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CB550 - full trottle performance

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Erny:

--- Quote from: K2-K6 on May 26, 2021, 10:07:41 PM ---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.

--- End quote ---

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:

--- Quote from: deltarider on May 26, 2021, 10:50:29 PM ---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.

--- End quote ---

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.

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