Topic: a little advice on last settings / jetting for carbs

[Chaser60]

1975 CB550. 

- Complete stock air system with Uni foam filter.   
- 4 into 2 headers (MAC I think) with CONE engineering quiet core mufflers.
- Carbs opened cleaned and bench sync'd.   These are 022 carbs with 38  100 jets.   I did not check the clip setting while apart and no doubt this will bite me with a do - over now.   Air screws are currently 1 1/8 out on all four.   Float height 22mm.

Values and timing chain adjusted per manual.   I could not get point gap and timing to be in spec with timing light on 1-4 and 2- 3.   Yesterday replaced points with new.   Gap set mid range of spec and timing now dead on for 1-4 and 2-3 both at idle and full advance.   

It starts and idles fine,  however when fully warmed up I am experiencing hesitation in the mid-range of throttle and while this is totally subjective, it feels like it is running hot.

Things I have NOT done yet.   Vacuum sync the carbs.  Check the float heights with clear tube method.  Plug chops.  Compression test. 

I did pull all four plugs yesterday after resetting the timing.   Plug 1 looks lean.   Plugs 2 through 4 look ok.

Is the next step to vacuum sync, plug chops or something else?   I am a little worried about cylinder 1 being lean and don't want to cook a piston or go chasing jetting changes if not needed.  Any other steps to take at this point?

Thanks

[dave500]

vac sync the carbs,38/100 wont be too lean,check your needle clip the middle position works fine,try and get the ignition spot on and be sure the advancer is working,time the engine at full advance by increasing the rpm till it stops advancing,set the timing there and forget about where it ends up at idle,forget the F mark at idle,run non eth fuel if you can.

[Chaser60]

thanks Dave,

Will be doing some work later today and will double check all of the above.   I think my needle clips are in the stock position, which is 4 down - correct?  I am not loving the idea of pulling those apart, and sooo regret that I didnt check that when I had the carbs apart.   As I remember it, I tried one and started to strip that damn little screw, so I think I wimped out.   Learned a lot on this project.   I wimped out like 3 times on this project and now 3 for 3 on those decisions biting me in the tail.   Wont make those mistakes on the next one.

[lucky]

1975 CB550. 

- Complete stock air system with Uni foam filter.   
- 4 into 2 headers (MAC I think) with CONE engineering quiet core mufflers.
- Carbs opened cleaned and bench sync'd.   These are 022 carbs with 38  100 jets.   I did not check the clip setting while apart and no doubt this will bite me with a do - over now.   Air screws are currently 1 1/8 out on all four.   Float height 22mm.

Values and timing chain adjusted per manual.   I could not get point gap and timing to be in spec with timing light on 1-4 and 2- 3.   Yesterday replaced points with new.   Gap set mid range of spec and timing now dead on for 1-4 and 2-3 both at idle and full advance.   

It starts and idles fine,  however when fully warmed up I am experiencing hesitation in the mid-range of throttle and while this is totally subjective, it feels like it is running hot.

Things I have NOT done yet.   Vacuum sync the carbs.  Check the float heights with clear tube method.  Plug chops.  Compression test. 

I did pull all four plugs yesterday after resetting the timing.   Plug 1 looks lean.   Plugs 2 through 4 look ok.

Is the next step to vacuum sync, plug chops or something else?   I am a little worried about cylinder 1 being lean and don't want to cook a piston or go chasing jetting changes if not needed.  Any other steps to take at this point?

Thanks

 Intake stock. No it is not. With a unifoam filter it might as well be pods with 
tape on them.

Get a stock paper air filter and you will not have to change the needle position.
The stock paper air filter will richen the mixture.

Check for air leaks on Cylinder #1.
 Make sure the intake valve on #1 is closing all the way by checking the tappet clearance. Also check the float bowl for fuel level.

[Chaser60]

Thanks Lucky.  All I meant by stock was that all other elements of the air box are intact and in use, except for the substitution of the foam filter.  As I think of it, I also had to make a foam filter element for the bottom of the air box and used a lawn mover element for that small rectangular part of the re-circulation circuit..

Sorry to ask this, but do you have any tricks of the trade to  check for air /vacuum leaks?  I have heard of people using smoke to check for exhaust leaks, but have never tired that for either exhaust or intake side.

Thanks

[calj737]

Spray some Carb cleaner near the boots to check for vacuum leaks, Bill. It's cheap and decisive.

From your induction mods, I'd suspect rich not lean, so pursue Dave's adjustment advice. I'd also think a vac-synch would be worthwhile before going nuts on the carb adjustments. Then a plug chop to definitively understand the A/F conditions.

[lucky]

Thanks Lucky.  All I meant by stock was that all other elements of the air box are intact and in use, except for the substitution of the foam filter.  As I think of it, I also had to make a foam filter element for the bottom of the air box and used a lawn mover element for that small rectangular part of the re-circulation circuit..

Sorry to ask this, but do you have any tricks of the trade to  check for air /vacuum leaks?  I have heard of people using smoke to check for exhaust leaks, but have never tired that for either exhaust or intake side.

Thanks

A compression check will tell you a lot about the engine air leaks.
Get the stock air filter though.

[Csrgti]

Wouldn't a compression test only indicate air leaks inside the cylinders ( valves, rings and head gasket)?
Is there a way that a compression test can pinpoint leaks in the intake manifolds, if so could you explain how.

[TwoTired]

My first task would be to learn why #1 shows different spark plug deposits than the others.  Vacuum sync would be my first step.  Swap the "different" plug for another position, or replace plugs to learn if that gets them all depositing the same patterns.  If not, compression test, float height, etc.  Did you verify the emulsion tubes were clear and the orings for jets are sealing as new?

The UNI NU-4055 filter works fine.  It is NOT going to cause a single cylinder plug deposit difference.  However, that and the exhaust change might change the ideal pilot screw setting.  Without knowing the exhaust flow difference from stock, I can only guess that turning the air screws inward 1/8 turn might help.

Mark your throttle.  In any gear, from idle speed, the engine should accept without stumble up to one half remaining throttle travel and accelerate reliably (even if not particularly briskly).  That is how the idle screws are set for this model using no-stock configuration.  If the engine stumbles, you need to turn the air screws inward.  if you have have trouble with plug soot fouling with prolonged idle, the air screws need to be turned outward.

There is no good reason why the timing for idle and advance positions shouldn't be identical.  And, if you wish the idle to be smooth with minimum trans gear clack, it better be identical between 1-4 and 2-3 at idle speed.

Without a run time log report, we can't tell if the engine's been sitting for a time.  There could be specs of rust inside holding valve a bit open and rings binding the piston grooves, etc.  A compression test will give a current engine health overview.  If one cylinder has less compression that the other three, you can't expect it to behave like the others and no amount of carb tuning, duct air leak investigation is going to fix the situation.  However, another 100 miles of operation may get all the parts happy with each other again.