Topic: Pilot air screws. Do they adjust sync?

[Dos]

I have a feeling one or more of my mixtures on my carbs is richer than the others.

If I adjust the pilot screws will this also affect my sync?

[ekpent]

 No. Slide height effects the synch.

[bryanj]

Correct but adjusting the mixture will affect how that cylinder runs which might alter the balance

[Dos]

The balance of the carb sync? Or the balance of how each cylinder fires? I’m confused now, so it can affect the sync of the carbs?

It seems one or two of the screws go in more than the others and it makes it hard to identify if the circuit is completely closed or not. Is this normal?

[goodtryer]

There should be a spring, and on some models also a washer & o-ring, behind/under each screw. Make sure you're not missing any of the parts. That could account for the different feel. Could also be dirt/grime in one versus the other...

Good luck!

[caluser2000]

The balance of the carb sync? Or the balance of how each cylinder fires? I’m confused now, so it can affect the sync of the carbs?

It seems one or two of the screws go in more than the others and it makes it hard to identify if the circuit is completely closed or not. Is this normal?

Dos, it has been quite some time I worked on a CB350F. I would set the air screws as Honda prescribes and concentrate on the syncing if needed, IF. When you have the bike idling, you can check the idle circuits by turning the screws of each individual carb - one at a time ofcourse - all the way in and then let's say two turns out. This is to check it is still of influence. When the circuit is open, you will notice the rpm either drop or rise, be it slightly. That's OK. Then go to the next to do the same. If rpm does not change in this procedure, it could indicate the idle circuit is not open and inpection is needed. It is a simple test.

That is because it is just the idle affected. Carb sync is done at a higher rpm bypassing the idle circuit.

[Deltarider]

Caluser is a bit too quick. I hadn't finished editing my post. Forgive me. I'm not a native speaker and sometimes need more time.

The balance of the carb sync? Or the balance of how each cylinder fires? I’m confused now, so it can affect the sync of the carbs?

It seems one or two of the screws go in more than the others and it makes it hard to identify if the circuit is completely closed or not. Is this normal?

Dos, it has been quite some time I worked on a CB350F. I would set the air screws as Honda prescribes - I seem to remember ⁷/₈ of a turn out - and concentrate on the syncing if needed, IF. When you have the bike idling, you can check the idle circuits by turning the airscrew of each individual carb - one at a time ofcourse - all the way in and then let's say two turns out. This is to check it is still of influence. When the circuit is open, you will notice the rpm either drop or rise, be it slightly. That's OK. Then go to the next to do the same. If rpm does not change at all in this procedure, it could indicate the idle circuit of that carb is not open and inspection is needed. It is a simple test.
I would sync at around 1500 rpm. You can adjust by turning the big idle adjuster.
In principle when the mixture of a carb differs from the others, it will not influence the vacuum notably. The corresponding piston is forced down anyway - by its collegues on he crank - and that creates the vacuum.
Since syncing carbs in this forum is epidemic, let me show you what the owner's manual says. I've done tens of thousands of kms without ever needing to sync and in my memory I cannot recall a CB350F that needed it, but that's just me.

[bryanj]

Correct, and when i worked in a dealership i would not do just carb sync, its the last part of the service
Points gap
Timing
Tappets
Cam chain
Carbs

[caluser2000]

Doing a proper carb sync with a manometer can reduce excessive clutch rattle and the like.

I couldn't believe it the first time I synced the CB550Fs carb. Rattle to almost complete silence.

[Deltarider]

Bryan did more than Dutch dealers did. Unless customers asked specifically for a sync, it was common practice to do the other items and in the end start the engine, rev it a few times, listen and then decide whether a sync was needed or not. They had good reason for that: doing a sync in most workshops implied moving the bike to another spot to not hinder their collegues with noise and fumes. Nowadays workshops may have perfect exhaust extraction equipment (if that is the correct word). In the 80s I remember having seen only one that had it. Employees tried to move around bikes as little as possible, which is not a pleasant exercise. This manoevring became even more a problem when bikes got heavier and heavier (weightier?). Good thing was, if they had not performed a sync, you wouldn't find it in the bill either, which I cannot say of the Mercedes-Benz dealer, who, everytime I brought my 190 'Heckflosser' to be serviced, afterwards always presented a bill that stated the car had been 'at the Sun tester' followed by the cost, written with a fork.

[caluser2000]

Carbs components wear after a lot of usage going slightly out of sync over time.

[Deltarider]

Which components do you have in mind? Below some of carb parts that did over 135.000 kms. No wear at all. 
What I have replaced are the little O-rings around the main jets, the float bowl gaskets and that's about it. Even the O-rings at the T-joints are still the ones Keihin has put in. Ironic, because I have a lot of spare carb gasket sets since Honda rewarded me with 4 sets after I reported them there was something wrong with 
the gasket sets 16010-323-305*. My four gauge synchro set I've donated to a friend as I have developed my own method.
* http://forums.sohc4.net/index.php/topic,90925.msg1017076.html#msg1017076 and
   http://forums.sohc4.net/index.php/topic,90925.msg1017309.html#msg1017309

[caluser2000]

LOL they are in the float bowls emerst in fuel and have nothing to do syncing the carbs, just fuel flow and level I was reffing to slides jet lever arms, shafts and pivots etc, etc.....You know  the things that go up and down n stuff.

