Topic: float height related to low vacuum sooted plugs

[haill]

hello once again
took the carbs out tonight. once more in my quest for 1971 CB500 glory for it's been a long resto lest in my mind...  there was a leak which would happen in number 3.  drain gas all over the place then  stop and do it again some time later. Note have clean them through and boiled took out emulsifier tubes all jets etc are stock numbers as well as air box. 4into1 with uni filter.
bent the floats up till the lines that are cast in them where parallel to the casting  of the carb body which was pretty much 7/8 of an inch closed. carb model #627b
this was done in order to see if the valve seats were leaking slowly and causing the sooting of the plugs. all of them thick with soot with rich exhaust smell and poor idle and running.
this upon start up worked for sometime. one minute maybe. there was good vacuum on my carbtune. there was none before. the rich exhaust smell was gone and it idled and rev-ed happily. then quickly the vacuum disappeared, the exhaust went back to thick and full of gas and it started to idle horrible and rev with back fire.
my thinking has put me in the idea that the value seats leak, lest two of them in each rack. this raises the gas level till the carbs are drowning in gas. don't have the type of float bowl screws that allow one to put clear tubing on and check the gas level. which would be nice right now.
was thinking the compression was off. but since checking it seems to be constant across the bank and doesn't increase with addition of oil.
please point me in the direction of being able to get this bike out of my shop and riding down the road.
kind regards Keith Haill nova scotia Canada.

[TwoTired]

What float height measurement did you use? Describe how you measured it.
Were there any burrs on the float pivot pins, or on the posts at either end of the float pivot brass?
Have the orings in the carbs been renewed?  Including the ones on the float valve seats?
Did you closely examine the float valve tips and seats for roundness, burrs, or other iregularities?
Are you running on the side stand or the center stand?

If it goes into too rich mode, and you turn off the fuel tap, does it run better until the fuel runs out of the bowls?

Can you put it on the center stand?  Then fill the carb bowls, and have it running int too rich mode, stop the bike and remove each carb bowl to see the fuel quantity in each bowl?

Do any of the headpipes run at different temperatures than the others when the problem is existent?

How old is the gas you are using?

Is the fuel you are feeding to the cleaned carbs also clean?  Gas tank clean inside?  Have you checked the fuel tap sediment bowl and screen?

[haill]

Have read some of your posts you seem to be a wealth of knowledge so  appreciate your time...
the o rings have not been changed. which might be the issue. the float valves seem  to be original as do the jets etc.
the tips of the float pins look good by my eye but only gauging on whats there. clean now but used 23000 miles would think. do they wear out? or just lose the ability to seat themselves.
the spring etc works correctly.
the floats were set according to the Honda manual. then tonight bent them to lessen fuel flow so when just resting against the pin the cast mark on the float was parallel the the carb body.
the carbs have been leaking gas almost a tank full when left the petcock on one night.  thought floats where holding well. the problem with leaking starts after gas has been on for sometime 10 minutes maybe and mostly lest what i saw came out of the overflow of number three in large amounts not drips but full running of fuel.
the tank is clean used acid then oil. the fuel is new. carbs have been separated completely and boiled in brake fluid lemon juice and water each for 30 minutes. the emulsion tubes were removed as well.
only have a center stand on the bike. pipes all hot. plugs all the same soot. dry soot all over the entire surface of the plug. not damp with oil just dry with black soot. new resistor caps and plugs.
new air box rubbers installed tonight.
will try the turning off fuel and see if it clears before running out. like the idea of the o rings thou it fits for still overflowing and the float adjustment didn't cure. well if only for a minute, which was satisfying mind you...
regards from the other ocean. Keith

[Spanner 1]

The specs for your float levels is critical....needs to be ( for 627a carbs ) set at 22mm.
This measurement would be taken from the bottom of the float to the rim of the carb (upper) body with the tab on the float arm just touching the float needle valve spring with the needle lightly seated in the valve.......easiest to achieve with the carbs on the bench held sideways, i.e. float pins vertical.

