KZ 900 Carburator has internal leak.

The subject title should be change for KZ 900 carburator gas supply restriction. As per issue discovery !

Hi, I did a floats adjustment with clear tubes. I noticed that carburetor 3 and 4 have an internal leak. Once the fuel level has filled the bowls and the float valves are closed, the fuel line supply keep feeding the carburators for app 1 oz or the equivalent of 1-1/2 time the lenght of my fuel line supply set up.
Note: I have new float valves and seats.
Could it be a starter plunger issue ?  And could this explain the small backfire at start up ??

 

When You say keeps feeding the carbs, meaning? Is it coming thru the venturi's or spilling out?? Please elaborate. 

 

No external leak. When gas level reach the correct level inside the the bowl: (1/8'' below the top of the bowl) the float valve close: (in green) 
but the remaining gas in the fill line: (in red) will slowly continue to drain into the cabs : if full, it will drain competely and if I do a seconf fill, only 1/2 will go into the carbs. The remaning gas in the fill line will stay at same level.

That mean the floats work correctly,  but there is a leak somewhere before the float valve and the gas go somewhere in the carb  

It sounds like you may have an air bubble in the supply line, and as the bubble clears, it visually appears that the fuel is continuing to enter.  

Simple fact is that if fuel was entering the carbs, you would see it in the clear tubes.

I think I've found the problem! I connected a hose on the T and blew into it. Carb 1-2: I hear the air blown with a slight restriction.

Carb 3-4: It almost block. Air go in slowly... like the gas in that fill line.

See how the T was installed with a sealant (by previous owner) it must be a restriction not far away.

I guess I have to replace these T's and find the blockage. Any recommendation for good T's. ? 

I would say you need new tees. Someone tried to use the old ones wrapping teflon tape around them. 

Found that issue ''Carb 3-4: It almost block. Air go in slowly... like the gas in that fill line''

The restriction was caused by float # 4 being to low and touching the bottom of the bowl. It was almost closing the float valve.

Good find! Ins't working on old machines an interesting thing? One tends to have to touch, listen and exam the entire machine. Not like new equipment where a computer does that? I certainly think so but just what do I know? I know I am just old.

Thanks,  It's a chace to be old because otherwise we would have no clue to find out what's going on!
At least with old thing

But I still have an issue with carb # 4 : When the gas goes in the bowl, the clear tube stop rising at some point (valve close I guess) then slowly rise app 5 mm / 1/4''. Last time I tried, it leaked by the over flow.

A funny thing.... Maybe not!
I took the #1 carburetor float which has the old float valve and seat that work perfectly and installed it in #4 which has the new valve and Keyster seat and guess what! No gas entered the carburetor just like the previous issue with #4)

Comparing the 2 seats, they are 1 mm difference and the valve pin at the end are also longer. Enough to have this problem
Before doing the clear tube check, all floats were set at 26 mm / 1.02''

 
 

Possibly a better way to compare those valves is to position them with the shoulders in line not the ends.  Then put the respective needles in them and compare where the needle ends contact the float tangs.  That will compare the points where the needle valves shut off the fuel flow.

Keyster are 1.2 mm / 0.47'' taller.
To-do list for tomorrow: Adjust, floats accordingly!

   

Just in case someone think it's my first BB"Q 



Me at 19 yo on a brand new 75