Pulled my dad's atv out of the back of the garage. Needed a new tranny chain. Hasn't been run in about 5 years. Drained the bad gas, new plug, tore apart the carb and cleaned every thing, even ran copper wire through all the holes, jets, and needles. It was a little green in the bottom of the bowl, but not too bad. Floats are good and move freely. Air box is off. Idle screw if 1 and 1/2 turns out. Pull starting has good compression. (I don't have a comp tester) Only turns over when I add starting fluid with the choke on. Revs up, by it's self, to almost red line, then dies (or i use the kill switch). Only runs for a min or two. What should I do? Ran like a champ 5 or so years ago. Could it be the CDI?

 

I'd head for crank seals.Sitting in fuel for years just eats them up.Plus install a good carb kit.Cleaning one almost never solves a carb related problem.I've seen post after post on people pulling carbs 4 or 5 times. Once is all that's needed and you can at least cross the carb off the list of problems if the fuel supply to it is ok.https://www.ebay.com/itm/Shindy-Carb...hZ8qlU&vxp=mtr https://www.ebay.com/itm/Polaris-Tra...5ZJdP7&vxp=mtr

 

If it starts up, but goes to high idle, that usually indicates a lean condition (too much air to the amount of fuel.) Stock carburetors need to have the airbox that was designed to be on that machine for the proper amount and flow of air.
You can easily verify this by starting the engine and holding a gloved hand over the open end of the carburetor to restrict a small amount of airflow. If it won't start right up, put a tablespoon of gas in the carb then start it and try restricting the air, should idle easily.
Always be very careful placing anything in carb jets that can be broken or that can enlarge the diameter of the jets.
Hope this helps!

 

so...if it "only runs on starting fluid" you have a fuel delivery issue. Which is a good thing because it narrows things down a bunch. Here are some questions & thoughts:
1) during your carb cleaning did you pull the idle (pilot) jet? It's usually seated far down next to the main jet and requires an exact fitting screw driver to remove. If that wasn't serviced I'd start there.
2) are you sure your carb bowl is getting fuel? Easy way to check that is to remove bowl and turn the fuel on...at same time you can validate your float needle functions because you can manually stop the flow of fuel by pushing up on the float.
3) engine pulse - this is what OPT was getting at with the crank seals - if you put your hand over the carb intake and crank the engine do you feel a strong pull? If not then your crank seals are pulling in air and not letting enough negative pressure to draw in air/fuel from the carb.


Check these and report back...

 

Had the same problem with my 2001 trailblazer 250 2 months ago after it sat for 8 months. 90% of the time it will be the carburetor. I cleaned mine, re-assembled and it would still only run for a moment. I did everything else, checked compression, pulled the magneto and checked the timing, and when everything else failed, I pulled the carburetor again and meticulously re-cleaned it and that fixed the problem.

 

Once and done with a good quality kit and a good cleaning. 15-16 year old carbs will have worn parts,needle and seats are a constant wear item along with slide needles,o-rings,etc. You can get a good kit for the less than the price of an oem needle and seat and it will be like a new carb again and last for years.

 

It's got good compression, I can hear it sucking in air. I just put in my new carb kit and cleaned the body again. Had to use starting fluid to start it, with the choke on. Starts, then goes into high idle, then I try to take the choke off and it winds up to almost full throttle, so i kill switch it. Going to try it with the air box ON this time. The air filter is grimmy as all hell so i think i'll leave it out for the time being, unless that also needs to be in.

 

Have you checked the condition of the carb boot and the crank seals? These 250's are pretty well known for there carb boot issues. If you have been taking the carb off and on it may cause a brittle boot to become cracked and suck air in while running. Crank seals leaking are usually the culprit of hard starting.

Mike

 

Got the airbox on, helped a little. Can now start it WITHOUT starting fluid, but with the choke on. Messing with the air mixture screw and the idol screws, I can get the idol down to where I think it should be sounding with the choke on, BUT as soon as I flip off the choke it runs up to at least half (then i got scared and shut it off). This makes no sense to me. I always thought that "choke" meant a richer mix and idol'd faster. Anyone have stock settings for the air mixture screw and the idol screw? My other one (i have 2 of these atv's) is set at 1&1/2 turns out for the idol screw and the air mixture screw was set at 1/8 out. Any other ideas? I'm stumped and mad now.

Mike: Yea i bought a brand new boot before I even started it. The old one pretty much disintegrated in my hands.


DirtDevil101: Installed a new carb kit and all the carb gaskets, The bowl is full of gas and the floats and both working. When the engine IS running it is not pulsing.

 

1-2 turns out on the air screw(rear of the carb) on average.The air screw isn't as sensitive as a pilot screw(fuel screw) on a 4 stroke carb.The idle screw is just adjusted in or out to get a steady idle.Make sure you have a little slack at the thumb throttle. Spray a little WD40 or contact cleaner around the intake manifold and base gasket area and see if the idle changes. If it does then you have an air leak. If it still idles high and if you have the carb slide in correctly,jetting correct,etc then I'd still say possible crank seals sucking air. The main culprit was usually the one behind the drive clutch.