Over time/use the sealing rubber can rot or get damaged and let crap in the pivot shields.

[Deltarider]

LOL they are in the float bowls emerst in fuel and have nothing to do syncing the carbs, just fuel flow and level

As if I didn't know. Maybe you remember, I asked you what parts you had in mind. Because, frankly, I didn't have a clue what you were referring to, so ignorant little me thought: let me start with the parts that have seen most of the fuel. Those are the parts I showed. To begin with, see? BTW 'Emerst in fuel' is not what is relevant here. The fact that each part shown, has seen 2000 liters of gasoline come by, however is. See what I mean? What you refer to, is static, I choose the dynamic aspect. But make no mistake, I'm happy to know, you had such a good laugh, hahaha.

I was reffing to slides jet lever arms, shafts and pivots etc, etc.....You know  the things that go up and down n stuff.

Ah, now we understand what you mean: things that go up and down. You can rest reassured. A well respected member of the German site has taken his set of CB500 carbs apart to the last and tiniest parts possible and has published a serie of astonishing videos. These videos are the best I have seen on the subject. It's a total of around 4 hours, dissassembly and reassembly and, guess what, in the process he has solved the question I have had for years: how did Honda sync the carbs at the factory? Isn't that wunderbar? Oh, I almost forgot. The things that go up and down? They live forever and our German friend found that an off sync hardly originates there if ever. Good news, don't you think?

Over time/use the sealing rubber can rot or get damaged and let crap in the pivot shields.

Don't we know it, don't we know it, but thanks anyway for reminding us. Anything else we can help you with, Sir? I mean so far your posts have been an ab-so-lute treasure. Time for us to return the favor, don't you think?

[caluser2000]

Before I even bought a motorbicycle, well before the interweb needless to say, I bought a copy of the 1978 edition of the Motorcycle Repair Encyclopedia by Clymer Publications. I recommend other riders, old and new, get a copy and read it. It has sections describing how verious components on a motorbicycle function in a very easy to undand way.

I also love Monty Python like responses so thank you very much for humoring me

That is all the reward I need.

Now I'm for a 400km plus ride on Goat my XF650. Have a good evening, afternoon, night or whatever my good chaps.

[Dos]

So the pilot air screws only affect air/fuel mixture ONLY at idle?

[caluser2000]

So the pilot air screws only affect air/fuel mixture ONLY at idle?

Idle until around 1/4 throttle or so.

[Deltarider]

So the pilot air screws only affect air/fuel mixture ONLY at idle?

Good question, Dos. The views are mixed. On my CB500 the slow jet is still of influence, even at Autobahn speeds. I have tested this and my mec at the time, who owned a CB500 himself, was right. What people tell you, is always from the book, often 'substantiated' by diagrams. This is all theory from the books. A good manual will always warn that there is overlapping and guess what, it is exactly that what people forget first. The diagram that shows best what my bike does, is below and you see that the slow jet is still of influence in the high. Sorry, but I don't know what it is like for your CB350F. If you want to do a plug chop, limit yourself to just one, at your most common cruising speed. In many fora there's a lot about having the idle perfect. It is as people instead of riding, are going to sit beside the bike and enjoy that perfect idle.
Some will advice you to do plug chops at various throttle openings, but IMO, it is all theory from the books and it involves a lóóót of work.

[caluser2000]

A straight answer rather than a book sized reply is what the OP is after Deltarider.

[Deltarider]

A straight answer rather than a book sized reply is what the OP is after Deltarider.

Did he tell you that?

[caluser2000]

That how one deals with tech questions. The easier understood the better.

If a person asking the question is not technically minded and one starts rambling on about this jet,that slide, the amount of vacuum slide blah blah blah.. they will just roll there eye up, think "here we go again" and go to sleep.

If you had done tech tutoring you will know this.

[PeWe]

All air jets/leaks on each carb affect the mix and balance.

If synched with all these errors it will become unbalanced when fixing these errors. Time for another synch.

Deltarider made me to remember my "carb" rides on my K2 2019. Screwdriver for the air screws in my pocket for adjustment beside the road during a 150km ride.

I noticed when I verified my CB750 carbs that air screws affected +100kmh crusing speed. I opened them extra much to really find out their area. Bike acted as time for reserve when opened 1 1/2 turn instead of 1 turn.

Easier to adjust when I knew what to look for and which area

At that speed throttles are not much opened. To get there another thing open more using the needles.

I attach another pic of jets working area that look strange but after some jetting is clear information.

[caluser2000]

That is a clear concise diagram PeWe. Good on you.

See Deltarider that is how it should be done. Not screeds of ramblings.and random links that will confuse the OP.

[Dos]

Thank you all for the information I really appreciate it and I hope it can help others too!

I have my carbs synced pretty good so I’m going to leave it alone..

I do feel the bike runs alittle rich but the 350f gets up to higher Rpms quicker which makes me believe it would really only affect that idle to 1/4 range.. and I’m okay with it being alittle rich at idle..

Alittle white smoke will come out the back at idle when I rev but when I’m cruising there is never any smoke or anything and she runs great.

Yes when I start up it can be alittle clunky because my points are also adjusted to be correct at full throttle but after  warmed up everything is perfect.

[caluser2000]

Great job! well done Dos.