Carburettors for K Series

[andrewLL 30]

Hi, is there someone that could run through a K Series carb and explain what all the bits do and how the air and fuel flow through it. Is there a cut away drawing showing what is what? When you look closely they are a bit more complex than they first appear with some very small holes which I assume are what get blocked and cause problems.

 

I have two to rebuild and two new ‘Chinese’ replacements.  I have been running a Chinese one for about seven  years now without any problems, I know some of you aren’t very impressed with them.

 

I have marked the holes in the main casting that I have found so far.  There is a large hole at the bottom on the front where on occasions a little fuel has leaked out of (blue arrow). There is then a larger hole on the right (red arrow) and a small hole at the start of the venturi (yellow arrow).  On the engine side of the carb there is a row of three tiny holes with another above them.  The needle is hollow with a two small holes at the bottom, then four in the middle and four more at the top between two threaded sections. I notice that the Chinese carb that I am using only has one hole at the bottom and it works ok.

 

hoping some one can explain, thanks, Andrew. 

[ri702bill 11,131]

Good info on carbs in the Kohler K Series Manual...

 

KohlerKseriesManual.pdf

[WHX?? 54,387]

Big Unit @ebinmaine ain't too shabby with oem carbs. 

[AlexR 2,454]

For your original carbs, get the genuine rebuild kit from Kohler it's available on Amazon among other places just know that if it's a newer production it will have Rehlko on it I thought I got ripped off for minute until I realized that is Kohlers new name haha

 

KOHLER 25 757 01-S

 

Second is try to move the throttle shaft side to side all the way around and see how much play is there, if it's too loose you will need to install some bushings. This is not a option if you want a good running engine. 

 

Hillman Group 58087 Thrust Bearing, Bronze 1/4 X 7/16 X 1/16

You will need two of these as you will have to stack 2 on top of each other. 

 

If you are lucky you will have a removable ball stud assembly on the throttle shaft that you can remove to get the bushings in. If not you will have to remove the throttle plate. The brass screws on there are peened on the back side so you may have to grind away part of the screw with a Dremel prior to trying to remove them. I have been able to remove them without doing that, but its always a risk. 

Replacement screw size is #3-48 x 1/4"

DO NOT reuse the original screws. 

You can either get brass screws again and peen them or get stainless screws with lock washer's and loctite. 

 

 

 

[Sparky-(Admin) 24,514]

On 1/31/2026 at 7:29 PM, AlexR said:

For your original carbs, get the genuine rebuild kit from Kohler it's available on Amazon among other places just know that if it's a newer production it will have Rehlko on it I thought I got ripped off for minute until I realized that is Kohlers new name haha

 

  Interesting…they just scrambled up the letters in KOHLER and settled on REHLKO? 

[AlexR 2,454]

3 hours ago, Sparky said:

Interesting…they just scrambled up the letters in KOHLER and settled on REHLKO? 

Yep that's what it looks like, I guess platinum equity bought out the engine division of Kohler and then scrambled the letters and the rest of the Kohler brand is staying the same (bath and kitchen) 

What I hope doesn't happen is because of that they stop producing parts for our old engines at some point. 

[Gasaholic 351]

On 1/31/2026 at 2:18 PM, andrewLL said:

Hi, is there someone that could run through a K Series carb and explain what all the bits do and how the air and fuel flow through it. Is there a cut away drawing showing what is what? When you look closely they are a bit more complex than they first appear with some very small holes which I assume are what get blocked and cause problems.

 

I have two to rebuild and two new ‘Chinese’ replacements.  I have been running a Chinese one for about seven  years now without any problems, I know some of you aren’t very impressed with them.

 

I have marked the holes in the main casting that I have found so far.  There is a large hole at the bottom on the front where on occasions a little fuel has leaked out of (blue arrow). There is then a larger hole on the right (red arrow) and a small hole at the start of the venturi (yellow arrow).  On the engine side of the carb there is a row of three tiny holes with another above them.  The needle is hollow with a two small holes at the bottom, then four in the middle and four more at the top between two threaded sections. I notice that the Chinese carb that I am using only has one hole at the bottom and it works ok.

 

hoping some one can explain, thanks, Andrew. 

 

Picture #1 - Blue arrow is the fuel bowl vent. This allows atmospheric pressure to act on the fuel level in the bowl (filtered air) , without it the carburetor can't work as it becomes vapor locked and cant draw fuel through the main fuel pickup. (the long needle through the middle)   That bowl vent can leak fuel or seep a bit as fuel vapor can condense in that area typically as a hot engine is cooling down... and can leak as fuel sloshes around in the bowl, or the float needle leaks, etc. 

   Yellow arrow is the idle air bleed that allows air and fuel to mix in the idle mixing chamber before being pulled into the intake side As is the red arrow (which is in play when the choke is closed mainly) 

 

Picture #2 is the idle ports set - They are in a series of ports that are controlled by the position of the throttle plate - at idle (and high idle/ top no load) the majority of fuel is coming through these little jets - as the throttle opens , more jets are uncovered allowing more fuel/air to get to the engine (Idle transition ports) until carburetor can start drawing fuel through the main jet at the middle. 

 

The various holes in the combination main jet/ emulsion tube actually pick up fuel and distribute it through more holes to feed the idle circuit and provide fuel through main jet (the holes help to break up and atomize the fuel as it is drawn through main jet at higher speeds and under load)  

 

Simplistic explanation without having a cutaway to explain the fuel flow (Kohler manual doesn't detail those very well for the Carter carb version you have pictured, but does better with explaining the Walbro version, which has a lot of similarities, just in different places) 

 

If you understand first how air is flowing through the carb it becomes easier to envision what is going on with fuel flow through the ports and passages - when throttle is mostly closed, the air flow through the main venturi is not enough to pull fuel through main jet , so the throttle plate gap over the idle jets becomes the venturi , in effect...  once throttle opens further, air flow through venturi does the lion's share of duty... 

[andrewLL 30]

Thanks Gasaholic, your explanation is just what I needed. I like to know how things work, which helps if they stop working.  And thanks to every one else that commented.  Andrew.