Topic: 77 Cb750k carb question

[nmarshall87]

So after a series of dealt with issues involving a stuck throttle on my bike I've pinpointed two issues:

1. Corrosion on the throttle shaft was keeping the slides in the carbs from moving.

2.  The #1 carb slide was actually stuck in the shaft and won't go back in without excessive force.

So to my limited (and growing!) knowledge I'm thinking the carb would have to be rebored for the slide to fit since I tried another slide and had the same issue and there doesn't seem to be any corrosion/gunk stuck in the bore. Any ideas?  I really don't know if reboring 1 carb 1mm would be worthwhile so I'm looking into possible buying another set of carbs altogether.  Does anyone know if the stock carbs from a 750f will fit a 750k as I found a set on craigslist?  Any and all help is appreciated!

[gnarlycharlie4u]

The F carbs of the same year will work fine. You will probably have to re-jet them though.

As for repairing your old ones... I don't imagine that "boring it out" is gonna do what you want. I mean... I don't think that the carb body just sporadically shrinks. Maybe it was crushed, or the slides were bent or something?

You also may have scored the walls of the carb in removing the slide. This could prevent proper movement.
Look and see. If that's the case I'm not sure where to go from here... maybe you could get away with some finesse and a wire wheel on a dremel.

Maybe just try a really good cleaning first?
Electrolysis or a sonic clean is what I would recommend. Be sure to take everything completely apart (every gasket) before you do though.

Good luck!

[KingCustomCycles.com]

Boring them out would require the purchase of oversized slides which are not available, to my knowledge.  You are looking at a controlled fit for the purpose of air flow and not just a hole with a sliding plug in it.  I have also never come across what you describe in rebuilding hundreds of carbs.  Maybe a picture would help?  The slides do have an alignment slot that must be lined up with a dowel or they will not close. 

[nmarshall87]

I'm going to try and upload a video so you can see what I mean. I think that will be easier to understand.

[nmarshall87]

Okay, here is a YouTube video demonstrating the problem. Let me know what you think.

[bollingball]

Ok first quit doing what your doing your just causing more damage each time. you have to figure out if its the slide or the bore try one of your other slides but don't force if it starts to hang up then you know it is the bore. put some oil on it when you do this. Maybe try a fine brake hone or fine emery cloth.inspect closely for buildup of crude or damage.

[nmarshall87]

I tried with another slide and it did also stick so it must be the bore. There doesn't appear to be anything in the bore that would be causing the slide to stick, though.

[KingCustomCycles.com]

I have come across that, sorry for the misunderstanding.  You have some varnish build-up in the bore.  I use scotch brite nylon scrubbers with lacquer thinner, MEK, or regular carb cleaner.  Wrap the pad around a wood dowel to give it some back bone.  The only other alternative is a warped or distorted bore from a crash or something.  Either way, a cleaning and polish will clear it up.  This is one case WD40 might help, it is a solvent and lubricant.  No new parts required, just polish and clean the old ones.

[nmarshall87]

Thanks for the suggestions guys, I'm gonna go try the scrubber wd40 idea before I rush out and try another set of carbs. I'll let you know what happens

[bollingball]

Well you could take it to a machine shop if you don't have the mikes and let them check for out of round or just start looking for a used bank it is allways nice to have extra parts.

[gnarlycharlie4u]

Sounds like a good plan. I agree with hitting it with some mineral spirits before anything else.

I was under the impression that they were in worse shape than they are.

Hopefully there are no gashes or scratches in there. If there are, hopefully they're not bad and some fine steel wool or emery cloth or something of the sort can fix it up.

If you have a dremel I would pick up some polishing compound and hit the slides and bores after you clean and prep them with the turpentine or lacquer thinner or whatever mineral spirit you use.

Be sure to use some more lacquer thinner to clean off the polish compound when you're done though. Then lube it up and see if it slides freely.

Well you could take it to a machine shop if you don't have the mikes and let them check for out of round or just start looking for a used bank it is allways nice to have extra parts.

This exactly. You never know when you'll need a backup and it never hurts to have an extra set of carbs lying around. I've got a collection of about 4 different sets that I'm rebuilding/have rebuilt.

I plan on having a a couple sets per motorcycle that I can just swap depending on my riding conditions (elevation, exhaust headers, etc...) instead of having to re-jet and re-tune everything every time I change conditions.