Topic: CB550 Idle Screw Adjustment?

[67Fastbackfan]

Recently got my '75 cb550 on the road. Started right up but was having a slightly rough idle and occasional sucking sound coming from 1 and 4 cyl. Also occasionally has issues revving from idle. But other times it's ok? The sucking sound would occasionally show up during cruising while coasting at idle. Started tuning on the idle screw adjustments. Almost all cyl were about 2-2 1/2 turns out. Turned them all the way in during idle and it smoothed out. But... Shouldn't this shut down the engine? I cranked them basically all the way out to see if it made a difference and the only difference was on the 1 & 4 cyl? 2 & 3 no matter the setting didn't seem to make a difference. I cranked them all the way in and turned them 1/2 a turn out and the idle seems to be doing a lot better with no sucking sound.

I guess my question is, should I leave it alone or will having them cranked in so far lead to something else?

[riverfever]

You only have one idle screw and it's on the right side (while sitting on the bike) and about 1/2" in diameter. Sounds like what you're referring to and making adjustments to are the mixture screws (one for each carb and actually on the carb bodies themselves). Two or 2 1/2 turns out sounds like a lot. I don't have my manual in front of me but factory settings were probably closer to 1 turn out +/- 1/8.

[Deltarider]

Fot the CB550K, K1 standard setting of the airscrews is 1¹/₂ +/- ³/₈ out. If bike sat for a long time, there's a good chance pilot jets are (partially) blocked. You could first try an additive in the fueltank, but if that doesn't work be prepared you have to open the floatchambers and unscrew the pilot jets for inspection/cleaning. If you are careful enough and are in the right mood you can do this with carbs in situ. BTW, it's a good occasion to replace the 16 screws by small ss allen bolts.

[flybox1]

Started tuning on the idle screw adjustments. Almost all cyl were about 2-2 1/2 turns out. Turned them all the way in during idle and it smoothed out.

Those are mixture screws, and should be adjusted to aid in obtaining the proper air/fuel mixture in your idle circuit.
Clean your carbs. 
Download the Honda Manual for your bike.  It will really help
http://www.honda4fun.com/materiale-documentazione-tecnica/shop-manual

[Duanob]

Possible massive vacuum leaks? If the ide screws are all the way in you're not getting any air via the idle screw jet. If it still runs you're getting air from somewhere else. Maybe the sucking sound is a clue. Ever change the o-rings between the intake manifold and the head? Just spitballing here...

[Deltarider]

If the ide screws are all the way in you're not getting any air via the idle screw jet.

Remains to be seen. Note that the airscrew on this model is hollow and crossdrilled.

[67Fastbackfan]

No vacuum leaks to speak of. All boots and o rings on the intakes were replaced along with the screws for sync'ing. I replaced the stock air filter and exhaust, so I'm guessing that it's running too lean. Plug is "slightly" light ashy but not crazy.

 I did notice that even though the bike runs better with the mixture screws all the way in it does not want to start. Not getting enough air if the choke is engaged. Crack the choke and it will start right up. The carbs sat for a year, I've been running some seafoam in the tank but I'm thinking its time to take them off and give them a good cleaning. I have a very minor leak coming from cyl 3 bowl so I'm replacing gaskets and I'm going to go up a few sizes on the jets and see if I can get it sorted out.

[flybox1]

No vacuum leaks to speak of. All boots and o rings on the intakes were replaced along with the screws for sync'ing. I replaced the stock air filter and exhaust, so I'm guessing that it's running too lean. Plug is "slightly" light ashy but not crazy.

 I did notice that even though the bike runs better with the mixture screws all the way in it does not want to start. Not getting enough air if the choke is engaged. Crack the choke and it will start right up. The carbs sat for a year, I've been running some seafoam in the tank but I'm thinking its time to take them off and give them a good cleaning. Good, this should have been done first.   ;)I have a very minor leak coming from cyl 3 bowl so I'm replacing gaskets and I'm going to go up a few sizes on the jets and see if I can get it sorted out.  Why up jets when you havent tested that you need them?  Clean your carbs, do a good bench sync, and if all other maintenance items are done, vacuum sync them.  THEN....start testing to see if you need to re-jet.

[harisuluv]

When you say you replaced the stock air filter and exhaust, does that mean you have a non stock setup or that you replaced it with the stock parts. 

Your setup is hard to follow, I don't know what you actually have as far as modifications.  The mixture screws all the way in is not what you want.  Also, as mentioned, you don't adjust the idle via the mixture screws.  There are 4 individual adjust screws for that (NOT THE MIXTURE SCREW) and then you can adjust them all at once with THE idle screw.

Some pictures would help.

[67Fastbackfan]

The carbs came off a well running engine so there was no dire need to open them up. I thought with the modifications (Pod filters and 4-1 open exhaust) I was going to have to re-jet anyways, so I wanted to install the carbs and see how they did. I'm not trying to change the idle speed, just tune the carbs to get the most out of them. With the mixture screw, you can see how it effects the idle as the rpms will increase or decrease based on the position. So I went to each carb and attempted to find  the highest rpm possible with the mixture screw. They all did the best with the screw all the way in. However, when cyl 2&3's adjustment screws were turned in and out there was no change. Only change came from cyl 1&4

[Deltarider]

So I went to each carb and attempted to find  the highest rpm possible with the mixture screw.

It's been told many times in this forum that that isn't right. These carbs do not have acceleration jets and all 500/550s need a relative rich idle. I can find a highest idle very easily and the engine will purr like a kitten at idle but it will pick up poorly and acceleration will be very bad. Set the airscrews at what Honda recommends for a start and work from there.

[harisuluv]

The carbs came off a well running engine so there was no dire need to open them up. I thought with the modifications (Pod filters and 4-1 open exhaust) I was going to have to re-jet anyways, so I wanted to install the carbs and see how they did. I'm not trying to change the idle speed, just tune the carbs to get the most out of them. With the mixture screw, you can see how it effects the idle as the rpms will increase or decrease based on the position. So I went to each carb and attempted to find  the highest rpm possible with the mixture screw. They all did the best with the screw all the way in. However, when cyl 2&3's adjustment screws were turned in and out there was no change. Only change came from cyl 1&4

I don't know how many times the same thing can be said to you.  I'm not sure why you even have this thread started if you are just going to dismiss everything people say to you.  At this point I'm going to exit the thread.

[flybox1]

The carbs came off a well running engine so there was no dire need to open them up. I thought with the modifications (Pod filters and 4-1 open exhaust) I was going to have to re-jet anyways, so I wanted to install the carbs and see how they did. I'm not trying to change the idle speed, just tune the carbs to get the most out of them. With the mixture screw, you can see how it effects the idle as the rpms will increase or decrease based on the position. So I went to each carb and attempted to find  the highest rpm possible with the mixture screw. They all did the best with the screw all the way in. However, when cyl 2&3's adjustment screws were turned in and out there was no change. Only change came from cyl 1&4

YOU are trying to achieve the proper air/fuel mixture by (visually) indicated rpm? 
Lemme know how that works out for you.