In this article I explained how I adjusted the carbs to correct a running rich condition.


Adjusting the carbs that way worked for a period of time of roughly 3-4 hours before it started to really struggle under load (when pulling a lot of dirt or operating many of the cylinders at once.)  This condition has happened before and so it wasn’t entirely surprising.  However rarely before did I think about what might be causing this.  This time, being acutely aware of how I affected the carb with my adjustments, I thought perhaps what I had done to “fix” the problem wasn’t in fact a true fix.

Here are the factors involved as I understood them then.

  • Fuel level in the bowl
  • Amount of fuel entering the intake manifold
  • Amount of air entering the intake manifold

These factors I attempted to adjust by bending the floats so they shut the fuel off faster and allowed less fuel to slip in the venturi.  Well, I did manage to do this, but I created the problem of reducing the total amount of fuel available for load conditions.  It’s worth noting that I filled the fuel tank a couple of times during this run well / run poorly phase.


In my “spare” time I continued my hunt to find the type of carb that was in this machine.  In the last article you’ll see that I found a website with a picture of the exact carb, which showed it was a zenith 33.  Well I found further down a video of it, in which, they did a walk through of the carb.  At the end of this video I noticed three cups they showed next to the carb.  I identified these as venturis and they were all different sizes. My first inclination was that perhaps this IS the correct carb, but the wrong venturi.  So I contacted the website and asked them if they sold different venturis and what they were for.

Zenith 33 Carb number

Well someone got back to me right away and we chatted about my problems with the carb and the venturis and we left it at, I would get the number off the carb and also the number of the venturi. zenith carb venturi number 24 He suggested just shining a light down the carb and i’d see the number on the venturi.  Unfortunately the position of the carb makes it hard to do this.  I was also at the point where I knew I should probably undo the bending that I had done previously.  And so The carb had to come out anyway.


Disassemble 2

I pulled the carb out, and took it apart.  I was getting good at it at this point.  I could probably write a tutorial on it.  It would go something like this.

  • Grab Tools – 1/2 Inch wrench, standard screwdriver, linemans pliers
  • from left of machine remove idler/governer rod
  • from right side of machine right foot on steering tierod and left foot on rear tire
  • Open middle top cover
  • loosen hose clamp on intake boot, push out of way
  • use 1/2 inch wrench to remove 2 nuts off intake manifold studs that hold carb on
  • leave nuts at the top of stud until both are 1/2 turn away from coming off
  • lift carb up 1/2 inch and remove the nuts the rest of the way (they can’t come otherwise)
  • turn carb around and remove choke cable
  • use plier to pinch clamp and slide down fuel line, remove
  • remove carb and bring back to multi thousand dollar workshop (or in my case two buckets)  Garage Justification #354

workshop - two buckets

So I cleaned the carb a bit while i was in there.  I seem to always be short on small brushes when i need to clean a carb.  Of course i’ve already remember this while at a store and also purchased a bag of small brushes exactly for this purchase but I have no idea what box they got stuck in…sigh.  (Garage Justification #123)  I actually clean a bunch of crud out and so I was hopeful that this would improve things.  I also bent the carbs back hopefully the same amount that i bent them in the first place.  They sit in a slot in the carb and are also relatively sloppy which makes it hard to really measure the float level (distance from floats to top of bowl)  So I guessed.

Reassembled the carb and stuck it back on.  And again.  It Ran!  Another miracle.  At first the engine took off.  Revving and Revving up and up and up to an rpm which i’ve never heard from that engine before but it sounded amazing and strong and i quickly hopped into the backhoe seat and started digging at breakneck speed. It was incredible i could use multiple rams at the same time and swing and lift and dump and curl.  For a short time I was making sure that I did at least two which kept the RPM’s down to a normal level, for if I stopped for a second they started to climb. It was kind of strange, so I killed the throttle and noticed nothing changed.  What?  so I shut the key off and at that second it hit me that I forgot to reconnect the governor!!

…and for a second our hero calculated his ability to run the backhoe in such a way as to manage the rpm’s but also get as much work done as possible and no one would be the wiser.  however soon the feeling doubt crept in, and infected the genius with images of an exploding engine and towing the backhoe out of the hole.  Lucky for him it’s thoughts like this that go as quickly as they come…

So I hopped down and connected the rod, hopped back on, and away I dug.  I used the backhoe for the next hour without incident.


During this process (I was digging a foundation) I moved the backhoe a lot however until this point i’d kept it oriented one way on the hill facing down.  As I started to exit the hole I was facing up hill and the backhoe started to act up again.  It did the same lean condition that I thought i’d just fixed.   (semi-frustrated at this point)  I didn’t have a choice because I needed this foundation dug and so I muscled through the condition until I was finished.  Just waiting for the engine to catch up when it started to die.  Also tried running with the choke on, or pulling it out just as it hit a lean condition.

List of Factors Involved:

  • Fuel level in the bowl
  • Amount of fuel entering the intake manifold
  • Amount of air entering the intake manifold
  • Orientation in relation to the ground



Running Lean
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