Why so lean? Kohler

[Jmoney7269]

I think so. Might still be the same engine, just a name change lol

To my understanding, the kohler command commercial engines are made in USA. But the homeowner versions: courage, confidant, 7000 serries are made overseas somewhere

 

[Jmoney7269]

Yeah I didn't even know they could run with the jet screws turned in all the way

They barely do. It was hunting pretty good with no load. That's why the plugs looked brand new and they had 100hrs on them.

 

[MRC01]

I do a lot of carburetor tuning for kawasaki brute force 650-750s. I go up from 38 pilot to 40, and go up two jet sizes as well on the mains. But here is a little trick I learned tinkering with these things. I also cut off two coils of the CV spring and drill a very small hole in the metal part in the center. After it's all reassembled, you can literally start the machine cold with no choke. Also when warmed up, you can slam the throttle from idle and it doesn't bog at all. Just instant power. I have an old school mercury carb sync tool and you would not believe how unbalanced some of these engines are. Some are off over 20hg

Most likely, the extra shims that I added to the main jet needles did something similar to your cutting the spring. And yes, this engine had 4 carbs, one per cylinder, and the OEM factory synchronization of the throttle plate positions (intake vacuum) was way off. Equalizing that also made a nice improvement. CV carbs are amazing - when properly set up they are as good as fuel injection: wide open power, part throttle response, etc. The only limitation is they won't auto-adjust for altitude.

 

[Jmoney7269]

Most likely, the extra shims that I added to the main jet needles did something similar to your cutting the spring. And yes, this engine had 4 carbs, one per cylinder, and the OEM factory synchronization of the throttle plate positions (intake vacuum) was way off. Equalizing that also made a nice improvement. CV carbs are amazing - when properly set up they are as good as fuel injection: wide open power, part throttle response, etc. The only limitation is they won't auto-adjust for altitude.

Cv carbs do work well. My kz900 has race carbs on it and they for the most part work great. You cant just slam them wide open. They were a PITA at first to get tuned. I would love to get a set of FCR carbs for it, but they are high dollar.
I helped my dad build this bike in the 90s. Lots of engine work done to it. When it gets to 9k, its got a powerband like a two stroke dirtbike all the way to 13k

 

[The motor guy]

What's a cv carburetor?

 

[Lawnman23]

What's a cv carburetor?

Constant velocity.

 

[MRC01]

What's a cv carburetor?

Constant velocity.

Yes. The key feature is that it has 2 throttle plates. The primary throttle is downstream which the throttle cable actuates. The second throttle is a slide upstream from that whose "closed" position is partially open. This 2nd slide is not controlled by the rider, but lifts (opens) based on airflow/pressure through the carb throat. This prevents the temporary lean surge if you open the throttle quickly, because full throttle requires both to open, and the 2nd one opens only when there is sufficient airflow to support it.

This 2nd slide also has a tapered needle hanging down which partially obstructs the main jet. As the slide lifts, the tapered needle lifts with it, opening the jet to increase fuel flow. Shimming the needle makes its "rest/closed" position higher up, so the needle is thinner, and more fuel can flow from the jet before it lifts.

The name "constant velocity" comes from the fact that the speed of air through the carb is relatively constant. As the airflow speeds up, this creates vacuum which lifts the slide, increasing the area (enlarging the carb throat) which slows the airflow back down.

 

[Jmoney7269]

Constant velocity.

That is a decent video at best to describe how CV carbs work. The secondary throttle blade also known as a cv pod works off vacuum signal from each cylinder. The more vacuum it calls for the higher the pods raise the flat slide. These carburetors as mentioned earlier can deliver the performance and economy of efi if they are tuned right. When you watch a CV slide in action, they pulse very slightly to keep thr correct fuel mixture. Problem is that these carbs hate modern ethanol enriched fuel. It over time causes excessive wear on any o-rings and rubber parts within a carburetor. I recommend to all my customers E0 fuel also known as ethanol free premium unleaded

 

[siriusc1024]

They barely do. It was hunting pretty good with no load. That's why the plugs looked brand new and they had 100hrs on them.

That behavior is usually a clogged pilot jet. Might also explain the lean condition.