CB550 - full trottle performance

[Erny]

Ah ha
"Issue is present in wide range of RPMs, I confim it from ~3500 revs ->
Simply, when at whatever revs I'll open trottle fully, I feel engine does not accelate as good as if I close trottle a bit (approx 1/8-1/4)."

That makes it a different problem to initially described,  in as much as it looks like it could take a one size up main jet if it's right across the rev range from about 3,500 upward, and worthwhile trying that first given this information and the plug colours.

You may find that if a jet change was too far,  then in future you could either check with the larger jet plus needle drop, or it would persuade you to use original main jet plus lifted needles as they would be slightly different solutions.

At least you could assess it now with less work if you have any main jets to try just one size larger.

I'm trying to get bigger jets from friend (racing with CB550), but seems he has just 120 that sounds too much
Would you have some advice where to source bigger jets (proven source) in Europe?

One point to consider:
- my setup now is : Keihin pilot jets #38, Keihin MJ #100, Keihin needles (not sure 100%) but Keyster emulsification tubes (that looks from outside excatly the same as Keihin, but cannot confim ID as I have no mean to measure it properly)
Reason for replacing tubes was due to internal pitting/corrosion of original

tubes.
Just thinking - maybe Keyster tubes have bit smaller ID holes making mix leaner compare to stock? Was lazy to replace needles too, maybe mistake

To complete story - I got this carb set as refurbished from Gerben (NL), visually looks great, but I already found that emul. tubes were quite corroded inside, making mix too rich and impossible to tune carbs properly (I discussed this already here some time ago). Now, too lean but finally equal for all cyls.

Maybe, better would be now first to check orig. needles I have installed with Keyster if there is any difference in needles thickness (Keihin for 022A shall be 2.515mm). If keyster is less, that can explain lean mix. Will try to measure soon.

Other, but quite expensive option is to find NOS Honda needle kits. Maybe someone has some to sell? 

I attach photos of 022A Keihin tube I got in refurbed carbs - 022A tube it is one on the right side of picture with 2 tubes - you can see even what was level of corrosion/pitting before cleaning

[deltarider]

When your 022A carbs are stock, there's only one notch left to raise the needles...
My gut feeling is somehow air intake is not correct. Also realise today's gas is not the same as in the 70s: with ethanol you can expect a leaner running. Like K2-K6 suggests, you could try a bigger MJ. But me personally, I'd first try - strange as it may sound - with the airscrews turned in half a turn.

[K2-K6]

The Keihin emulsion tube (rhs) has all equal holes, looks like the chart specification is 0.9mm whereas the left tube has the top two pair of holes smaller.

Doesn't look like they match the original.

120 MJ is a big jump and too far.  Others on here are more familiar with supply of jets so may join to advise.

[Erny]

to avoid misunderstanding - tubes on pic are both keihin, left one is from 069A carbs right one from 022A carbs, both are used, coming from carbs refurbed by Gerben.

Keyster (new) tube is NOT on the picture (forgot to take comparison photo), but it looks EXACTLY as 022A, so all holes equal, OD, and other dimensions are the same.

I edited previous post - put text comment into pic to avoid confusion

[Laverda Dave]

When your 022A carbs are stock, there's only one notch left to raise the needles...
My gut feeling is somehow air intake is not correct. Also realise today's gas is not the same as in the 70s: with ethanol you can expect a leaner running. Like K2-K6 suggests, you could try a bigger MJ. But me personally, I'd first try - strange as it may sound - with the airscrews turned in half a turn.

That's a very good observation. Maybe try a thankful of super unleaded first and see how it performs. Less hassle than fiddling around with jets, tubes and needles. Personally I use Shell V-Power in the Jota, anything else and it feels flat and pinks if given full throttle quickly.

[Erny]

With regars to fuel - I only use premium fuels to my bikes where possible, usually 100 octan, with 5% of ethanol max (E5). Standard fules here have 10% (E10)

I still suspect too lean issue might come from tubes being too small ID (Keyster). Need to check that before hassling with MJ and/or needles

[deltarider]

I don't know where your airscrews are set now, but I'd give it a try with them. Honda specifies 1¹/₂ ± ³/₈. I can almost predict how theorists will react, but let me put it this way: my CB500 never understood that theory. It's done and undone within a minute. Could be the easiest fix.   

[K2-K6]

Octane in absolute terms is associated primarily with compression ratio and wouldn't change the mixture.  It's mixed in with the causes of "pinking" with lean mixtures but the two reasons (too low octane induced, overheat conditions) need to be considered separately.

