Replaced perished manifold boots now v high idle speed

An overflow from the overflow pipe under the carb bowl is probably just a sticky float vavle and has got stuck because the carbs have been off /upside down/ laying on their backs etc whilst the fuel film has dried. A few taps on the float bowl with a rubber mallet or screwdriver handle is normally sufficient to get things moving again. 

If your carbs are overflowing gasoline is getting into your engine as well as the airbox.  Your engine oil could be getting contaminated

Thank you. 

I’ve given the float bowl a good number of taps with both a screwdriver handle and a rubber mallet while the engine is both off and running. 

no joy. 

what else can I try? Can I remove the float bowl with the carbs in situ, or would the needles, jets, clips fall out?

I appreciate the 2 inner screws are hard to reach and perhaps replacing the O ring would be too tricky, but my experience of removing and reseating the carbs from the bike was one of necessary brute force: the air box couldn’t move back far enough to make it straightforward, despite removing its two holding bolts. 

or would perhaps a 10 mile run naturally loosen up the float valves?

please let me know your advice. 
 

You can remove the bowl nothing will fall out or it shouldn't anyway. The floats will drop down and you'll be able to see if the float valve is moving if you lift the floats up and down. 
Another reason that fuel can continually drain from the overflow is if the brass tube in the float bowl has a crack in it. Check by filling the float bowl to below the top of the tube and see if fuel passes out the overflow. If it does then that needs fixing. It should be fuel tight until the fuel level reaches the top of the tube. 
Check those things and post back results before re assembly. 

Jimbo68 wrote:

Thank you. 

 



or would perhaps a 10 mile run naturally loosen up the float valves?

please let me know your advice. 
  

I would suggest not to try and ride it anywhere let alone 10 mils !!!! that much fuel will likely either catch fire or blow back all over the rear wheel and cause you to "eat tarmac" 

Ended up removing the carbs. Much easier with the new boots. No leak in vertical overflow pipe. The behaviour of the float in the leaky carb is different from the good one: No springiness. Not exactly stiff either. It looks more worn than the good carb. I wonder where the springiness comes from. The float valve needle?the valve does appear to move open and shut in the leaky carb.curiously the flat thin part of the float that pushes the valve needle closed is bent more towards the needle than the good carb. I’ve circled it in one of my pictures. It’s not flush with the rest of the same piece.  That would suggest someone has already had this carb open due to leaks and modified the float to close the valve sooner. Im thinking some 3-1 oil for the float pin to perhaps allow the float to spring. Perhaps it’s not moving easily on the pin. what do you suggest please as next steps. I’ve posted pictures and a couple of .mov clips, which I hope you can download and open. 

Video 1

Video 2

Those carbs are a mess and need a complete disassemble and cleaning. No amount of fiddling about will see them run right until you do.

Some one totally botched the tangs on the floats, right needle stuck and frozen.
Carefully remove the floats and bent the tangs back to the same deck as the float holder surface as a new starting point.
Remove all jets, needle valves and bleeder tubes to clean the the brown rust sludge.
Also take a look into your tank and petcock fuel filter (could be clogged).
I use a bendable magnet stick to catch the rusty flakes.

 
 
 

They do need an ultra sonic clean. 
There is a spring inside the needle valve that's why the floats bounce. It would appear the spring in the one that doesn't has collapsed or the needle valve pin has stuck in the body. 
Remove the shaft holding the floats on that carb and they just lift off. Remove the needle valve and see if the pin recess's into the valve body or is stuck down inside the body. 
If it is then the floats will allow higher fuel level in the bowl. If that level is higher than the top of the overflow tube, that's your reason for the leak. 
The pin may just be sticky from dried fuel so a clean could get it to spring back out and then work correctly. 
Clean both the float shaft and float tube. It doesn't need oiling as the oil will wash off as fuel pours through the needle valve. 

To improve the movement of this right float valve in my picture, would a soak in wd40 help? It does move in and out reasonably freely but lacks the obvious springiness of the LHS valve.