Topic: CB750 K0 Slides-Important Information

[cfairweather]

I have been restoring a 1970 CB750 K0 and was recently testing the rebuilt engine.  It ran ok, but I couldn't get it to idle properly and knew there was something wrong.  After some troubleshooting, I figured out my mistake and I am guessing there are others that have had the same issue.  The slides look the same at first glance, but there are actually two types.
 The left two are different from the right two and be aware that any slide will fit in any carb, so it is easy to mix them up.  The difference is the angle at the bottom of the slides.  On mine, I discovered there is an ID stamped on the bottom of each slide, 153 and 154, and you may have to use a magnifying glass to see the entire number as mine were hard to read.  The 153 type goes in cylinder 1 and 2.  The 154 type goes in 3 and 4.  As soon as I made this change, the bike idled perfectly.

Hope this helps someone.

[Johnie]

Now that is something I never ran across. I will have to pull my slides to see what I find. Mine idles good and it has been a while since I did my KO. I might have even marked them when I took them off as I am a bit anal. Thanks for that interesting info. Looking forward to what others have to say.

[M 750K6]

 What would be the reason for that? I could perhaps see 1 and 4 being paired and 2 and 3 likewise, possibly different airflow from the airbox, maybe even different temperatures, having clear air on the outside. Don't see why left pair are treated differently to the right pair, unless fuel flow may be different? Don't see that really.

Not doubting, just wondering why and whether it carries through into later bikes?

[MauiK3]

Subtle, I also wonder why.

[Lucien Harpress]

Yup, basically one side of the slide is scalloped a bit more on the bottom than the other.  The reason they are "handed" is to keep all four scallops facing the same direction (towards the engine if I remember right, but I could be wrong) while having the ramps for the idle adjust screws in the proper orientations.

The later round-top carb slides are scalloped like this too, but I'm 90% certain all four slides are identical on the K1 and later sets.  Reason being, because the idle is set on those from the top, there's no need for the ramps.  So Honda eliminated them.

[leovich]

Subtle, I also wonder why.

They’re different because 1 and 2 have the idle knobs on the left side of carbs and 3,4 have idle knobs on the right so slides need to match where the ramps for idle screw need to be

[M 750K6]

Got it, thanks for explaining. 👍

[Don R]

 Don't feel bad, around 20 years ago I hauled my bike 30 miles to a known Honda mechanic's shop and paid him to figure it out.  Same deal.
 In my defense, I numbered them on the tops before I removed them so they came like that when I bought it.

[HondaMan]

When I heard about this I went to my set of near-sandcast K0 carbs (still sitting in their box) to look.
Two of the carbs have numbers on the slide bottom like "15(n)" with one being "3" and the other "4". But, the #1 carb only has a "5" on it in the same place, and the #4 carb has a letter stamped near where those numbers are on the other slides.
The intake cutaway on the #1 slide also has a very shortened bevel above the slide.

It makes me wonder if Honda's techs were going to the extent of hand-tuning/balancing the idles on these early bikes, since they hand-fixed so many other parts of them, too? This is one of the reasons my book covers the "production" models of the K1-K6 and only alludes to the early ones here and there: they have so many changes in them it's a surprise to open one up and look in!