MTFCA Forum

I have a Holley G that idles lean. It is brass with a steel bowl. If I open the adjustment a little you can get it to run pretty well at low RPMs. But accelerating and driving it’s too rich. Then you end up turning the adjustment about a quarter turn more lean and it runs great. I am not sure if it is float level or not. Is there a way of checking that while on the car. I know the idle tube has to be submerged in the puddle. Can you see that by removing the top of the carburetor? If so, how submerged does it need to be? Is that the way to adjust the idle mixture? I think I may have heard that these carburetors are a little touchy on the float level. Is that true?


Thanks in advance

Brian

I hope you get an answer to this as there are some pretty knowledgeable folks on this list who will certainly have some sound advice for you.

Paul

greenacres36 wrote: ↑

Wed Aug 25, 2021 8:41 pm

I have a Holley G that idles lean. It is brass with a steel bowl. If I open the adjustment a little you can get it to run pretty well at low RPMs. But accelerating and driving it’s too rich. Then you end up turning the adjustment about a quarter turn more lean and it runs great. I am not sure if it is float level or not. Is there a way of checking that while on the car. I know the idle tube has to be submerged in the puddle. Can you see that by removing the top of the carburetor? If so, how submerged does it need to be? Is that the way to adjust the idle mixture? I think I may have heard that these carburetors are a little touchy on the float level. Is that true?


Thanks in advance

Brian

I have done a few. The fuel level in the jet bowl is critical & the tube end. Set the float & run fuel to it with the adjusting needle cover off. Check the jet bowl. Adjust the float until correct. The specs are in the Service essentials by M Fahnestock. There are a bunch of critical specs spread out over a couple dozen pages. I am not able to dig em all out for you at this time.

1/16" deep in the jet well is a bit thin on depth. Somewhere between 1/16 and 1/8 is what you want and you're describing a very lean idle which 1/16" can give you. The pickup tube needs to be barely off the bottom of the jet well, out of the way of the adjusting needle, and the little nut that holds the tube in in place needs to be snug and the flare on the tube undamaged so that there are no air leaks.

Modern float material is more buoyant than cork and thus, you must sometimes alter the profile/volume of the float so as to act right. If it's cork, it's probably original...if it's black, it's new and may be shutting off flow from the float valve prematurely even if set "by the book".

You have to look down into the carb through the top plate to really see things. If the puddle is too deep then it will flow out the overflow tube that is hidden below the venturi and cannot be seen with it in place

Here's what i found. My book has no carb info on page 202.. The low speed tube is .011-.018 off the bottom,. Float: 1/2" from gasket surface. Fuel level in the jet bowl only mentions a special ford gauge tool. The illustration shows the fuel level centered between the bottom of the jet bowl & the top of the jet tabs. Dont see an exact dimension.
As in adjusting a NH, if when hi speed is set & idle is lean, fuel level is too low. The neat thing about the G carb is the ability to see the fuel level. With the NH its trial & error.

Thank you so much. Now I guess I have some work to do. I think the Holley G is a beautiful carburetor. I’ll pull the top and check the float level.

The MTFCA carburetor book covers the Holley "G". It's worth the trouble to set up the test fixture shown in that manual, as setting the float level and resulting "puddle" can be done much more easily on the bench with a fixture than on the car. Safer, too, if you use parts wash solvent instead of gasoline with the fixture. My experience with the "newfangled" composite float is that it is way oversized compared to the profile of the original cork, which results in its being more buoyant. Pared down to the original cork profile, buoyancy is very nearly equal to cork.

There are several posts on this site with good information on Holley G carbs. One post has a drawing of the "tool" used to measure the float level. You set the float, fill the bowl and then use the tool to check the depth of the fuel in the cup. Then, remove the bowl and repeat about a dozen times. As noted, you really need to have a fixture to avoid removing the bowl after each attempt. It didn't make sense until I tried it, so I am including a picture below.

There are many different depth recommendations, generally between 1/16" and 1/8". Fahnestock book shows 1/16". I have not seen a specific depth recommendation from Stan Howe (RIP). He did note that the pool had to cover the end of the idle tube, a car can be hard to start if the level is too low, and if too high the car will "slobber" when starting. My depth is set at about 1/8", the car runs great but does require 3-4 choke pulls when cold.

Other ideas:
Examine the idle tube closely. Mine had cracked near the bend, the car ran but not great. I soldered the crack, then later found a good replacement.
If you want a bigger project, you can remove (unscrew) the main jet cup and clean under there. There are some tiny holes that can get plugged up.

Thank you. I think I will make a fixture. It’s been mentioned a couple of times so I will take that advice. The Ohio model T jamboree is this weekend so I’m afraid to tear into it until after the jamboree. I know how sometimes you can open a can of worms and I would hate to have the car disabled. It runs great but just idles a little on the lean side but I can get through this weekend and then that will be my next project. I like your homemade gauge idea. I think I would do the same.

I failed to state that the car starts fantastic. It started on the first compression today cold. Usually starts on the second. I’m thankful for that