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Sportsman 700 carb cutting out under load


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Hey guys, figure you guys would have some helpful direction or answers.

So, 05 Sportsman 700 carb, new carb, fuel pump, new plugs, new air filter, new everything I can think of that is usually the running issues. Starts up fine, seems to run fine, but if under load, two people, or even one person, up a hill, or pulling a drag chain for the driveway, it starts to cut out and sputters and loses all power, until I back off on the throttle and just barely try to let itself catch itself and then I can take off again.

I am going crazy trying to figure this thing out. Other than that, the quad runs great. Parents bought bran new, just used around the property, 5000 miles on it. Any ideas???

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I have one that did almost the same thing. I noticed that it ran better in warm weather and really bad it cold weather.  It ran better with the choke on part way.  If I could get it running fast it ran better.  I replaced the pilot jet with one 3 sizes bigger. If it is affected by temperature it is most likely fuel related and most common is too small a jet. I also bought a new carb.  ended up with the old carb and bigger jet.

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I bought a new carb thinking it was the problem, wasn't. But I kept the original carb, and it looked great inside, so I just put the original carb back on. Whole electrical system has been replaced. I am just baffled. It seems like a fuel problem. But I can't seem to figure it out. 

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The type of day doesn't seem to matter. That is what is weird. I even took it to a shop and they found a cracked intake, which they replaced, and I thought things were good. But a little bit later, it did the same thing. The funny thing is, I KNOW it is something stupid simple that is causing the problem I just can't seem to find it. 

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Ok lets go through some steps and do a process of elimination thing.   

If your concerned or think its the carburetor then go through the manual, check the spec on the jets and the sizes and make sure everything is proper according to the specifications including the float height. Check the choke and make sure its not getting hung up or pulled in while the throttle is reving ? This way you will rule out the carburetor.  
Next would be fuel flow from the tank. Could be restricted or have some sort of vapor lock from the gas cap? Leave the cap off and see if it still gives you a problem  

After that i would look at the intake boot that connects the carburetor to engine and check for any cracks that may be sucking in air from time to time.    A simple trick to test this is spray some carburetor cleaner around the carburetor while the engine is running  and listen for any changes in the way the engine runs, lightly wiggle the carburetor as well to expose any cracks on the boot    

So after all this is done you will have ruled out any carburetor and fuel delivery issues.  

If that has not fixed the problem  i would buy an in line spark tester and attach it to the spark plug and spark plug wire and see if the spark breaks down under a throttle load.  Its about $10 bucks on Amazon.   

Get a tester and start to check the specs  on all of the electrical equipment, regulator, stator etc.  Even if you replaced them or tested to it again.   Rule out all items electrically and write down  everything.  
 

While the engine is running start wiggling the wire harness around and again listen for changes. 

After that the only thing it could be is tye cdi$$$$$$$$$ And that sucks!!!
 
 

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so engines need spark, gas, air, and compression to run.  if you can eliminate these as possibilities one at a time, you will definitely find your issue.  always start by taking a step back and thinking about what all engines need general.  this will help you not to pull your hair out and be able to logically go about the process of elimination like@Frank Angerano said

spark is the easiest to check.  (an inline spark tester will do the trick as@Frank Angerano also said)

gas is tricky as theres a lot more factors to cover.  check things in order as you "follow the gas" from the point of entry into the tank all the way to the motors top end.  (check that the breather line on the top of your tank is not plugged causing a vacuum, check the fuel valve, drain all your gas lines and blow through them to ensure they are not clogged, check your fuel pump for clogs.  i had an 04 sportsman 500 that got a clog in the fuel pump and wouldn't run right.  then check the carb as @Frank Angerano said)

air is fairly simple  check that there are no clogs before the carb, and no leaks between the carb and the motor.  (check that your air filter is clean, properly attached to the duct and that the duct is attached to the carb.  then it looks as if you've already ruled out the duct from the carb to the motor..but check it as @Frank Angerano mentioned) also, what elevation are you at?  if youre up in the mountains, then your atv will need more air than normal to run or else it will run rich (bogs on acceleration or under load)

compression.  sometimes low compression will let your atv run but doesnt have the power to pull a load. (a compression tester can be found at your local auto parts store and is usually fairly cheap)

also when did this issue start happening?  just one morning you cranked it up and boom, its not running right?  or did it come on slowly?

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Hey guys, thank you for the info and some direction to run through. I really appreciate your time and advice. I will run through your check lists and will let you know what I come up with. Like I said before, it is going to be something stupid, I hope. By the way, I replaced all the electrical in the machine, even the cdi. I will have to check compression. It has 5000+ miles on it. Does the compression go bad at any particular mileage?

Anyway, I will let you know what I find and again, thanks guys. 

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