[haill]

one other thing of note. though stated cleaned carbs. the float bowl overflow tubes where not checked for being open at the top. had two that were cracked and solider them closed but never checked for flow through. have drained the carb bowls many times with the drain screws. the reason  state this is though i say that number three leaks and it does. the others may need to take a leak and not drain. floating gas into the cylinders. the carbs were horrible dirty when first opened, for bike had sat on off for 15 years. will check that. thinking of getting a full carb kit for each now, but first will try a locate some o'rings for the floats valve seats and see if those and checking the tubes helps matters. any manufacture of carb kits preferred for the 71 CB500 with 627b carbs. thanks. Keith

[haill]

Thanks mister spanner.
have had them set to this measurement using the method described but changed it tonight to lessen the amount of fuel to test if the floats where not doing their job. this worked for about a minute then back to running verrrrrrrrrrry rich. twotired made a very good suggestion to o rings leaking but that would still make the floats stop fuel if set correctly.   if the float valves arn't holding out gas when shut. the combination of possible blocked overflow tubes with leaking gas flow makes me look to them for the solution.
thanks for putting your hand up. Keith

[Spanner 1]

If your bike sat for 15 yrs. it's likely you have rust problems flowing from the gas-tank and collecting at the float valve tip/seat....very common. Might have to bite-the-bullet and de-rust the gas tank, clean out the petcock and the fuel lines all the way......lots of info here, do a search like ' tank cleaning' etcetera.....also blow thru' the 4 overflow tubes would verify if clear....

[TwoTired]

the o rings have not been changed. which might be the issue.

Likely a good part of it at least.  Honda still sells a kit to replace all the orings.

the float valves seem to be original as do the jets etc.

You might want to check the jet orifices for diameter consistent with the marking. Eg a 100 jet is a 1.00mm orifice.  Did you boil the jets in acidic hot lemon juice, too?

the tips of the float pins look good by my eye but only gauging on whats there. clean now but used 23000 miles would think. do they wear out? or just lose the ability to seat themselves.

Nothing says they last forever.  But, I have float valves/seats with over 40,000 miles on them that still work as required.  They do "marry" together as a set.  So, a valve and seat should remain a matched pair, and not mixed among carbs.

the floats were set according to the Honda manual. then tonight bent them to lessen fuel flow so when just resting against the pin the cast mark on the float was parallel the the carb body.

 
The casting mark is not an alignment feature.

the carbs have been leaking gas almost a tank full when left the petcock on one night.  thought floats where holding well. the problem with leaking starts after gas has been on for sometime 10 minutes maybe and mostly lest what i saw came out of the overflow of number three in large amounts not drips but full running of fuel.

Pretty strong evidence there is a float valve closure issue. Do the floats swing freely on the pivot pins?

the tank is clean used acid then oil. the fuel is new.

Ok.  Just be aware that it takes only the tiniest particle to block a float valve open.  The valve work well with liquid, but not so good with any solid material.

carbs have been separated completely and boiled in brake fluid lemon juice and water each for 30 minutes. the emulsion tubes were removed as well.

I'm a little concerned about the hot lemon juice.  The carb bodies aren't very acid resistant.  I would examine the oring seating surfaces in the carb body for both the float valve seat, and the main jet tower for pitting where a oring may not seal against fluid flow.

You are right to attend any block stand pipes.  If the carbs are overflowing it is possible to have fuel leak into the cylinders, past the piston rings and contaminate the oil supply...not good.

You'll get it fixed, eventually.  Just keep at it and attend to the details.

Cheers,

[haill]

the carbs were boiled in a mixture of lemon juice brake fluid and water adding water as it boiled off for each carb. they where washed after in hot water and blown out with compressor then lightly sprayed with oil wiped clean and reassembled. the o rings and jets did not take the bath. they saw some carb cleaner for short while. the o rings when thinking of condition were showing signs of age.
will recheck the float seats for any dirt which would make a leak problem and blow through the carb drain bowl tubes to check that clear. reset floats to book values. was thinking of these kits to replace all the jets gaskets etc and take out some of the guess work of what works seats and leaks. Hopefully there's a pic below.
thanks keith