CB550K tuning help

[Luke87]

I’m having issues with the running of my CB550 and could do with some advice.

Carbs refurbished by Gerben - new main and pilot jets and fuel cut off valves (stock sizes 38 pilot 100 main)

Boyer Bransden ignition with micro coils - new 5k plug caps

Several sets of ngk d7ea plugs

Delkevic 4-1 exhaust.

Stock air box with new filter, inlet carb rubbers and o rings.

Ignition set, carbs synced. Bike starts and idles fine.

From idle to about 1/4 it runs really rich and stutters and bogs. Runs fine from 1/4 to wide open throttle.
I’ve used a colour tune which confirms it’s running really rich in the problem area.
It keeps sooting up plugs because of this.

So far I’ve set the air screws at 2 turns out, (1/2 turn leaner) which helps a bit.

I’ve checked the float levels with a gauge and clear tube method. They were almost level with the float bowl so have lowered them by a few mm which hasn’t made any difference.

I’ve have tried running with the needles 1 position lower which helps quite a bit with the low end running but then runs lean from half throttle onwards.
Have considered keeping the needles in this position and jetting up the mains to help the lean top end running.

I’m at a bit of a loss as I’d of thought it should run fine on stock settings even with the delkevic exhaust.

Any advice would be greatly appreciated. Thanks. Luke.

[Luke87]

Just to add, it never needs choke to start.

[deltarider]

Colortune does not work with our bikes. What model CB550K is it?

[K2-K6]

It looks like you've pretty much covered it from an analysis point of view.

But it does appear to be "asking" for a reduction in pilot jet size from your description.

I'd be inclined to leave the main jet alone as it appears to be in the correct range and would not conventionally be considered to adjust the idle mixture if it's OK at mid to upper running. Desirable to leave that alone and concentrate on idle alone.

Adjusting air screws,  if you don't get where you need to be when between 1/2 turn to 3 turns out,  is suggesting the jet flow is out of the range needed.
Are the easily available idle jets in different sizes?

[paulbaker1954]

Found this a while ago

May be useful

[Luke87]

Thanks for the reply’s and sorry for the delay in replying. The bike is a CB550K2 with the non PD type carbs.

Why do you say the colourtune does not work for our bikes deltarider?

I’ve just spent a small fortune at cms for a few sizes of main and pilot jets to do some experimentation.

I’m supposed to be going on a road trip to Germany at the end of July. It’s looking unlikely at the moment!

[hairygit]

Colourtune only shows the idle mixture to be correct or not on these bikes, of no use at all once above idle.