I believe there's a pilot jet, needle jet, main jet, and a needle on those that could be changed out, and a pilot screw adjustment. It really shouldn't be running that lean with stock jetting, though, unless it has a high flow exhaust and/or intake... or if someone at some point jetted it for high altitude...

If it's starving out of fuel when pulling a load, though, to the point where it stutters or quits running, it makes me think that the float bowl is running dry for some reason, more than a jetting issue. Could there be something restricting fuel through the petcock? Could there be an air leak at the intake manifold?

 

I did find a loose clamp (rubber hose between the carb. and the head) some time back when it got to where it would not run at all. I tightened it up and it help quite a bit.
It only has the problem now after it heats up under a load almost like when it heats up it starts sucking air again and leaning it out.
When I took the tank off and cleaned the fuel screen I checked the fuel petcock valve and it appeared to be working fine in all positions.
I live in Tx but purchased the quad from a dealer (new) in Northern OK. I do not think that it would have been jetted for high altitude but who knows.

 

Did you notice what size main jet was in it?

When you say it still goes lean under load, what exactly is it doing?

Anyway, for a lean condition the book says:

Clogged fuel line.
Faulty float valve.
Float level too low.
Restricted fuel line (I presume they mean kinked or pinched, since they covered clogged).
Intake air leak.
Faulty Vacuum piston.
Faulty Throttle valve.

You could try squirting some aerosol oil around both ends of the intake boot while it's running. If how it's running changes, or you get a burst of blue smoke, you'd know it's still sucking air. Other than that, I guess double checking the above is about all I could think of, along with checking the pilot screw.

 

I think what has happened is when I took the spark arrester out I should have rejeted the carb. but I did not according to a motorcycle mechanic that I talked to this morning. I am going to pull the carb. and see what jet is in there. What is the stock jet and how much over should I go?

 

I think what has happened is when I took the spark arrester out I should have rejeted the carb. but I did not according to a motorcycle mechanic that I talked to this morning. I am going to pull the carb. and see what jet is in there. What is the stock jet and how much over should I go?

 

My book is for 2003's but it says 158 main, 45 pilot. My 05 Foreman says 162 main and 45 pilot.

What is it doing when it acts up?

 

Also, I don't know if removing the spark arrester would be significant enough to lean the mixture out noticeably, but you could stick it back in and try.

Dyno-jet and others make jetting kits for the Rubicon.

 

First I notice that the machine seems to be hot but the temp. light is not on. Second it looses some HP. Then is starts missing like it is starving for fuel and will die. Let it sit a few min. and it will start and run fine for a while. Granted this is not happening when pulling just itself but rather when I am pulling or hauling a load like dragging my dog trailer through a pasture. The machine is really working when this happens but the load is not too much for this machine.
My Capitan here at the fire station is a big motorcycle rider and used to work and a mechanic and stated this morning that when he put less restrictive mufflers on his bike that it ran terrible until he rejeted the carb. and now runs fine. That's what got me to thinking that this maybe what my problem is because it did not create any problems until the machine is really having to work. Normal riding conditions do not affect it at all.

 

Running lean can cause excess temps, but it wouldn't usually loose HP and die.

I really think you are running the float bowl low, rather than a lean jetting issue. IE I think when it's running on heavy load it is burning fuel faster than it will flow into the float bowl, for whatever reason.

That would explain it running fine when not towing or pulling, but when running hard the mixture would get lean as the float level got lower, until the main jet eventually sucked air and it would stall.

How about shutting the petcock off, pull the fuel hose from the carb and put it in a jar, and open the petcock. If you get a trickle instead of a rush of fuel, you would know something is going on there.

Once you hook the fuel line back up, you could turn the petcock on, open the float bowl drain and see what happens. If you get a steady flow of fuel until the carb bowl drains, and it then turns into a dribble- then the float valve isn't flowing much fuel... On the other hand, if you get a steady flow of fuel that doesn't taper off, then I'm wrong...

Just a thought...

 

my right front brake lever once had a stuck switch, and this resulted in it not running above idle... anyone with a rubicon can simulate a failed switch, pull the front brake and hit the gas, you will be amazed