Setting Float Height on Carb

Fri Apr 01, 2005 1:03 am

Reading through many recent posts discussing over rich carb's, I see I'm in good company. My Cub has run rich since I bought it, despite mixture adjustment, hotter plugs, cleaned air cleaner, float seems dry, etc. I recently rebuilt the carb (IH kit) to no avail. It carboned up the plugs in less than an hour's operation. It also drips gas from the drip port on the carb (for lack of a better term)

The other day I followed Lurker Carl's procedure for setting the float height, but I haven't started it up to see if I did any good yet.

Here's my question.

Initial Condition:
Float Height = 1.34
Float Level = 1.57
Gas Level = 0.53

OK, gas level is on the low side (spec is 0.563-0.625) - so maybe cause of running rich - I'll try increasing float height

Adjusted Condition
Float height = 1.46
Float Level = 1.65
Gas Level = 0.75

Conclusion: Now the gas level is past the spec. I'm surprised it is that sensitive: I increased Float Height 1/8", resulting in a 1/4" decrease in gas level. Is it the experience of those who have done this procedure that it is that sensitive? Maybe I went too far, but I thought I'd try it like this first and see if it runs leaner and doesn't leak gas from the carb.

I'd appreciate any thoughts and experience. Thanks

Paul

Fri Apr 01, 2005 8:58 am

The float height measurement determines the fuel level inside the bowl. The float drop measurement keeps the float from touching the bottom of the bowl, so make sure the float drop isn't too much.

The float is not a precision instrument, it's a tiny version of a toilet tank shut-off valve. Changing the float level will not correspond exactly with the change in fuel level inside the bowl. I also discovered the fuel level may be a little different each time you measure it - even without doing anything to the carburetor other than draining the bowl to take a new measurement. So measure it several times and see what the average is.

My biggest concern with trying to get the fuel level correct inside the carburetor was to stop the carburetor from draining the gas tank every time I forgot to shut off the fuel at the tank. I figured if I fixed all the leaks inside the carburetor, the fuel drain-down would stop. It worked and the tractor ran better. The key component was replacing the stock needle and cage with the Kohler brand because the Kohler needle is lighter.

Fri Apr 01, 2005 10:42 am

I think the Kohler needle is the key. Put them in both of my cubs. No leaks since but I still cut the fuel off. Thanks to Lurker Carl for that bit of info.

Fri Apr 01, 2005 5:04 pm

Got a part number and source for that Kholer needle?

Fri Apr 01, 2005 5:52 pm

I got it from my local lawnmower repair shop, you can put the part number in Google and find an internet supplier. Call the supplier and make sure it's the genuine Kohler kit, not a cheap imitation brand. You will only use the float needle, cage and gasket out of the kit. Here's the info directly from the bag:

KOHLER Genuine Part

25 757 02-S

Kit, Carburetor repair

Fri Apr 01, 2005 7:34 pm

Thanks, LC!

Fri Apr 01, 2005 9:48 pm

The float is not a precision instrument, it's a tiny version of a toilet tank shut-off valve. Changing the float level will not correspond exactly with the change in fuel level inside the bowl. I also discovered the fuel level may be a little different each time you measure it - even without doing anything to the carburetor other than draining the bowl to take a new measurement. So measure it several times and see what the average is.


Hmmmmm! :? Seems a couple of months ago I tried to convince others that this bowl level thing wasn't the rocket science some believed it to be. My own in house testing showed how much of a desparety the actual level can be espescially if you check it while the engine is running. I really think I've solved the rich running issue and I'll explain in a separate post.