SOHC.co.uk Forums > Anorak's Corner
Carburettors with more depth of discussion
DomP:
I must be missing it but I can't find the air screw adjustment procedure in the shop manaul
K2-K6:
--- Quote from: DomP on October 07, 2024, 11:48:55 PM ---I must be missing it but I can't find the air screw adjustment procedure in the shop manaul
--- End quote ---
Unsure of location in manual, but usually it's within a carburettor strip and rebuild section as it deals with optimisation after reassembly. Thats rather than service section.
I haven't viewed all of the manuals, but it's definitely contained in the mix I have.
K2-K6:
To describe the idle setting procedures is worthwhile here to give widened overview.
Caveat:- it's necessary to ensure all the other influences are correctly in specification to make this adjustment valid, ignition, sync, plugs, fuel supply etc. A refined "bench" synchronization is absolutely ideal for this purpose as it introduces no extraneous tolerance of gauge or method into the assembly of carburettor component.
Starting with a base setting of installation in adjustment screw, that 1 1/2 type setting, gives competent running to begin.
Then it requires (working one at a time, for each individual carb) to adjust the screw in giving weaker mixture until you here that cylinder start to falter with some missing beat/firing. This should be indication of the mixture now approaching and then breaching stoichiometric balance. This happens when fuel molecule mix with air/oxygen at 14.7 parts O2 to 1 part fuel. Below which leaves fuel unburnt, above which stops reliable combustion from taking place because there's not enough fuel to burn in tbat mix.
It's effectively using you and the observance of that cylinder combustion as a O2 sensor that you'd expect in a fuel injection setup.
At that point, it directs to then bring the mixture back towards richer mixture by observing a 100 rpm drop in crankshaft speed. This is now the reference point for that cylinder.
Now to correct the overall engine speed if its too high or low with the master idle control screw (the one that winds the whole rack of carb slides up and down) then repeat the same setting process for each successive cylinder to give quantified position on all of the carbs/cylinders.
This routine has now calibrated all of your idle circuit,,taking into account the hardware (bore in carb, jets, screw, vacuum available, fuel content etc.
Its likey, but I've not measured it, that the resulting fuel air ratio at idle will be between 12.7 & 13.7 ~1 ratio that gives the conditions for smooth idle. Aso the ability to bring stable return to idle when throttle is released.
If the normal adjustment on screws on each carb doesn't yeald satisfactory response (usually within 3/4 to 2 3/4 turns out) that shows that something inside that idle circuit design is not as it should be.
Within these idle routing and components, something is causing the irregularities that you are trying to now adjust into range. Usually without successful outcome.
DomP:
--- Quote from: K2-K6 on October 08, 2024, 11:04:21 AM ---
--- Quote from: DomP on October 07, 2024, 11:48:55 PM ---I must be missing it but I can't find the air screw adjustment procedure in the shop manaul
--- End quote ---
Unsure of location in manual, but usually it's within a carburettor strip and rebuild section as it deals with optimisation after reassembly. Thats rather than service section.
I haven't viewed all of the manuals, but it's definitely contained in the mix I have.
--- End quote ---
I found an old post of yours where you explained it very nicely so I'll put it into practice.
Johnwebley:
--- Quote from: Johnwebley on October 07, 2024, 03:16:58 PM ---
--- Quote from: K2-K6 on October 07, 2024, 10:14:23 AM ---
--- Quote from: Johnwebley on October 05, 2024, 04:32:34 PM ---This is really confusing me,
But that's easy,
I recently did some work on my 500,nothing to do with the carbs,
And fitted new carb to head rubbers as the old ones were hard,
Since then, I have had a hanging throttle,
It runs well when cold, but as it warms up ,if I blip the throttle it zooms up to about 4,000rpm,
It can be slowed by pressing the large nut in the linkage,
But why?
I haven't touched the settings,
Help and advice needed
I have the carb sync gauges connected, all read the same,
Sent from my SM-A546E using Tapatalk
--- End quote ---
When the throttle is closed, can you "find" any slack in the exposed cable where it arrives at the carburettor quadrant ? Indication of the twistgrip and cable being not the problem.
Something very small, the liner inside the throttle cable where if turns out of the twistgrip, the inner cable eventually cuts through that 90 degree turn making it non linear in operation.
With the cable removed from bike, and all the inner pulled out the twistgrip end, you can usually pull that little liner out of the cable cover to inspect it. If it's cut through , it makes them quite variable in both actuation and return function.
Honda cables were particularly good in their materials, not so much in reproduction stuff though.
--- End quote ---
The cables are fine,
I even use the "closer" cable to try to drop the revs,
Sent from my SM-A546E using Tapatalk
--- End quote ---
Just an update,
Have adjusted airscrews to 1 1/2 ,
still the same,
But spits back through the carbs when cold,
I had worked on the head, cam etc,
So may have not timed the cam accurately
Will lift the lid and check
Sent from my SM-A546E using Tapatalk
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version