I've got an old single cyl Kubota T1400H with a Mikuni carb that keeps over filling the bowl until it floods over. I got a new needle (with a rubber tip) and put it in- same thing. The float isn't full of fuel, and I even set the level a little lower- just to try it, but it keeps overfilling. I've got this old rig running, and this is the LAST thing I need to fix. Right now I've got a fuel shut-off valve in the line and if I keep that turned about 1/2 off it runs fine- but that's no fix! Also- the hole in the carb body where the needle tip goes looks good- maybe try to ream it out a little? Any advice? Thanks, Steve
Mikuni carb flooding
- Thread starter sdodder
- Start date
You didn't mention if you changed the fuel pump but new pumps can often operate at higher PSI
Maybe the old pump is failing? (but that usually means less fuel).
Being 30 years old have you clean the fuel tank and flushed the lines. Sometimes installing a cleaned carb on a dirty system can push debris right back into the carb even with new fuel filters.
Hard to tell once all buttoned back up and installed but sometimes the float will rub on the sides of the bowl is it's a snug fit.
Time to perform a pop-off test to see what PSI the carb is holding before letting fuel into the bowl.
The seat for the needle could also be leaking. I tend to replace the needle & seat as a pair.
The seat for the needle could also be leaking. I tend to replace the needle & seat as a pair.
100%...I go one further and for about $50 i would do a full carb kit including gaskets. I have run into a lot of needle and seat problems lately. They look good but simply need replacing along with float.
I think the newer gas is screwing up the seats quickley these days
Thanks for all the quick replies! This is a simple gravity feed setup- no fuel pump. The tank is clean. As far as I can tell the float is OK.
The new needle has a rubber tip as I mentioned, but there is no "seat" - just a hole in the casting. I was thinking of CAREFULLY using a small drill bit roughly the size of the needle tip point, and (by hand) "burnishing" the opening. Think it's worth a try?
This whole thing is just an interesting "project", so I don't want to spend a bunch of money on it-
I don't see how raising the float (instead of lowering) would help-
But I'll try it- if all else fails-
Thanks, Steve
I definitely wouldn’t go reaming out the “seat” in that carb.
Instead of just randomly bending & tweaking things for a result, I would instead perform a pop off test for starters. You’re just chasing a ghost in the dark until you know if the needle is sealing off fuel flow at all.
Instead of just randomly bending & tweaking things for a result, I would instead perform a pop off test for starters. You’re just chasing a ghost in the dark until you know if the needle is sealing off fuel flow at all.
Thanks for the advice- I'll look it over 1 more time, checking the float again just to make sure the metal hinge part isn't bent.
I'll report back- Steve
I know it is weird to hear, but having a higher float allows more contact between the float and the fuel, keeping the needle pushed up. Also, a float angled down to much can allow fuel to splash up on top of it, pushing it downward.
I just want to follow up on this, if anyone else is interested.
I re-adjusted the float level, and it solved the problem!
Thanks, Steve
No drill and burnish, too aggressive. A Q-Tip with toothpaste and your fingers is all you need to clean up the seat. Once done, hold the carb upside down and blow into the fuel inlet and confirm no air passes.
Of... the carb has a drain screw on the float bowl (and a tube nipple) you can install the carb, use a length of clear tube on the nipple, open the drain and hold the tube next to the float bowl, open the tap and see the actual fuel level. it should be at or a smidge below the rim of the float bowl.
Just wanted to finish up this thread- I took it apart AGAIN and found that the float metal "hinge" was just slightly bent. I carefully straightened it, put everything back together- and IT WORKS! Thanks for all the replies and suggestions. Maybe I'll figure out how to post some pics when it all done- Thanks, Steve
FYI, most float specs (if you do not have an actual measurement to use) is the have the float parallel to the carb gasket surface when upside down. If... the float needle has a spring loaded 'pin', then its a bit more of a PITA, you have to hold the carb at about 45 degrees, the goal being to not fully depress the pin, but just a tiny bit, enough to close the needle valve. The pins being spring loaded to to aid it closing the valve in rough use.
But, it sounds like you have it sorted out,so KUDOS!
