Topic: Jetting 1977 CB550K

[fourguy]

I'm new here,living in belgium so my english will be spitting sometimes.The past 6 monts i've restored a 1977 CB550K...frame,engine,carbs etc.(not complete yet,tank,side panels needs to be painted).The bike came to me with 4 into 1 Marshall exhaust,witch i've cleaned up and still on it.My dream would be 4 into 4 originals (thats a dream..).Now with the marshall,engine is not running smooth,the power in low rpm's is very lazy,end no smooth ride true the gears.The problem is i think,to lean mixture with 4 into 1.My carbs type is PD46C,main jet 90,pilot 42.I now CB550F had stock 98 jets (diffrent carb to).Would it be a good idee to put 98 in my carbs.Anybody with a good jetting tip with the 4 into 1 Marshall?

[TwoTired]

What air filter are you using?   Is it clean as new?
Stock 4 into 4s that aren't rotted are getting pretty rare, here in the states.

I don't think you can compare the main jets from the F model to the K model, as the PD carbs have a different venturi shape than the earlier style carbs on the F models.

Depending on your air filter, the less restrictive pipe may need a larger main jet though.  Please note that the main jet size is selected for operation between 3/4 and wide open throttle.  Mixtures for throttle positions between 1/8 and 3/4 are dominated by the needles in the slides.

Also be aware that the pilot jets have very small orifices, prone to clogging.  Being pressed into the carb bodies, some folks are reluctant to pull them out for a proper cleaning.  Unfortunately, if the bike hasn't been in continual service, or seen routine clean fuel, they clog up.  Symptoms are poor idle and head pipes that are cold(er) than others when at idle.

Lastly, I'm quite certain your English is far better than my Dutch.

[fourguy]

Thanks for the answer,now the airbox is stock,airfilter is as good as new,carbs cleaned for several times.I will have to be honest on the pilot jets,i never took them out because i can't get them out.I've almost skimp one flat on my attempts to get one out.So i leave them in.I'm going to trey now moving the needles one mark up,see how it reacts.

[d3buttz]

Dumb question-What is the elevation in belgium is that why you went so low?  90's for your main seem to be a very low number main-that would make your bike run lean for sure.  Lower numbers are for higher elevations (and other reasons).  Here in denver i live at over 5000 feet and 98's still would make the bike run alright.  i would go back to the 98's and all stock carb settings and omit any other issiues that could be going wrong first-also look a your float heights-incorrect height wouild explain low idle power loss. good luck

[Sporkfly]

Dumb question-What is the elevation in belgium is that why you went so low?  90's for your main seem to be a very low number main-that would make your bike run lean for sure.  Lower numbers are for higher elevations (and other reasons).  Here in denver i live at over 5000 feet and 98's still would make the bike run alright.  i would go back to the 98's and all stock carb settings and omit any other issiues that could be going wrong first-also look a your float heights-incorrect height wouild explain low idle power loss. good luck

90 main jet is stock on the '77 model 550K.

That said, you say the filter is good and "like new" - does this mean that it is not new? If it's not new, replace it. The needles should be at the second clip position (not third as the earlier model carbs). I highly doubt the exhaust would cause very noticeable issues as you describe. You may not have everything cleaned up. As for the pilot jet, it would be best to get some soft jawed pliers, such as lead or similar but wrapping regular old pliers with electrical tape works in a pinch, and gently (I use this term relatively) pulling them out.

I just really doubt the exhaust alone would cause serious issues with the low end power. I would double check everything from the mixture screws to all jets and passages clear and get a new filter, not a filter that appears to be new. The fibers will break down with age even if there are few miles put on the filter.

Edit - Love that exhaust.

[Deltarider]

Would it be a good idee to put 98 in my carbs.

Yes,#98 or #100, whatever you can get your hands on.

The fibers will break down with age even if there are few miles put on the filter.

Mine don't.

[TwoTired]

Before you change jets, check the spark plug deposits.  Compare to this chart:
http://www.dansmc.com/Spark_Plugs/Spark_Plugs_catalog.html
This will give you an idea whether you are starving for fuel or have an excess fuel in the mix.

I've found that unless you have a very small inlet restrictor ahead of the filter media, the filter paper can only be cleaned so many times before it becomes the most restrictive part of the induction system.  The fibers simply compact and store dirt that can't be blown out.  For me it was about a year before it would soot up the plugs fairly quickly, despite repeated cleanings.  A new filter made the spark plugs have tan deposits again.  I eventually switched to a UNI NU-4055 foam air filter element in place of the stock paper type.  The foam element is cleanable and reusable as new, making it far cheaper in the long run.

For those offering advice about jetting, please note he has the PD style carbs, not the earlier style.  They have different jet requirements.

Further,  the low speed is quite effected by the pilot jets.  If they or the small emulsion tubes at their outlet is not clean, low speed performance will certainly suffer.
It would be nice to know if the head pipes are all at the same relative temperature.

Cheers,

[SteveD CB500F]

Thanks for your help here Lloyd. I recommended this site to fourguy who had posted on sohc.co.uk - we have nowhere near as much experience in this as you guys (plus only 10% of the audience!)

[fourguy]

O.K. Thanks,all of you guys.I'm going to make work of all the points you've say.You will hear later what it came out.At the moment it's very bad weather in belgium (rain,wind..),no good testing conditions.In the mean time going to take the carbs of (..again).