Hanging idle please help

[Wenman]

Is it possible for the return spring to bind in its shroud (if it has one )?
[/quote

Great idea and on reading this I got very excited to think it might be something simple as that however as previously mentioned it dosent do the fault when engines off and if it was the shroud I’d expect it to do so both engine running and engine off??

Because it fails to do so when off I don’t believe it’s anything mechanical?

Could be wrong tho, have been many times before!

[Wenman]

Okay so this morning I removed the cables from the carbs ran it and still playing up, then I also removed the pod filters to see if they causing the issue.

Still defective

It seems no matter what I do when I open the throttle slowly raising the lifters only about 5mm they will NOT seat back quickly.

I have done another video which shows the slides themselves very slowly returning to where they should be.

https://youtu.be/yKIJlmy-rHc

Please have a look and see what u think?

Is there anyway of raising the sliders so they don’t go down as far as they do when they slow down by screwing the idle screw in raising the idle but then somehow reduce the idle on the air/fuel screws.

I’m running out of ideas now 😩

[K2-K6]

Ok,  in that direction of "oddness" what have you ended up at when setting the idle mixture screws?

Projection to try and see if if makes a difference,  turn the mixture screws IN a quarter turn from where they are,  this should slow the tickover down ( makes it richer) forcing you to wind up the main tickover rpm control for the carb rack to bring it back up to normal level.

Let us know if that changes it.

The routine I posted a couple back is trying to move it in the direction you are after,  give that a try and see if you get an improvement to assess if it's on the right track.

[blackeagles]

The only thing I can think of is an air leak in the inlet rubbers but when I had the carbs off I inspected them all and they all looked good??

Don’t really want to start throwing money at it when I don’t know what the exact problem is?

Any more help would be appreciated if you guys/girls have any ideas??

Thanks

Alan

this is what i said when i was having the initial problems with my pd42a carb setting (not quite sorted yet).  even spraying carb cleaner/ether on them didn't raise the revs (but took the paint off the brace) but k2-k6 suggested i get my wallet out and i replaced the lot (i didn't realise the 'stacks' in the cleaner are tapered so act a velocity stacks) anyway at least it now runs and when, like you, i sort out the sync and pilot setting it should be all good.

[Wenman]

Right so carbs off.. slides out all cleaned reassembled, slides move and fall freely off the bike, there is zero friction on the sliders, return spring added and they slam shut.

They still very slowly drop when I apply a very small amount of throttle.. this is def being caused by the engine running, maybe it’s characteristics??

Please if anyone has a CB750 can they try running it apply a small amount of throttle and watch how fast the sliders seat?

Maybe I’m just going mad!

Thanks you

[blackeagles]

i don't have that type of carb so cannot test however this video clip (first couple of revs or so) seem to indicate that the carb should snap shut

https://www.bing.com/videos/search?q=honda+cb750+k2+carb+setting&&view=detail&mid=F17208F1C8D28AAFB071F17208F1C8D28AAFB071&&FORM=VRDGAR&ru=%2Fvideos%2Fsearch%3Fq%3Dhonda%2Bcb750%2Bk2%2Bcarb%2Bsetting%26FORM%3DHDRSC3

[Wenman]

Mine operate the same as that and they do slam shut when opened up anymore than 10%.

It’s only occurring when I apply a very small amount of throttle.

I posted a video of it earlier in the feed and you can see where the hang up is

If I open the throttle anymore than 10% the weight and force of the spring slams them shut.

If I apply a very tiny amount of throttle that closing momentum created by spring and the weight etc isn’t present so they are closing but very slowly?

[JezzaPeach]

I’m clutching at straws here but could there be a little suction pulling the needles up in their holes? If that’s not nonsense, maybe allowing more air via the pilots (1/4 turn anti each) might help.

[blackeagles]

so your saying with the engine off they snap shut but with it running thye shut slowly if slightly activated but ok at a larger movement of the throttle.  presumably with cable on and off and if you press them down either running or not they close 'correctly'.  only thing i can think of if everything is running freely it could be the vacuum pressure in the venturi acting against the return spring - is the spring the correct poundage for this carb?

[Wenman]

I’m clutching at straws here but could there be a little suction pulling the needles up in their holes? If that’s not nonsense, maybe allowing more air via the pilots (1/4 turn anti each) might help.

I understand your logic here, however if the lifters were closing fully and the revs hand that could be a cause.

The revs hanging is being caused by the lifters and subsequent sliders are not falling quick enough

[Wenman]

I’m wondering if the return spring is incorrect?

Running out of ideas now

Does anyone have a spare throttle return spring I could purchase? DSS have them as discontinued??

Thanks

Alan

[blackeagles]

part no 16123300004  ebay 401385919944 but you could try using another spring or reducing the existing one

[Trigger]

I’m wondering if the return spring is incorrect?

Running out of ideas now

Does anyone have a spare throttle return spring I could purchase? DSS have them as discontinued??

Thanks

Alan

Sliver do the spring Link >>> https://www.davidsilverspares.co.uk/CB750K2-FOUR-1972/part_221951/

[Wenman]

I’m wondering if the return spring is incorrect?

Running out of ideas now

Does anyone have a spare throttle return spring I could purchase? DSS have them as discontinued??

Thanks

Alan

Sliver do the spring Link >>> https://www.davidsilverspares.co.uk/CB750K2-FOUR-1972/part_221951/

Thanks trigg, currently showing out of stock tho 😩

[K2-K6]

"Is there anyway of raising the sliders so they don’t go down as far as they do when they slow down by screwing the idle screw in raising the idle but then somehow reduce the idle on the air/fuel screws.

I’m running out of ideas now 😩"

Ok,  in that direction of "oddness" what have you ended up at when setting the idle mixture screws?

Projection to try and see if if makes a difference,  turn the mixture screws IN a quarter turn from where they are,  this should slow the tickover down ( makes it richer) forcing you to wind up the main tickover rpm control for the carb rack to bring it back up to normal level.

Let us know if that changes it.

The routine I posted a couple back is trying to move it in the direction you are after,  give that a try and see if you get an improvement to assess if it's on the right track.

This is what the above setting is trying to do.  By turning the screws inward it should make it richer and slow the rpm,  to the point where you have to raise the slides with the master tickover control screw setting, and so bring the throttle slides up a little at idle.