This is going to be somewhat of a longer post, so thank you in advance for your help.

My machine: 2013 Arctic Cat 400 Core

Symptoms: ONLY WHEN HOT, not warm, HOT, it spits and sputters real bad like its either starving for fuel, or spark is intermittent. It will idle with no problems, and even up to almost 1/2 throttle, it runs pretty good. Anything past about 1/2 throttle when the bike is hot, it will spit and sputter. It also starts without an issue at all. I also might add that when starting from a cold engine, it starts easy, and idles just fine until the enricher turns off, then it will gradually idle down to a stall. I have to restart it and warm up the engine for about 2 minutes before it will idle on its own from a cold start.

I live in Naples, FL so its pretty hot in the summer time. I can ride for about an hour before it begins acting up and spits and sputters and hesitates. In the winter, when its 60 degrees or so, the problem does not happen. I also need to mention that the temperature light NEVER has come on so i don't think it is overheating.

MY ATTEMPTS TO FIX.
I've cleaned the carb multiple times and even installed a size 117 main jet, up from a 112 main jet as it has a UNI filter. I changed the fuel lines and petcock, and also wrapped the fuel lines in heat shield as I thought it was vapor lock. I replaced the vent line as well. I tried seafoam multiple times, and even tried marvel mystery oil. I've cleaned the oil cooler spotless. I checked the valve lash and everything is within spec. I began thinking it was electrical as nothing with fuel was fixing the problem. So, I changed out the coil, coil wire, plug wire, and plug - did not fix the problem. I then moved the CDI AND the voltage regulator out of the "hot zone" above the oil cooler. I put them in a place that does not get hot, and gets plenty of cool air. Issue still happens after all these tries. So last night, i began diagnosing again. I let the bike sit and idle for about 30 minutes (this allows it to get hot enough for the spitting and sputtering to happen). I then try cooling parts down with water 1 by 1 to see if i can get the bike to run better. I sprayed down the CDI, voltage regulator, oil cooler, and coil each one at a time and the problem still remained. I pulled the fuel line off the carb and it flows with no issue. I also ran the bike with the fuel petcock off to see if the carb was starving for fuel, but it wasn't as i could still ride the bike for more than a mile until the carb bowl was empty.

The last thing I did was take a hose with cold water and sprayed it directly on the carb for about 5 seconds with the bike running. I hop on the bike to test for sputtering, AND BOOM - NO SPITTING OR SPUTTERING. I was amazed.

This leaves me with two theories, and I'm hoping someone here can help me. Theory 1: Something internal on the carb is affected by the amount of heat causing it to make the bike starve for fuel. Theory 2: The water also got on the motor above the stator and cooled the stator just enough to make the spark strong again. So my theories either say the stator could be bad, or the carb has something wrong internally when exposed to heat.

I hope I was clear with my explanations. I'll take ANY advice at this point.

Thanks in advance guys.

 

Ok, I'm a Cat guy, but I'm from Maine, so bare with me, or is it bear with me? Anyway, the only Polaris that I ever owned did the same thing. However, after an hour of riding it would run like crap , set fire to itself and try to kill the rider! After trying everything, I gutted out the muffler. Supposedly it only had 1,100 miles, but he muffler/flame arrestor was plugged solid! Once I did that, it ran so good, I sold it and put the money towards an Arctic Cat 400 , which has been a great ATV. So, if you haven't, try cleaning the flame arrestor, maybe you can figure out how to ride without it. Hey, if you set fire to Florida, you can always move to Georgia.

 

Thank you for the input. I forgot to put in my explanation that I did clean out the baffle/spark arrestor with no improvement.
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Thank you for the input. I forgot to mention that I did clean the baffle/spark arrestor. LOL at the Georgia comment.

 

It came to my mind, that, next step= You need to design a water sprayer. A junkyard windshield sprayer could probably be monkey rigged. Could even rig a nozzle to spray the operator when you start to get overheated, hehe. Probably mix the water with some Odor Ban so you will smell nice for the ladies after a hard day of mudding. Heck, Arctic Cat sells a large sprayer that mounts on a rack, a squirt for the carburetor, a nice cool shower for the driver. Darn, how do I get this to "The Shark Tank"?

 

Just for grins and giggles have you sprayed the carb intake manifold with penetrant like WD40,Liquid Wrench,etc? Could be a boot cracked under the carb clamp sucking air or if like some I've found the manifold could warp,lose it's seal at the head and suck air when really hot and spit and spudder. If it is leaking you'd know real quick if the engine runs better plus you could smell the burnt penetrant through the exhaust.

 

OPT, to the rescue. Why, I didn't think of the cracked boot, duh. My 2002 AC 400 had a crack in the boot between the carburetor and air box. My mechanic warned me to check that out, as it's common.

 

Gentlemen - All efforts here are appreciated! And hydrex, your humor was especially appreciated! I believe I've fixed the issue!

The CVK-34mm carb on this bike has a fuel screw that isn't adjustable without a special tool, so I've never messed with it. Well, last night i turned the fuel screw out 1 full turn, and also adjusted the float height as i think it was a little too low creating fuel starvation. It seemed to have solved the issue as my bike started easy, and idled solid from a cold start and did not stall. It also ran WAY cooler than it did previously. In the end, not matter what your local mechanic says, if you put a UNI filter in, you must make adjustments in the carb, lesson learned. I feel dumb. For as many times as I cleaned the carb, I never adjusted the float height. And I never thought about the fuel screw because I was told that wasn't the problem as it would idle already.

 

Float height,fuel screw adjustment can play the devil with you if off. Once you get it warmed up if you have a carb pilot screw adjuster or a small screw driver and access to the screw, you can fine tune engine idle and throttle response even further. Uni is a good filter as well as filters such as Twin Air.Some may run ok on stock settings,some no.

 

I have an EZ - Adjust pms screw on mine. We change the setting in winter, maybe 1/2 turn. You might find that you need to slightly tweak it when it gets cooler, if it gets cooler in Florida, haha. I have a friend in Florida who calls me every day, asks the temperature. Today was a nice balmy 66F . Here in Maine.