I bought a used arctic cat 2003 90cc 2 stroke 4 wheeleer for my son. it had 1 year old fuel in it so I replaced spark plug and cleaned carbuerator. I drained and repaced fuel. Igot it started with starter fluid and road it for an hour but i have to keep throttle open to keep running. When I let off throttle it dies. I've messed with the fuel and air adjust screws on carb but no joy. Does anyone have any pointers on what i can do to fix this problem before my kids birthday in ten days?

Based on the information you have provided, there are a few possible causes for the issues with your 2011 Arctic Cat 550 EFI. Here are some suggestions for troubleshooting:

Check the fuel injectors: If the fuel injectors are clogged or dirty, it can cause issues with starting and idling. You may need to clean or replace the fuel injectors.

Check the fuel pressure regulator: If the fuel pressure regulator is not functioning properly, it can cause issues with fuel delivery to the engine. You may need to replace the fuel pressure regulator.

Check the air intake and filter: If the air intake or filter is dirty or clogged, it can cause issues with fuel delivery and combustion. You may need to clean or replace the air filter.

Check the throttle body: If the throttle body is dirty or clogged, it can cause issues with fuel delivery and combustion. You may need to clean the throttle body.

Check the ignition system: If the ignition system is faulty, it can cause issues with starting and idling. You may need to replace the spark plugs or coil.

Check the battery: If the battery is weak or not providing sufficient power, it can cause issues with starting and idling. You may need to replace the battery.

It's important to note that these are just suggestions based on the information you have provided..

If you've got decent compression, spark and fuel and it wont run - what about about air? Clean / new air filter installed? All 4 are needed to run.

You DROWNED it? Meaning you ran it into water so deep that it killed the motor? Chances are very good that you've done some very serious damage to that engine. Water doesn't compress, so you may have destroyed a piston or cracked the head.

Additionally, water - particularly if that water wasn't exceptionally clean (like distilled water) - will have done anything electronic no good at all, and chances are excellent that it's gotten into every gearbox on the machine.

Last and least, it may have gotten into your fuel tank. At least THAT's easy to drain & refill & add Heet to.

change the plug and make sure you are getting a good spark.

Replace the fuel filter, fuel lines, primer button (if equipped), and disassemble the carburetor, clean, and re-kit. Jet needles are preset at 1-1/2 turns CCW from stops (lightly). Make sure the spark plug fires a snappy blue spark when pulled through. If nothing, ignition parts prices and availability may justify replacing the saw with a new one. If sparks ok, start the engine and let warm up. Open the throttle and adjust H needle CW till the engine speeds up, but still 4-strokes. Proper setting is when the engine will 4-stroke, but immediately 2-stroke when cutting. Let the engine idle and adjust L CW so that the engine idles fairly well, but allows the engine to 'follow the throttle' Hope this helps!

1983-1985 Yamaha IT250K.
You need several things to get it to start: A clean carbuerator, a good reed cage, a good, clean spark plug, and compression.

Start by pulling the spark plug. If it's oily/dirty, replace it. Then kick the engine over, and you should get the motor to turn over really easy. Place the plug back into the hole, and the effort to turn the engine over should be hard, if there is compression. If there is no compression, you need to remove the cylinder head to find out why. It could be a hole in the piston, bad rings, or worse, bad crank seals. If the piston looks okay, then chances are the problem lies in the Mikuni carbuerator. It's an simple device, but you need to make sure the needle seals the bowl when the float level is correct. You also need to make sure your air enrichment circuits are free of dirt and varnish. Give it a good scrubbing. Once the carb is clean, and the float level is sound, make sure to check the air filter to ensure it is clean. The carb ensures fuel is correct. Lastly, there is spark. Your plug wire shouldn't have any cracks, and when you crank it over, there should be a spark from the plug. There is a remote chance that the pickup coil has burned out, but the ignition system on these old Yamahas is pretty reliable, so look there last of all.

This could be one of several problems...
• Last year's fuel. Get some fresh gas.
• Every 2-stroke needs a new spark plug each year... you know what that means.
• Clogged carb jets due to storing the tiller over the winter with fuel in the system. Never, ever do that. Now you'll need to pull the carb apart and clean it. Most of the orifices are so tiny you can't see them. Good luck.
• Engine is so old the crankshaft seals have hardened with age. This is one reason no 2-stroke lasts longer than about 8 years. If the seals are shot, then it will cost more to fix than a new one costs. Time to toss it.