Topic: Pilot jets for cb550 f2 1976 .

[Paul P.]

Hi my bike is stock just rebuilt the carbs bike runs too rich 
I know there are lots of thing's that I can do before trying to change the pilot jets
But would like to know if  I was going to do so where could I get some ?
I have 38's in at the moment  and would may be try  36's 34's

My reasoning behind this is the bike seems to run fine after about 2000 rpm .

First of all I am going to try and lift the needle up one notch to try to let some air in .
OH year I have had the air screw nearly hanging out lean's it a bit but still to rich .

Any Information would be help full . I have already printed of a sheet on carb tunning from this
site that  I am sure will be helpful .

                                                 Best Regards Paul Porter . PS  I Cant Spell either .

[TwoTired]

How do you know it is running rich?  What are the symptoms that have convinced you?  Does it run rich at all throttle positions or just at idle?

Dirty air filters can cause richness as well and faulty choke butterflies.

Did you remove the slow jets and clean all the holes? 
Did you clear the air jet and all the passageways in the carbs during rebuild?
Did you use new orings in the main jets?
Have you set your float hights properly?

Lifting the needle in the slide one notch will make the 1/8 to 3/4 throttle positions richer.

Cheers,

[Paul P.]

Hi bike runs rich because it starts OK no choke needed after the bike is warm  say after 10 miles when it idels the rpm  jump from the normal 1200 rpm up to 2000 rpm  and back and forth  Also when the plugs are pulled  out they are black and sooty
also you can smell the fuel in the air 
OH year and all four plugs are the same .

 To combat this I have rebuilt the carbs new jets  main and slow new jets come with o rings
 cleaned all the air ways . Set float heights to correct levels and sync carbs
:There is a brand new air filter .
:There are no air leaks .
:All the ekectrical system has been checked coils etc All timming checked  .
:The only improvment I have had is when the pilot air screws  are turned out this tell's me the carbs need air ?
I have new plugs and they are gaped to correct spec .
I have run bike with no exaust and the air filter out but does not make much diffrence  .

Any thought on how to fix welcome    Best Regards Paul Porter

[TwoTired]

Hi bike runs rich because it starts OK no choke needed after the bike is warm  say after 10 miles when it idels the rpm  jump from the normal 1200 rpm up to 2000 rpm  and back and forth 

You can start it cold with no choke?
The RPM increase is normal behavior.  Warm engines are more efficient at burning available fuel than cold ones.  The idle speed is adjusted for a warm engine.  And, the throttle is held partly open by the rider during warm up.

Also when the plugs are pulled  out they are black and sooty

The part of the plug to scrutinize is the center electrode insulator.  It can be significant what heat range the plugs are and if they are resistor type or not. NGK D7EA is the correct type.

OH year and all four plugs are the same .

Well at least the malady is the same for all cyls.

:The only improvment I have had is when the pilot air screws  are turned out this tell's me the carbs need air ?

Agreed.  A good indication.  Are the pistons and cam still in original configuration? Overbore?

I can't help but feel you have overlooked something during your carb rebuild.  But, you would know best about how thorough you've been.  I would scrutinize the air jet that feeds the air screw and the slow jet.  And be extra certain the float hight was correct.  Maybe even verify the float fuel level was filling to reasonable point.  The smallest slow jet I've ever seen used for the CB550 was a #38, and many use #40s. 
Could it be possible that your slide needles are worn?  Do you have the correct slide needle taper profile and clip position (2nd groove from top)?  Are your Carbs stamped 069A on each carb body mount flange?  Check out this chart for clues as to what part of the carb to adjust for mixture changes:
http://www.motorcyclecarbs.com/keihin/jetting_1_your_keihin.htm

The smallest slow jets I could find for your carbs is a #35.  Since your carb style is so old, it is left off most lists for reference.  But, if you call them and can compare dimensions.

Do a google search for "Keihin jets"
http://www.motorcyclecarbs.com/keihin/keihin_jet_list.htm
http://www.factorypro.com/products/jets.html
http://www.sudco.com/keihinjets.html

I think you are looking for this one;
N424-22-019-030  #35

Good Luck!

[Paul P.]

Hi I would like to say Thanks to Two Tired It gives me a lot to be going on with 

[TwoTired]

You're welcome.  Just let us know your progress so we can all learn what you do.
Cheers,

[hondafour?]

Maybe bad floats. My friends bike does the same thing, the floats are bad. My 550 did that too, but much worse, it had bad floats. The fiber material soaks up a little gas over time. There is not enough pressure on the needle and seat and lets in too much fuel. Hence it runs rich.

later