CB550 carb adjustment/tuning

[scanderson76]

Hello all,

I hope that the experts on this site will be able to help me get my 550k dialed in. I recently purchased the 78' 550 with the POD filters and MAC 4 to 1 exhaust already installed on the bike. The bike came from an elevation of 1000ft above sea level and I live at 5000ft above sea level. I knew I was going to need to do some tuning on the bike so my intention was to get a jet kit. Now I know after reading many posts on here and SOHC 4 that it is best to go with authentic Honda parts. This is my intention and I was curious where you guys go to get these hard to find little gems? Currently the bike has trouble starting up and staying idling. Should I start with adjusting my idle screws with the comments I found in the carb theory 101 section? ( I found this to be especially helpful). Any assistance would be greatly appreciated. Oh, also a little background I have a decent tech level as I used to work on large equipment (wind turbines), but my tech level with these little bikes is fairly limited. However, I sorted out the rat's nest wiring from the previous owner on my CB400f so I am not a complete mellon head!

 

[kopcicle]

adjust the valves
make the dwell and timing as identical as possible for both point sets at 3k rpm or better
timing at idle is less important .
sync the carbs at idle and 3k rpm . split the difference if they are drastically different or look to linkage problems .
only then do you mess with the idle mixture . If you don't know or have never heard the term "lean idle roll off" then you have a bit of reading to do . It's not uncommon for idle mixture screws to vary as much as 2 turns from one to another when correct . Comments like "I adjusted all my idle screws to 3 turns out and still can't get it to idle cleanly " are daft and downright ignorant .
If at first you don't succeed try a different idle speed setting . if set too low primary baclash will catch you out . if set too high return to idle will lag . If results are inconsistent look for vacuum leaks . If a mixture screw fails to react clean and physically examine the entire idle circuit and try again .

as a last resort for a worn engine increase the valve clearances slightly ( like a half thousandth ) and try again . if it improves you need valve work .

If you decrease spark plug gap and it improves check for full battery voltage at the coils as well as excessive resistance at the spark plug cap .

make sense so far ?

Oh and if you don't adjust the valves first all of this doesn't matter and gawd almighty will kill a kitten .

~kop

 

[scanderson76]

Thanks kopcicle! I will look into the valves first and go from there. I will report back with my findings.