The overall experience from plugs and riding description are saying too lean, although not by much, which need to be addressed to bring it into more normal combustion performance.

The idle jets won't affect the upper ranges of rpm from adjustment of the air screw, but only if you changed their size. Once the idle jet reaches maximum flow it can't contribute more however the screw is set. The adjustment alters the slope of gain for idle jet flow and not the maximum. 
Air screw further out will bring maximum flow at higher speed,  in comparison to turned inwards when the idle circuit will reach maximum flow at lower rpm.

Worthwhile for some contingency protection while running is to raise the plug number by one to mitigate against plug tips going over temperature potentially causing pre-ignition,  which you really don't want.

[Laverda Dave]

Octane in absolute terms is associated primarily with compression ratio and wouldn't change the mixture.  It's mixed in with the causes of "pinking" with lean mixtures but the two reasons (too low octane induced, overheat conditions) need to be considered separately.

The overall experience from plugs and riding description are saying too lean, although not by much, which need to be addressed to bring it into more normal combustion performance.

The idle jets won't affect the upper ranges of rpm from adjustment of the air screw, but only if you changed their size. Once the idle jet reaches maximum flow it can't contribute more however the screw is set. The adjustment alters the slope of gain for idle jet flow and not the maximum. 
Air screw further out will bring maximum flow at higher speed,  in comparison to turned inwards when the idle circuit will reach maximum flow at lower rpm.

Worthwhile for some contingency protection while running is to raise the plug number by one to mitigate against plug tips going over temperature potentially causing pre-ignition,  which you really don't want.

Thank Nigel. I have just learnt something new. Everyday is a school day

[Erny]

Just measured Keyster needle (declared for carbs 022A) - it has 2.520mm that somehow corresponds to original Keyster 2.515mm.
Replacing them will (to me) make mix even more lean.

[K2-K6]

Unsure I understand which way you are saying that,  but lower number in diameter will give richer mixture as it blocks less of the main jet hole.

That for the needle itself.

[Erny]

Exactly this is what I'm saying (sorry for not being clear).

According to Gerben (who did rebuild) now I shall have in carbs genuine Keihin needle (shall have 2.515mm according to HSM or bit less as it can be worn to some extend) in combination with new Keyster tubes.

Keyster needles I have available have 2.520mm so installing them into carbs will make mix even leaner.

[K2-K6]

Yes I see which way round you've described it, and agree with you about the change it would make.

Possibly worth describing the problem as I understand it;- it's running almost perfectly as regards mixture for steady state (not accelerating) combustion.
With slide type carburettor this "perfect" mixture is reluctant to increase speed due to characteristic within the system in that as you start to open the throttle the immediate change is to reduce the vacuum in the carb throat, and force the mixture to move toward lean just at that point. This prevents the engine from gaining speed in this circumstance ordinarily. 
The way this is compensated for is the manufacturer sets the mixture effectively too rich for technically ideal running to make sure it can cover this inherent error. It's one of their limitations on a road engine as it will always have to run richer than perfect to make sure you can easily accelerate it. We also get used to seeing plug colours that are effectively showing slightly rich and accepting those as normal, but they really show the error we have to run to describe them fully accurately.

It's this that CV type carbs and accelerator pump equipped slide carbs are designed to eliminate.

Back to this engine and carbs though, and you can judge where it is mixture wise from your riding description. As you open the throttle fully it makes it too lean to gain rpm but backing off a little just brings the vacuum and so the mixture back into competent range to get the increase.
You can see from this that it's running with just enough excess fuel to cover light to medium acceleration, but not fully wide open.
What it needs is just that final extra percentage to completely cover all throttle application. 

It's very close but with that obvios error. Decision is how you make that final adjustment to get it just right.

[Erny]

Update on this topic, finally jets arrived, I replaced stock 100 by aftermarket 115 (in reality they seems to have size around 133-114). Full trottle acceleration improved. Bike runs smooth on low RPM, I can easily cruise around 2500-3000. (of course battery is no charged wirh headlight on)

Checked plugs for color, it looks to me still lean, especially plug no1 (plugs on the picture are sorted from left). Wondering if I should go one step more wirh jets (120?) or let it be.
Using Shell V-power racing petrol, as this one still has "just" 5% of bioshit (E5). Others are E10 here. Maybe plugs color can be explained also by petrol used?

[fogrider]

Looking at those plugs , my opinion is you're pretty close with mixture and ignition timing. The plug colours are deceptive because, it seems to me, that your engine is burning a bit of oil. I've also seen plugs get that sort of sheen when someone was using a high detergent diesel engine oil.

Watch your oil level !