Hanging idle please help

[Wenman]

Okay so here’s the problem..

Honda CB750 k2
Stock carbs
Pod filters (don’t kill me)
4-1 (again don’t kill me)
Standard idle jet
+4 on the main jet
Toming correct
Cam chain correct
New coils
New leads
New plugs
New points
New condensers

Bike runs okay, pulls well above 2500rpm suggesting the main jet is okay, really bad idle and running very rich so I put the stock idle jets back on.

The main issue I am getting is the revs hang around 2500/3000 rpm when at a stand still.

I’ve put them on a vacuum balancer which was impossible as I’m struggling to get the bike to run at idle.

Everything seems okay on the carbs, they were fully dismantled cleaned new jets, seals, float heights done etc.

The throttle return spring is new and if anything on the heavy side.. after holding the throttle open for 3 miles of 50mph my hand was hurting 😂

If I apply A downward pressure to the tops of the carb lifters and blip the throttle it returns quickly to idle every time .. Almost like Ive made an error when putting them back together?
It feels like they are not closing properly?

I know this could be a multitude of things but was wondering if anyone has experienced this and it was a stupid error made when putting a set of these carbs back together??

Thanks for your help

Alan

[Johnwebley]

Have you air leaks between carbs and head?


Try removing the pods and checking.

You could see if the slides are dropping correctly.




Sent from my SM-A750FN using Tapatalk

[Wenman]

I’ve sprayed the inlet rubbers with carb cleaner and didn’t notice any increase in rpms?

Also slides are all seating correctly I believe?

Thanks tho

[K2-K6]

Do you have both throttle cables fitted?

If so,  can you bring the idle down by "forcing " the twist grip closed?  ie. Rotating it clock wise to make the secondary cable work.

If it closes off the high revs by doing the above,  have you tensioned the normal throttle  cable adjustment too much as it should have about 10 degrees of rotational slack at the twist grip.  This would also make the throttle really heavy too if it's not set correctly.

[Wenman]

Do you have both throttle cables fitted?

If so,  can you bring the idle down by "forcing " the twist grip closed?  ie. Rotating it clock wise to make the secondary cable work.

If it closes off the high revs by doing the above,  have you tensioned the normal throttle  cable adjustment too much as it should have about 10 degrees of rotational slack at the twist grip.  This would also make the throttle really heavy too if it's not set correctly.

Pushing the throttle grip forward does not reduce the revs sadly...


I def have play about 10 degrees at the throttle grip. I can see a small amount of slack in the ‘pull’ cable at the carb rack but unsure on the ‘push’ cable? I’ll have a look

[K2-K6]

Push cable usually has no adjuster,  so just fit and leave.  But that one shouldn't give you a problem unless something is misplaced on brackets.

As it has an affect when you push the top of slides it may be that there's not a parity of the slide home position from assembly. Are you familiar with Bryan's bench synchronisation method?  As that should remove an error like that if present.

[Wenman]

Push cable usually has no adjuster,  so just fit and leave.  But that one shouldn't give you a problem unless something is misplaced on brackets.

As it has an affect when you push the top of slides it may be that there's not a parity of the slide home position from assembly. Are you familiar with Bryan's bench synchronisation method?  As that should remove an error like that if present.

No? Happy to whip the rack off and go through a proper sync.. where can I find that document please??

Thabsk

[K2-K6]

http://www.sohc.co.uk/index.php/topic,17769.0.html

It should (it does) remove any discrepancy that inadvertently arises from reassembly of the carb rack to leave the slides in correct position relative to the single hand adjustable idle screw for setting overall tickover speed.

Afterwards,  I'd not try anything with vacuum gauges until you've got the jetting more competently in range.

[K2-K6]

This thread is worth a read too as it looks specifically at accommodations for running without air filter box etc.

http://www.sohc.co.uk/index.php/topic,22031.0.html

It'll be interesting to hear how you get on with it.

[Wenman]

This thread is worth a read too as it looks specifically at accommodations for running without air filter box etc.

http://www.sohc.co.uk/index.php/topic,22031.0.html

It'll be interesting to hear how you get on with it.

Thank you.. I think this is def the best starting point! I’ll be sure to get back and let you know how I get on!

Alan

[Bryanj]

I know i wrote it but it works and if all the mechanical service items are right i find the vac gauges are normaly within tolerance. Idealy if you have done all this and it runs ride it round till next service due, 500 if engine rebuilt 1500 if not, then do vacs AFTER doing rest of service items.

[K2-K6]

I feel it's the best way to set them correctly Bryan, and probably better than vacuum gauges as it effectively calibrates each separate carburettor with exactly the same reference tool as opposed to introducing any gauge to gauge tolerances into the carbs.

It also very neatly has the advantage of being able to synchronise the carbs without any outside influence from the other components, which allows synchronisation to be taken out of the equation in problem diagnosis, and proceed with assurance that's not part of any running issue.

A very accurate way of achieving it.

[Wenman]

Push cable usually has no adjuster,  so just fit and leave.  But that one shouldn't give you a problem unless something is misplaced on brackets.

As it has an affect when you push the top of slides it may be that there's not a parity of the slide home position from assembly. Are you familiar with Bryan's bench synchronisation method?  As that should remove an error like that if present.

Thank you so much!! And thanks to you Bryan as well..

So last night I whipped the carbs off and bench synced them using a red tipped welding electrode 1.6mm (1/16) adjusted all the floats again and went through the jets with a guitar string.
Popped them back on and it’s purring like a kitten.. idle drops back down responsively and it’s sounds great!!

I have the air/fuel mix screw out 1 turn and it seems bang on!

Not had chance to get her on the open road Yet but it’s a far cry from what I was dealing with!!

Once again this forum comes to the rescue! What would I do without you guys!
If you lived closer I’d get you a pint!!

I’ll keep you posted after the run out but needless to say I am very excited!!!

I’ll be clapping for you guys on Thursday night!!!

Cheers

Alan

[Wenman]

Okay so went out for a ride today.. it seems a lot better but still getting the occasional hang up??

What is going on.. I’m at breaking point now.. feel like I’ve tried everything and not sure what direction to go.

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

[hairygit]

Unfortunately as you well know, pods are ALWAYS a compromise when it comes to carb set up. Honda spent a lot of time on R&D of the carbs/filter set up to suit the engine and standard exhaust. You are probably about as far as it can be sorted in it's current form, incorrect filters and incorrect exhaust both play such a huge part in the overall running characteristics of the engine. There is a school of thought around using part of the standard airbox to carb rubbers to act like a bell mouth inside the pod filter. It does something to help sort the airflow through the carbs, but I have no practical experience of this, but a couple of others on here have. Finding their posts may be the next move, rather than keep throwing money at it with no real benefit.

Sent from my POT-LX1 using Tapatalk