idle jet differences , 069's

[fogrider]

Looking at carb kits for sale for the CB550f, there seems to be two types : an air screw that is solid paired with a long idle jet, then a hollow air screw with a side hole in it as well with a smaller bodied idle jet. My 1976 F1 has the solid air screw pairing and as I cannot get rid of the huge bogging down just above idle, I wonder if they are the right ones ?

I have done all the usual things - points/dwell, ignition timing, advancer OK, fuel level Ok and it idles well and reacts to air screw changes. It's not too bad after several miles and warmed up, but from cold it just won't play off idle without full choke but then, after clearing up and revving OK it ,obviously, goes way too rich.

The carbs have been stripped and cleaned ( they were OK as it happens ) but I seem to be missing something, probably obvious !

Any pointers very welcome.
Regards all, Terry.

[deltarider]

The solid type airscrews and the long jets are the right ones for your model. Genuine Keihin jets have the star like K logo stamped. You may want to consult the overview attached. Generally speaking the chokes will be fully opened again before departure but you will need a raised idle for the first two km. Some keep the grip twisted for this, as suggested in the Owner's manual, others use the big idle adjuster which they readjust at say the second traffic light. Do not expect a good acceleration from a stop with the throttle yanked open more than halfway.

[fogrider]

That's excellent, clears up the thing about hollow tip and solid. It runs as though a smaller cutaway would be better but they're original and in good order.  Honda knew best I'm sure.
I spotted a reference to fuel levels later last night, someone had checked with a clear tube - 3mm below fuel bowl top.
Might have a look at that out of interest.

Thanks Deltarider, very useful info.

[deltarider]

To verify correct fuel levels, you may want to use the simple method.described here: http://forums.sohc4.net/index.php/topic,185754.msg2151647.html#msg2151647

[Trigger]

The solid type airscrews and the long jets are the right ones for your model. Genuine Keihin jets have the star like K logo stamped. You may want to consult the overview attached. Generally speaking the chokes will be fully opened again before departure but you will need a raised idle for the first two km. Some keep the grip twisted for this, as suggested in the Owner's manual, others use the big idle adjuster which they readjust at say the second traffic light. Do not expect a good acceleration from a stop with the throttle yanked open more than halfway.

The information is incorrect: keihin air screws can come with or without holes 


[ Guests cannot view attachments ]

[deltarider]

Can you show us where that was denied? It's my habit to post all information thus that it can be falsified by anyone. So far I have not received additions/corrections concerning the carbs. overview, nor the method for verifying fuel levels. I'm always open to it and will be happy to add or correct anything when needed.

[fogrider]

My idle screws look as old as the carbs so I assume they have'nt been changed. It ticks over fine too so it looks like the solid ones are correct.
Have done  the clear tube fuel level already, between 3 and 4 mm so possibly OK. Like your drain down quantities check idea, cup of tea and next job !

I can't find any reference to what cutaway these slides are, I'm sure a smaller cutaway will cure it, but what's the original ?

Regards all, Terry.

[K2-K6]

As already mentioned, they can be quite cold blooded from that period as they started to grapple with emmisions focus that was more related to fuel supplies and oil prices etc.

Where have you got the airscrew set?  It can be beneficial to go a more little toward rich than what you'd consider ideal.  It brings the idle circuit up sooner as you lift the slides and may just be enough to encourage more smooth transition. Worthwhile to do a comparison.

[K2-K6]

"I can't find any reference to what cutaway these slides are, I'm sure a smaller cutaway will cure it, but what's the original ?"

As far as I'm aware there's no alternative slide cut available,  but agree it would be something the could clean this area up by inducing raised initial vacuum just as you open the throttle.

One way of moving it slightly that way would be to go one size (smallest step) up on idle jet, then you'd have to run with the airscrew further out to stop tickover being too rich but get quicker ramp up in volume as you start opening the slide.  Potentially the opposite side round the same square to changing slide cut.

Something they appear sensitive to also, some markets had different airbox cover I believe that affect carburation and so worth checking for oddity there.

[fogrider]

Thanks  for that latest, I have tried a richer idle setting and it did make a small difference, at least it demonstrated that that is where the issue lies.
I have thought about turning a half mill off the bottom of the slides then packing the needle up the same . It's a no going back step !

Dare I do it ?
Must price some slides up to see if it's worth a gamble.

By the way , I tried Deltariders fuel drain check, 50cc per bowl result. Looks like fuel levels are OK.

[K2-K6]

I'd look at the slide question like this;- effectively you're trying to increase the vacuum at lower slide position to pull more fuel through the existing idle jet specification, balanced by the air jet for mitigation.

And so, if you increase the idle jet size,  then the same (existing vacuum) pulls against less resistance in drawing fuel up from float bowl, again mitigated by the air screw setting. In essence the same or close to it as changing the slide, but reversible ultimately.

In addition, if you drop the needle one notch this too would subtract fuel that the idle circuit adds higher up the range. Ultimately it should "fatten" just the transient above idle response while leaving the rest alone,  which is what it appears to need.

[Bryanj]

Dont think ive ever seen slides for sale

[fogrider]

CMSL list them, 73.5  eur each plus plus. They list USA and UK , same part number . Not shown at Silvers.

Looking at ebay, there are Keihin slides quite cheap in the USA, but the adverts don't make it clear exactly what they fit. There is a choice  of cutaway though, which looks promising.

Work in progress, someone somewhere has some, but I'm determined to try a smaller cutaway. I'm sure it's the answer to this seemingly common problem. !

[deltarider]

Before you undertake drastic measures, could you inform us some more like on air intake? Pics are welcome. I think it's odd you need full choke at first and then, when warmed up, engine bogs down. IMO something is not standard. Are you sure brassware is original, that the little O-rings around main jets are still OK and seal well? Is airfilter element OK or has it been wet?

[Bryanj]

You say cmmn problem but not one ive come accross ona factory standard bike