SOHC.co.uk Forums > CB500/550
Carb jet size
Sesman:
Basically, lower air pressure requires smaller jets, but power will inevitably be reduced. Eg the air pressure at 4000ft is approximately 85% of sea level pressure. Your ‘starting point’ for a suitable jet size would be one with 15% less orifice area than standard. There are other factors such as temperature and induction dynamics (Fluid mechanics) that will influence the end result.
Regarding the original post. My 1977 550 with slightly modified inlet ports (general cleaning up and intake matching) with a dekelvic 4:1 and standard air box is using 98/38 and runs like a good un. Edit…my carbs are 069A variant.
Seabeowner:
What are the carbs. You can see the stamped mark on no 3 flange sloping side. Should be 022A I think.
Murf:
Thanks for all the replies, the atmospheric pressure and big hill were just a humorous dig at the mechanical knowledge and ability of POs, the odd jets fit perfectly with the other bodges and crap that have been done to this bike. Just my sense of humour as I am past the point of being shocked.
Anyway it did start a good discussion on altitude, and carb jetting for altitude .
But what I really wanted was info on jet size for standard conditions 😄😄.
Seabeowner, Carbs are stamped 022A .
McCabe-Thiele (Ted):
Have you looked at the table on my previous post, the table shows the jets & air screw turns.
Also depends on the model of your bike UK, USA as they were different iirc due to air cleaner systems fitted.
550 K1 should have 022A carbs see the table that shows 100 main jet, 38 slow jet.
Bryanj:
Jf you download the 550 parts book from Ashs stash it is for the us 550k models and will tell you what is standard, if its not there i can look at my paper copy next week.
Also available is a dvd with Honda manuals and parts books from me for not much plus postage
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