Leaking needle seat needs agressive polishing

[Matt Story]

#3 carb on my 77 cb750f has a badly corroded needle seat.  I have been through the carbs with rebuild kits needle valves included (rubber tipped), tuned the bike so it starts and idles nice.  A couple of the seats needed to be polished.  All but # 3 are sealing up nicely.  A PO had turned that float upside down in an effort to get better pressure on the valve I think.

On these carbs, the seat is not removable by screwing it out.  I am considering drastic measures to get this thing to seal up.

If I machine the seat to a deeper depth, could I just adjust the float tang to compensate?  How much deeper could I go with this methodology?  Could I get a taller needle valve to make the height difference?

I could pull the seat out by force, maybe by tapping the center and using a puller, or maybe like the idle jet, I could just pull it out with vice grips.  I could then turn a replacement seat out of brass and press it in.  This would duplicate the stock seat dimensions and would require no change to the needle or float.

I could somehow press or epoxy a new seat into the existing seat bore.  I would make it as thin as possible, but like the first option, dimensional adjustments would need to be made to the needle or float to gt the right fuel level.

Your thoughts?

Thanks

Matt

[TOOLS1]

Since the tang on the float is there for adjustment of the float height, I do not see why you could not machine the seat deeper. Also the needles out of the Suzuki GS 550 will go right into the CB carbs, and they are about 1mm longer. As to removing the seat, I have never done this, but I know they are pressed in, so taping them, and using a puller should take them right out without damaging the carb bodies.
TOOLS

[Lucky 1]

I am surprised the carbs have not been completely ruined by now.

"A couple of the seats needed to be polished." No need to polish seats. Just clean the carbs.
" A PO turned the floats upside down" Unbelievable.
"machine the seat"  How would you do that accurately?

You need to get some expert help before the carbs are completely ruined.

Do you even know the angle of that seat?

I would not remove more than .001 if at all possible, if you can find the correct tool.
Turn by hand of course!
Check to see if the seats are even available FIRST.

[Matt Story]

When the seats are causing a leak issue, and the seat shoulder/edge is irregular to the point that the unevenness can be seen with the eye, you can chose to repair or live with the leak.  I chose against living with the leak.  That makes redressing/polishing the surface necessary (and by looking around the internet, quite common).  This bike sat for some number of years non-running as so many of these bikes have.  The guy I bought the bike from never had it running.  He or (more likely) the guy he bought it from recognized the problem was with carb 3 and turned the float upside down to get more pressure on the seat.  Of course that caused other running problems as well as it didn't fix the leak issue.

2 of the other seats also had damage that have been polished and are now repaired.  So far this seat has had the same treatment if not to a higher degree.  Before going further, I wanted to know if other longer needles were available.  I don't think I'll need to take out a whole mm of material, but knowing (thanks Tools) that my needle could be replaced with a longer one opens up the options.

I will continue polishing/machining by hand more agressively to true up the sealing edge, comforted in the knowledge that, if necessary, I can get that longer needle.  Before I do that, I will measure up the seats so that I can machine a replacement if necessary.  What is already broken can only be repaired, and I am competent enough in machining and mechanics, I am sure I can fix it.  I may just fixture the carb body up on a Bridgeport, indicate the hole and machine the shoulder at speed..

[Matt Story]

It took me a while to get back to this project.

Instead of buying another used set of carbs with inknown provenance, I chose to first attempt to repair my badly corroded #3 float needle seat.  I started by making the tool above.  Both ends are turned to fit the ID of the seat.  One has. 70 degree tapered and polished point.  The other a blunt polished end.  I first ran the blunt tool at low speed and pressure in the drill for several minutes with toothpaste followed by the same treatment with the tapered end.  I reset the float level (all of thwm actually to the lowest setting to get more closing pressure.  First I tested for leaks with the carbs bolted to my bench.  I couldnt get it to leak, so I remounted them.  The bike has been started and stopped a dozen times and ran around the neighborhood.  I left the petcock open overnight intensionally.

No more leak.  Problem solved.

By the way, these non-removable seats are not pressed into a shoulder for depth.  I know because I made another atempt at repair by using my arbor as a punch to lightly upset the sealing edge.  This only pushed the seat deeper into the carb body.

Hope this is helpful to others.

Matt