Carburetor Adjustments... Float and Main Metering Jet

Mon Dec 29, 2003 9:15 pm

I would like to get some advice on adjustments to the carburetor which I just recently re-built. It is the IH carburetor.

First, the main metering jet. I am not really sure how far it should be screwed in. Where should the holes be located when it is correctly installed?

Second, the float. I thought I was getting too much gas, and so bent the float up, ie so that it shuts off sooner? (correct, right?). Now, thinking about it, I wonder if I have it shutting off later, and there is too much gas.

Anyway, there is about less than 1/16" movement of the needle valve (ie when there is no gas in the chamber, there is about an 1/8" of the bottom of the needle valve showing, and then when the float activates, there is about 1/16" showing. Is this correct? My friend said that it should be level - but level with what? All I can see, is that when the float is in it's lowest position, then maybe the top should be level with the bottom of the venturi (right now, the top is about 1/8" higher than the bottom of the venturi), and when the float is "floating" at its highest point, the top is about 1/8" below the bottom of the flange of the case. Is this correct?

Finally, the throttle butterfly. If you are looking the carburetor as though it is attached to the engine, the butterfly is pointed down to the right, and up to the left? Is this correct?

Anyhelp would be appreciated. Thanks

Mon Dec 29, 2003 9:38 pm


Without going into a long winded explanation, suffice to say that your answers are contained here:

On the main Forum page, there is a sticky - New Members and Visitors Please Read --

In that sticky you will find links to "The Best of H.L. Chauvin", The Cub Manual Server (here I would check the Blue Ribbon Service Manuals, as well as to the ATIS FAQ's.

The best possible answer is for you to read those articles. Based on experience here as a relative newbie - I had to read H.L.'s articles a number of times and consult the Blue Ribbons as well to get it all together. Also, you might want to look at the Parts Manuals - expecially the TC-37A, which has good blowups of the carb itself.

I would recommend that you make the little gadget that H.L. recommends to adjust the float - it really works - usually first time!

Hope this helps a bit.

Mon Dec 29, 2003 10:08 pm

Thanks for the help. I feel a little stupid because just after I made that post, I read the HL Chauvin article, which I think you referred to. The piece I have read abour 10 times now, but I can't understand is:

"but, first turn carburetor upside down to insure that the metal float tang is dead level with the joint between the upper and lower half when it touches and seats the needle valve".

Can you explain this one more time, in a little different way? "Dead level" ... does that mean parallel to?

Tomorrow I will buy the 1/8" plug, tube etc, because that seems like a great way to get it set correctly.

I guess the setting of the main metering valve is in the Blue Ribbon manual (which by the way, is not able to be retrieved (the link doesn't work).

Thanks again

Mon Dec 29, 2003 10:11 pm


Just to clarify, this is the link that doesn't work: ... index.html


Mon Dec 29, 2003 10:49 pm

I didn't go back and look at the article, but I believe it is saying the tab should be parallel to the joint.

The main jet screws clear in to where the shoulder bottoms on the side of the housing. There should be a gasket there. It doesn't matter which way the side holes face.

Rudi has been moving things around. Try going in from the index. Or this should get you there:

Mon Dec 29, 2003 11:51 pm


You wrote:

"but, first turn carburetor upside down to insure that the metal float tang is dead level with the joint between the upper and lower half when it touches and seats the needle valve".

Can you explain this one more time, in a little different way? "Dead level" ... does that mean parallel to?

That is exactly how I understood it, and I proceeded from that point on. You should have no trouble. The tang is the little tab at the back of the float.

Oh, fixed the broken link, the boo-boo on the index for page 20 and the return to previous button. The whole manual should work now.

As Jim said, been moving things around, doing a little housekeeping and a few things get overlooked.

If anyone finds a broken link, please let me know ASAP.... thanks

Tue Dec 30, 2003 9:03 pm

Thanks Rudi.

I followed the directions in the HL Chauvin article, and also in GSS1411, which I looked at today, and now the Cub runs really nice!

One question though, when you put the tube on the bottom of the carb, and measure the level, I did this first when it wasn't running, and then adjusted the float accordingly. When I put it back on, the level was right at 5/8", so I fgured it was good. Then I started the tractor, and ran it a several power settings. At high power settings, the level dropped, so that the 5/8" increased to about 1". Is this normal? Or do I still not have enough level?

Tue Dec 30, 2003 9:09 pm


I followed the same instructions from H.L., and did the adjustments with Ellie not running. I have not done the measurements you have with Ellie running, so I have no basis for comparison. I figured ifn she run real good with that setting then that must be the one. I am not one to tempt the gremlins more than I have to :!: :lol:

Jim might be the better one to answer this question.

Glad you got your Cub running right and the info helped.

Tue Dec 30, 2003 9:45 pm

I never tried measuring that either. But I'll throw out a couple observations anyway.

1) If the tractor runs OK, I wouldn't worry about it.

2) That seems like a lot of drop to me. The float drop on that carburetor is only supposed to be 3/16. So you are going to get the maximum flow into the bowl as soon as the level drops by 3/16. If fuel level drops more than that, it means fuel is being pulled out faster than it can flow in. I would expect the engine to starve out if run this way for a period of time.

When you had the carburetor apart, did you make sure the float was adjusted to get the full 3/16 float drop?

Tue Dec 30, 2003 10:22 pm


Yes I checked to make sure I got that drop, in fact, in order to get the level correct, it dropped a little more than 3/16, closer to 1/4" or 5/16".