Set the air screw to 1&1/2 turns. I have slack in the throttle. Sprayed carb cleaner on the brand new carb boot, BOOM idle went down. So it's an air leak between the carb and the engine.

 

That'll do it. Spray around the base gasket also. I'd still go after crank seals on something this old also. To be 16 years old and sitting with fuel in the crank case for 5 years without running.. That may also be part of it also. Cheap parts but does take a little work to get to them.

 

New development!!! ATV runs but idles high. I can turn the air and throttle screw every witch way and nothing seems to get the idle lower. ALSO the idle has run away from me twice, as in full throttle. The best part is I could not shut off the machine!! So here i am standing next to my ATV, it's running at full throttle, pulled off the gas line and the spark plug wire. STILL RUNNING!!! Put my hand over the intake, to starve it of air, nothing. The only thing that killed it was flooding it with the choke. Any ideas on my possessed ATV now? Should I just buy a new carb? Should I just light it on fire and push it down a hill?

 

Did you address the leaking intake manifold or the crank seals? If not it doesn't take much for one to run wild and diesel if it's too lean.Air box and filter have to be installed as well.Checked that the throttle cable isn't binding or sticking at the carb or oil pump? Made sure you good fuel flow to the carb and that the carb is assembled ok,jetting is correct,110 main,40 pilot? Still sounds like it's sucking in way too much air for the fuel being supplied.They can get hot real quick and the engine will race. I've had this happen on atvs and water craft and most of the time it was air leaks causing it.

 

Remember that even though you pull the fuel line in the carb or shut off fuel flow, there still is fuel in the bowl on the carb. As for the ignition, I could see in a very lean condition, it will make parts of the piston or spark plug glow red causing the motor to still ignite the fuel mixture. I would be curious to see the condition of the plug. Is it bright white? That would indicate a lean condition.

Mike

 

Hello,
Were you able to figure out where it is getting air around the intake boot? Is the item in the link below the part you replaced? Did you make sure that it has a good o-ring or paper gasket under it that did not get damaged?
You could try removing the intake boot and put a thin covering of RTV sealant on the metal around the outside of the o-ring. This wouldn't be a long term fix, but it would help narrow down.
Also, high idles always indicates too much air to too little fuel ratio, or a mechanical issue (stuck throttle.) Choke restricts airflow which increases fuel to air ration. Rich condition would be a boggy throttle response or slow, sputtering idle.

All the best!
Intake boot-
https://www.denniskirk.com/18512.sku?utm_source=google&utm_medium=cse&gclid=C jwKCAjw7frPBRBVEiwAuDf_LW71fefYI26kuuAEonskPuCTSof kaQuAAClXB70PtzhbaGzFPZpPshoClp4QAvD_BwE&ad=154639 535946

 

Intake manifold has a built in o-ring,but on some of the aftermarket ones like this one,I wouldn't trust it compared to the oem.I'd use some silicone all around the metal part.

 

Hello to "Lucky girl and Old Polaris tech" and all..Just new here and man you guy's are spot on...but my prob is different ..so be kind of patient if you will....2002 Polaris Trailblazer 250...new carb kit..had to replace carb/oil injector cable , yep that was fun but all this time It don't want to start without FULL CHOKE...now when it does start.damn thing will idle all day long and runs great!.restart right away and it fires right up..but turn off engine for 10 minutes...full choke and a pain to get going again...at witts end ....I have heard prolly the top end...Could the top end really be a starting issue? ..or am I missing something...runs great when it's running....It's a fun little quad for riding around here in the pines but wish more reliable.... Thanx for taking time to read first post "Highpines"

 

Decent compression is at least 120psi or so.Yes,low compression can cause hard starting when the piston and cylinder are cold. Once warmed up a little they can crank again easily because the rings may seal a bit better. BUT If compression starts getting too low, the piston condition can reverse. Rings can lose their seal against the cylinder when the engine gets hot,then they can lose power and die.Won't start back up until cooled down. Compression around 95 to 100psi will usually allow one to crank,but if it's that low you need to address the top end plus I'd replace the crank seals while you're at it.My two cents though on doing just a top end only is that it's just a partial repair. Check the rod out carefully for any up and down play.Side to side is ok. If there is any play, a rod kit and crank bearings are needed.A lot of people have found that out the hard way when rods spit bearing chunks up into the cylinder and took out that new piston they just installed.

 

Thanks so much..great information..will be doing top end in spring after snow is gone..For now get er started take a putt ...