Needle position

[Ashdowner]

My CB550K3 runs a bit rich, so while I've got the carbs stripped I thought I'd check the needle jet, which should be on the middle groove. It's on 2nd from top meaning it's getting less petrol through which comes as a bit of a surprise. The jets are standard as is the exhaust, and the air-cleaner is recent - and yes I really have gone to the far end of a fart to get the float levels right. Have I missed anything? Could it be oil?

[Johnwebley]

is the ignition retarded ,or to small a plug gap ?

[Ashdowner]

Ignition is spot on. Plug gap fine.

[paulbaker1954]

I have a 500 not 550 but I have spent hours fiddling with carbs

I run with needle in middle position and like you have spent ages on float heights etc

In the end I found that that the pilot air circuits were blocked and this had a big impact on running at small to mid throttle openings causing rich running

I would strongly recommend putting the carbs through an ultrasonic cleaner and checking the pilot air circuits. It made a massive difference to my bikes performance

I did post a detailed description of the procedure but not sure how to set up a link to the post so I have pasted it in again below -- good luck with it😀😀😀





The idle circuit consists of 3 holes and the pilot jet.

hole 1 can be seen on the carb wall on the inlet side throat at 90 degrees from the top before the throttle slide, this actually joins in to the hole from the air screw by the way.

Hole 2 is a VERY small one at the base of the throat on the exhaust side at 180 degrees from the top just in front of the throttle slide. This is where the idle mixture is fed in to the cylinder.

Hole 3 is where the air bleed screw goes in.

At idle air is drawn from hole one and the air screw then adjusts the amount of incoming air, this is then mixed with fuel from the pilot jet To provide the idle mixture.

The resulting mixture then squirts out of the very small hole (hole 2) at the front of the throat in to the cylinder.

I found the best way to check for blockage in the whole pilot circuit is to remove the pilot jet and air screw and blow down the air screw hole and at the same time cover the pilot jet hole and the other 2 holes with some combination of fingers and thumbs. You can then lift a finger or thumb from each hole in turn and hear if you get air blowing through.

It's a bit like mastering playing the bagpipes but an effective way to check the circuit for blockage.

This may sound complicated but if you find the holes and study the plenum chamber in the base of the carb it's pretty obvious how it works.

[Seabeowner]

My 78 550K US import is pretty original I think. The clip was also in the second from the top. 90 main jet. (I found some conflicting info on the US site as to whether this was correct) The needle is marked 2949F. PD46C carbs. They were set to run lean and so far it's been a pain in the a***, but even though I have a set of the earlier carbs I,m going to have another go at them for the sake of originality.