SOHC.co.uk Forums > CB500/550
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:
--- Quote from: AshimotoK0 on February 25, 2022, 08:30:24 PM ---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)
--- End quote ---
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:
--- Quote from: Sesman on February 25, 2022, 08:27:49 AM ---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…
--- End quote ---
Just wondering why I see my nick here :o :D
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