Carbs Install

[Martin6]

Hi,

As mentioned in a previous topic, Im looking into why my new 750K6 is reluctant to tickover and run, particularly no.4, along with a stiff throttle that won't return on its owm. The ignition / timing looks ok. Plugs will be replaced.

I've removed and cleaned the carbs and fuel lines. I found 2 things;
-Floats were set at around 30mm above the bowl rim. So maybe it was lean? I've put it to 26mm and will watch out for leaks!
- I was unable to see through two of the slow jets (one was no.4). Hopefully, now all clean.
I'm not familiar with Keihin, nor multi carbs set ups. Im used to single Amals!  At this stage, I only cleaned what I could get to from the float bowl without dismantling them from the gantry system. I'll replace the fuel, the tank is very clean.

I'll crack on this morning. A couple of questions:

I know the carbs were not synch'd prior to taking them off. Is there a good method to getting a base setting on all 4, before re-installing? I have vacuum guages for once it's running (that will no doubt, be fun and games!).

The issue with the throttle not springing back remains a mystery. Cable run is smooth arcs. They were a little, very slightly, stiff.  I don’t think this was the issue. I've flushed them through with silicon lube. They are now nice and light. Off the bike, the throttle movement on the carbs gantry is very stiff. Im not able to shift it manually. On the bike, once the cables were removed, they did operate and spring back. The springs look ok. Should I be lubricating something, or easing any clearances? Is there perhaps a 'usual cause' for this?

Thanks, Martin

[Johnny4428]

Hi Martin, I’ll give it my best shot until someone that has more knowledge comes along. With the idle adjust screw backed off to ensure fully closed sliders, viewed from the intake side of carbs use a plastic WD oil delivery tube or similar ad Nurse Julie suggests and set each slider in turn to get uniformity accross the four. This is the tried and tested bench sync method which can be tweaked with bike running and a vacuum sync.
The carb throttle stiffness, have you disconnected throttle return spring to see where the problem lies? Make sure all clean and no binding with the air intake sliders.

[McCabe-Thiele (Ted)]

A very basic thought is the twist grip nice and free, the one on my 500 was quite stiff when I removed the twist grip the tube was split causing binding.

[K2-K6]

Accurate bench synchronisation of the carbs is easily as good as later "gauge" methods, they don't hold superiority over diligent setting in the first place. Once you have set them off the bike, made sure that you can close the slides fully by turning down the master tickover screw (the big one that controls idle rpm ) confirmation that you can modulate right down to zero on the carb bank, then that's good enough to run.

It holds advantage in diagnosis too, in that if there's fault of ignition or jets impaired/worn then it allows you to see that error rather than chase your tail by adding inappropriate adjustment to carb balance.

Worth stating the purpose of any multi carb balancing, that is to ensure the slides and hence air volumes are the same under full load, it's not a method for trimming idle smoothness, just coincidental that the idle should be smoother when the slides are set at parity.

Individual cylinder denand AT IDLE is emphatically set by adjustment of the low speed mixture circuit AFTER the slides have been correctly set. There's clear information and routine in Honda's manual that describes this schedule.

[Martin6]

Thank you. All very encouraging 

The WD40 spray tube suggestion, im thinking all adjustment just done with what the manual calls the 'adjuster screw' above the top of each carb?

I checked the handlebar throttle tube, the action seems fine. That's all back together awaiting carbs to connect up the cables. Before connecting the cables, pushing on the 2 large U shape castings on the gantry, it seems to open and spring closed OK. Maybe just needed the cables lubing. I'll try it, before I get new cables.

Edit: With the master tickover screw fully out, all slides are fully down, as I raise the tickover screw, the slides all seem to start moving in unison. A WD40 straw is a fraction too large to fit into the cutaway on the intake side. I'll adjust the tickover screw to allow that and start the bike from there. Just have to get them back on now!

Cheers, Martin

[K2-K6]

Silicone oil or grease only for the cables, else you'll get problems.

There needs to be enough slack in pull cable such that it doesn't go tight when turning the steering from full lock to opposite. Seems loose in absolute terms, but needed to avoid a conflict between the two cables that will also make throttle action difficult.

[Martin6]

Yes, silicone used. I will adjust the lower cable for initial slack. Thanks.

[Martin6]

Strange. As soon as I connect the throttle opening cable, the carbs don't close. Also, the return / close cable seems far too short. As soon as it is connected even at its loosest, it is not allowing the throttles to fully close, even manually. There's not enough cable length.

Ive rechecked routing and the bar mechanism. I'll have another look tomorrow, I may be adjusting it all wrong. I've ordered new cables anway.

So, that was the dull bit. I was naughty and removed the return cable and went for a short ride. Fantastic. Handles better than I expected, sounds great. The bike is starting, ticking over, running on all 4. Idle below 1500rpm is lumpy but smooth above that and I sense it wants to pull more at 4-5,000rpm. Pretty sure a carb tune would sort it. However, the rear brake pulses badly. So that's next on the list 

[Nurse Julie]

Is your K6 a UK model with lower handlebars or a USA model with the high bars? Have you got a photo of the bike?

[Martin6]

It's a UK bike. Registered June 1977. K6 engine and frame numbers. Lower UK bars. The standard cables should work.

At the bar end, the throttle tube looks old, but undamaged. It rolls smoothly.

I think the gantry is ok. At the gantry end the max slide lift is about right (just under 33mm) and the 'overcross stop adjustment' is in spec at about 3mm. The springs are strong and look fine.

[Nurse Julie]

OK. If you need any photos, cable routing etc, just shout as we have a UK K6 here.

[Martin6]

That's very kind, thank you.

[Martin6]

I might have found the issue for the cables. Reading the manual, there was a throttle grip adjuster on the underside of the righthand switchgear. This was discontinued from K4s. Mine has the screw adjuster, so it may be an earlier switch set. Does that mean the cables will need to be different?

[Nurse Julie]

I might have found the issue for the cables. Reading the manual, there was a throttle grip adjuster on the underside of the righthand switchgear. This was discontinued from K4s. Mine has the screw adjuster, so it may be an earlier switch set. Does that mean the cables will need to be different?

No, the cables will be the same. Make sure the screw isn't wound in to tight thus causing impingement
Just a thought, has someone glued the throttle tube on, as this can cause stiffness as the glue will be pushed down to the end. Don't ask how in know this 🙄🙄🙄🙄
Edit, forgot to ask if you have the cable routing correct for a UK model as its different to a USA model.

[Nurse Julie]

I've taken a photo, this is our UK K2 but the routing is the same for the UK K6.