Topic: CB550 Air Flow, jetting, exhaust questions

[redbaron]

Hey guys, 1976 550K. My bike is together and running but not so good.  I have standard airbox, stock carbs, with a short carpy open exhaust.  I like the loud!...but, seems to be gasping for air/gas.  Any recommendations?  Would pods work better? Put a shorty muff on it for back pressure? What about carb needles? Right now they are stock.  Would it help to change to a diff size needle? what size? can I replace needles with carb bank still on bike?

[firebane]

Have you checked the floats? Ensured you have no leaks anywhere? Basic maintenance done?

What makes you think it's gasping for air?

[redbaron]

It is very sluggish on throttle and not idling good.  I will be adjusting valves and sync carbs first.  Based on other posts, a no muff exhaust can effect performance. 

[flybox1]

Stock carbs and intake plus aftermarket exhaust does not equal stock jets.
You are lean due to the lack of back pressure.  What brand are your jets?  What is your Idle mixture screw setting?
Assuming all other maintenance items are done and done correctly:
Start with your idle circuit.
Get the bike hot, put in a NEW set of D7EA plugs, and let it idle with a box fan on the engine for 4-5 minutes.   No blipping of the throttle.
Pull the plugs out, line them up 1-2-3-4 and snap a closeup picture of their insulator tips.  We need to see the color/deposits.
Post the picture here.

[BomberMann650]

I'd go for that exhaust silencer too.  One less reason for a cop to ticket you 

[redbaron]

Hey Flybox1, to answer your questions 1-the jets are stock, 2-idle mixture screw setting unknown.  I will 1-adjust valves, 2-sync carbs, 3-install new plugs, 4-start with idle circuit as you describe. It will be this weekend and I will update with outcome, What jets/needles do you recommend?  Thanks 

[Scott S]

 I ran a Carpy exhaust with stock air box and stock jets/carb settings and it ran fine.  BUT... it appears that you've cut off part of the pipe? No baffle?
 That's your problem.  You need some back pressure. Nobody here is gonna have an exact jetting recommendation for that exact combo. You'll have to do plug chops and experiment. Or, get an exhaust with a baffle.

 There still seems to be a lot of unknowns about the engine and carbs, though. You need to confirm clip position on needle, mixture screw settings, and do the 3K mile tune up and adjust the valves and confirm timing is correct. Then sync the carbs. Only then should you start monkeying about with carb settings and jets.

[flybox1]

Hey Flybox1, to answer your questions 1-the jets are stock, 2-idle mixture screw setting unknown.  I will 1-adjust valves, 2-sync carbs, 3-install new plugs, 4-start with idle circuit as you describe. It will be this weekend and I will update with outcome, What jets/needles do you recommend?  Thanks

Cant determine jets until all else is done/known.

[redbaron]

Got it.  I will add a shorty muff for sound reduction and back pressure.  I will let you know the results. Thanks again for the feedback.

[Lostboy Steve]

I ran straight pipes with a stock air box and uninfilter with 98 mains and it was wonderful.


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[gwallis]

They sell baffles that will fit in the end of the Carpy exhaust.  I bought one from China (took two weeks to get here) that has a flat blank 'but end', with holes in the throat and that flares out to 2.5 inches.

Should be enough to provide adequate back pressure.

You could also buy a wrapped baffle from J&P Cycles and make your own muffler out of exhaust pipe from Auto Zone.  I did this to my CB550F with a Delkevic Header.  See YouTube video: