMs and felt like too rich)

Finaly I fixed that:
1. I first replaced points and advancer by Boyer ignition (I kept stock coils). Result - engine hesitation at lower RPMs almost gone! This for me confirms Mark's advice with worn/annealed advancer springs as Boyer has built in advance/retard in ECU. Checked with strobo, it now works as it should. But back to this topic reported too LEAN by RBoss - I think that advancer spring issue is rather too rich "effect". I discussed that with Mark Paris too BTW

2. Too rich problem was caused by corroded emulsification tubes (genuine Keihin) that had bigger ID holes due to corrosion. Replacement by new Keyster (OEM needleds kept) and later by new genuine OEM set (tube+needle) fixed that. Engine now runs smooth on idle and also very smooth from idle RPMs, it picks from ~1500-2000 RPM smoothly. Current issue is that it is too lean now  (only tubes and needles changed, jets are the same)

It's an interesting input,  but I feel that crosses over too many causes in this area. The problem of too rich mixture will ordinarily be assisted by a good electronic system especially compared to one that is not certainly performing well (it's one of few areas it may hold distinct advantage) and so mask the real problem of fuel metering.

The true fix is to correct the mixture as you're finding I believe.

[Erny]

In fact, I first did ign replacement back in 2019. This fixed most (not all) of engine hestation in lower RPMs that I felt as if engine has too much advance/too rich mix. However, still rough/uneven behaviour stayed in idle to low RPMs (typically, cruising in the city, you want to open the trottle a bit from closed).
This is no totally gone by replacing corroded emul.tubes last year. Now just with bench sync (using steel balls from bearings) engine runs very smooth! before it was impossible to sync carbs properly, even with gauges

Once I fix current too lean mix I hope I'm done... But knowing myself I'll be hunting to reach at least 100mph topspeed 

corroded tubes topic here: http://www.sohc.co.uk/index.php/topic,25641.msg235103.html#msg235103

[deltarider]

I have two TEC advancers and none of them give a problem. I never understood what could be gained by cutting the springs. When under 2500 rpm a somewhat fluttering idle and near idle annoys you, you can order a fresh set of springs. In normal riding practice, when I open the throttle, revs will be over 2500 rpm in a split second anyway, the advancer weights having reached the stops. What is there to gain then, that Honda overlooked? I can imagine however, that on snap closing the throttle, there may be a slight hesitive returning to a dead on steady idle, but I don't see that as much of a problem. On the contrary, it could make driveability less nervous. Let's await the results of Andreas Milke, who has made a programmable EI. When I look at the CB500/550 engine in standard form: four 125cc lawnmower engines put on a crank sharing a very tame camshaft for breathing, I don't expect much of it. But Andreas has ofcourse another reason for his experiment as the gas in Brazil contains a lot of alcool.

[Bryanj]

Honda never supplied the springs seperate

[AshimotoK0]

Honda never supplied the springs seperate

Correct Bryan .. Yamiya do these though but I wonder what they mean by 'racing' ..pretty pricey too.

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Deltarider probably means these ..but not sure if that German  club sells outside of the EU

[K2-K6]

For the OP, worth noting that it's not very far away from correct it seems and you're not looking for a big error to bring it within range.

The comments about camshaft timing (if it's been apart before this) are extremely relevant as you'll not solve it if there's an incorrect assembly there.

In addition, when it "fails" to give increased revs,  then applying the choke a little to see if it will go further is useful in diagnosing if it's just lean mixture stopping it. Then you'd have to find the cause, but it would confirm it's mostly mixture for some reason.

[deltarider]

A member on the German forum has been making the springs for years. They're also in the shop now: https://www.cb-four.de/cgi-bin/shop/__Fliehgewichtfedern-Satz-Z%FCndkraftversteller-Honda-CB350-400F-CB500F-CB550F%2BK-CB750Four-neu__20-059-02_02.03.html
Servus

[K2-K6]

Thread here has gone multi-strand 

I read much of that which Hondaman writes and think he is an original thinker with very good knowledge.

However, I don't understand what he's saying there  ("Here's a extract from Marks replies "most likely because the design suffers from a too-soon spark advance that causes the engine to spit back toward the carbs until about 2500-3000-ish RPM, which then makes the carbs run slower and richer than they should at that RPM") as the cylinder has it's inlet valve closed before the ignition timing,  sealing off the inlet tract (it can't really work if you fire it with any valve open, can it? ) and so can't really affect the mixture as such.

In engines that use a version of the Atkinson cycle ( Toyota Prius) the inlet cam is retarded at low speed low demand to increase smooth running and efficiency as it bleeds off some compression back out the inlet to reduce effective compression. But it still doesn't interfere with the combustion being sealed from going out there during initial burn phase.

The suggestion to increase camshaft duration for inlet will affect this area of dynamic flow (it usually needs more rpm to work effectively) but no engines I I understand will fire ignition with port open.

[deltarider]

First of all, according to not only me, but also to Dave500 in Austalia, to name just one, there is no flat spot. When you accelarate hard from standstill, bike goes like a rocket. I test it every year at least once. What some experience as a flat spot, is something else. If you cruise at say 4000 rpm and then open the throttle, there isn't much in house (as the Dutch expression is). This was already signalled in roadtests back then in Holland and France and IIRC it has to do with the engine design, bore X stroke. This 'shortcoming' can't be helped, but can be adressed by shifting down one or even two gears.
Now, do you see Americans, used to HD's (bikes) and 7 litre V8 blocks (cars), do that?
Until I see proof, I maintain the whole thing is about nothing; it's a created problem. Always good if you want to sell something or establish a reputation.
Note, that, as always, my comment at least can be falsified. Please do.