Topic: CB750 PD Carbs ('78)

[KB02]

So... I am an idiot.
Just thought I would establish that before going any further into this post.
Also, hello all! It has been a VERY long time since my last post. Life has been busy and, sadly, the '78 750K has been sitting virtually untouched in my garage for the better part of 7 years.    (see point #1 above).

This weekend I undertook the project of cleaning my garage up to get ready for winter and make better use of the new work bench I just built, and the 750 has come back out to be wrenched on once more. Step #1 was cleaning out all the vanish that I let sit in the tank and carbs for the last half decade (again, see point #1). And while the garage smells horrible, my question has to do with the assembly of the carbs themselves. It's a two part question, really:
1.) Which way does the cut out on the throttle slide face? Airbox or intake?
2.) If the slides had been inserted backwards, what kinds of problems might that induce into the running of the engine? Lean surging or hanging idle, perhaps?
... you know... asking for a friend...

[Alan F.]

Welcome back, I have a K8 in the works now too so I'll be reading along with interest.

Edit: I just reread the build thread, lots of innovation and custom combinations in this bike.

How's Simon and Rosco the dog doing?

[bryanj]

Flat side to engine and unless you mixed the slides up they should not fit the wrong way round as there is a locating pin

[TwoTired]

The slide cutaways face the air filter.

Cheers,

[bryanj]

Forgot to add I hope you got the pressed in pilot jets out

[KB02]

Flat side to engine and unless you mixed the slides up they should not fit the wrong way round as there is a locating pin

You might think that, wouldn't you?
That is one thing that really surprises me - There is no locator pin in these carbs. How crazy is that?

And yes, I got the slows out. My one worry on that is that they came out much easier than I thought they would. Should that worry me?

Welcome back, I have a K8 in the works now too so I'll be reading along with interest.

Edit: I just reread the build thread, lots of innovation and custom combinations in this bike.

How's Simon and Rosco the dog doing?

Yeah, all the custom bits makes this bike... interesting to work on. Next one I build up will be mostly bolt on parts if I go away from stock (and lets be honest, its me. I probably will).

Simon is now 11 and quickly becoming a teenager with all the brooding angst that goes with it. Rosco is still hanging there at 12 but becoming a grumpy old man.    We got a new puppy (a bully mix) this spring and Rosco was not thrilled. She challenges him in the chewing department! 

[KB02]

I original asked this questions because I wasn't paying attention when taking the carbs apart. As stated above, they can go either direction. The more that I have thought about it, I really think that I had them assembled backwards. The bike was last registered 10 years ago and has sat mostly untouched for quite some time, so you'll forgive me if my memory is a bit rusty.

On to the second question I posted above: What would the effects of having the slides backwards be on a running engine?

[bryanj]

Dont think it would

[TwoTired]

On to the second question I posted above: What would the effects of having the slides backwards be on a running engine?

extremely poor idle (If it does at all) and awful transition off idle.

The pilot circuit exit is at the slide position toward the engine.  If the cutaway is on that side instead of at the entrance, pressures and venturi effect will be way out of optimum.  The cutaway is supposed to increase velocity over the mains/needle valve exit to provide additional fuel for transition off idle.  Reverse that and I think you'll have a bucking beast to drive.

Cheers,

[Don R]

 It will run bad enough you might take the bike to a pro 750 Honda mechanic. Maybe even the same guy that built it from the crate new and knew the first owner.  How do I know all that?  It's a secret.

[KB02]

Is it odd that I am holding out hope that the biggest problem on this bike was my own stupidity?

As I said, it's been 10 years since I had the bike running. But from what I can remember, the idle was erratic, it would hang like crazy after slowing down, and the plugs read like it was running lean so I just kept throwing in richer and richer jets. I originally dug it out this fall because I had finally decided that it would be better off in someone else's garage and figured that I would significantly increase it's resale value with clean carbs and tank and if it would actually start. Now my hopes are high that I might actually have figured out this nagging problem that has bugged the crap out of me for 10 years! Maybe I'll keep it after all?

Thanks all. I'll report back either way. Hopefully it will be, "Hooray! I'm Stupid!" and not "Crap... that didn't do it either..." Too bad winter is almost upon us here...