SOHC.co.uk Forums > CB500/550

CB550 - full trottle performance

(1/8) > >>

Erny:
After I finished assembly of my CB550 back to life (http://www.sohc.co.uk/index.php/topic,23823.msg234963.html#msg234963) I did test of newly set carbs and observed following:
When accelerating using full trottle, bike accelerates but slower than I would expect (roar noise is increased of course), almost having feeling that opening full trottle is somehow "braking" engine revving fast. But closing trottle a bit (maybe 1/8 or 1/4) significanly increasing acceleration speed.
Based on my understanding how these carbs works, in such full trottle opening only main jet is in chanrge of A/F ratio, thus logically I would assume mixture is lean so I should replace main jets by bigger ones? I did not do plug test (yet) waiting for good weather occation...

Current bike and carb setup:
- bike is practically 100% stock, air filter element is aftermarket from cmsnl, replaced as new 2 years ago (up to 3.5k miles on it)
- carbs are 022A type, 38/100 jets, genuine Keihin.
- carbs are clean, setup according to HSM, otherwise than high spped (full trottle) running very smooth

Strange is that I did not observe this behaviour, maybe I just did not realise or this is "new" issue.

Any ideas?
If conclusion is to test bigger jets, how big then? 105? 110?

Note: normally I would expect changing main jets on otherwise stock setup will not bring any improvement and all works as it shoud

Bryanj:
Full throttle at what revs?

Erny:
Approx 7k and more

K2-K6:
Showing just a little lean (vacuum is down slightly when throttle is wide but revs not yet high enough) should clean up if you lift needles to bring in main jet earlier.

You could try two notches to see what you get as if it cleans up all ok. If there's still some effect then it would suggest one jet size larger.

K2-K6:
With the above,  you may also have to fine tune the idle mixture a very small amount to make it leaner if it feels too rich in low to mid range. Emphasis on very small, just to move and refine it.

Navigation

[0] Message Index

[#] Next page