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Discussion Starter #1
Hello everyone,
I'm having a problem thats been going on for a while now. My Arctic Cat 300 runs great , but smokes when it reaches a certain rpm. The smoke smells like it would be a gas problem. I purchased a carburetor kit and it solved the problem for about a week or two and the problem is coming back. The ATV has low hours on it, and I have already replaced the valves also checked the bore for excessive wear. Everything looked good. For any of your guys help I thank you.
 

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It has been a while since I owned an ATV with a carburetor, but tuning a carb is kinda fun. 2 Things come to mind for yours, either the main jet is too rich or possibly any crankcase vents going to air box are plugged causing excessive base pressure. Check that oil is not overfilled too. One thing that always helped me tuning carburetors was to buy a Dynojet kit. The adjustable jet needle is very helpful and having a few main jets to try makes final tuning easy. What I do, start with getting it to idle first, then tune the jet needle for best midrange and lastly, play with different main jets. Start lean, run it wide open, write down top speed and do a "plug chop" to check color of plug. Next try 1 size larger main jet, same procedure , eventually, speed will go down, plug will start to look rich. I try to go for the one that gives top speed. Check that all of the rubber boots between carb and motor.
 

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Are you shutting the fuel off when you stop ?
 

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Discussion Starter #4
I wasn't really wanting to get technical with my carbeurator I just want my atv to run and ride smoothly. It only has a fuel flow mixture screw at the bottom next to the float bowl. I checked with my manual and set the screw to the right specs.The plug has a nice and blue spark. I do shut off my gas at the petcock when I get done riding for the day.
 

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does your OIL smell like fuel?
as maybe carb float is sticking and flooding your oil with fuel!
even new carbs and or rebuilt one's can have this happen!
 

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Did you replace the needle and seat?
 

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well, this is going to be a guess on my part
BUT since this is not a brand new atv here
I would 1 , drain your fuel tank
as it sounds to me like you have dirt in your tank, as if you completely rebuilt and cleaned your carb, and flat is NOT sticking afterwards
that says to me NEW dirt got into your once cleaned carb!

this is rather common on older atv's
folks clean carb, then have issue's still and the reason is, you NEED to go up spotream of the issue to prevent it from returning

SO< to rule fuel system out, you, 1 drain fuel tank
2 clean fuel tank
,3 clean fuel peacock
4 IMO< Throw old fuel lines out and replace with new one's there cheap
Ethanol fuel causes lines to get a coating on them that builds up and can flake off, just like it coats parts ina carb, peacock and so on
5 CLEAN carb again, and I don't mean just spraying down with carb cleaner
I mean clean out all passages and make sure there is not varnish like coating on parts, some times, you realaly have to work hard to get things clean, or use a ultra sonic parts cleaner, boil hard parts in lemon juice or the likes, NOT just spray with carb cleaner as that does NOT do much at all to carb/ and its parts!)
and check and set float to proper spec's!

6 start with ALL new fuel

SO< if you do the 6 steps, you know for a FACT all is well
and then any issue's should all be gone
skip any step and you can have issue's till the cows come home LOL

NOW also, if you GOT fuel in your motor oil, you NEED to change it ASAP
as if not fuel in the oil can cause seals to go dry and make for larger problems down the road for you!
its NEVER good to have fuel in your oil,also thins the oil and the protection it supposed to provide to motor parts!

make sure you ALSO change oil filter too!
and I would be doing a SECOND oil change rather sooner than a normal period of miles/time! to make sure its ALL out!

when a float sticks or hangs up, it causes fuel to fill into the crankcase! and is a rather common issue with this crappy ethanol fuel we all have anymore!
 

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Then install an inline filter.
 

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Discussion Starter #11
I have drainded and cleaned the the fuel tank about a year ago and petcock about four months ago when I started fixing it to get it running. I washed it several times and made sure I got every bit of it out. I also replaced the gas hose with a fresh new one. I have cleaned the carbeurator several times with a small wire and mini brushes. Like I said I purchased a rebuild kit and replaced the needle valve sleeve and needle valve along with the jets and gaskets as well. This ATV might be old, but it has very little hours. It ran great when I purchased the rebuild kit a bit back. I thank you all on your helpful info.
 

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Discussion Starter #12
I almost forgot I do need to change my oil soon it does have a scent of gas in it. I also can't install a inline filter due to it being gravity flow, and lacks receiving fuel to the carbeurator.
 

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I had a carb that I cleaned and cleaned, replaced every part. Put it in my friends ultrasonic cleaner for 15hrs, bike still ran like crap.

Bought a new carb problem solved.

Sent from my SM-G965W using Tapatalk
 

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well hate to bust your bubble
but 4 months is a LOT of time for both fuel to go bad and or dirt and crap to get into your tank!
NOT saying it did, but saying it is more than possible here, ethanol fuel is know to go bad FAST, and some times in a few weeks IF this
all comes down to how long its been in the holding tank'
which also is where dirt can get in..water too
so, just cause you cleaned the tank, 4 months ago, doesn't mean fuel and tank are clean NOW

next using a rebuilt kit again, great idea, but doesn't make for a perfectly clean carb, as again this crappy ethanol fuel, coats things with a varnish like coating, and its extremely hard to remove once its on there, and it can cause passages to be of improper spec size and cause flow issue's
plus don't forget that carb 's can wear out too, ?

the fact you have fuel in your oil ,says a float is sticking and or not set up correctly IMO
so, one way or another, that is a issue still for you, or was?
and you ran the motor a longer enough time with fuel; in the oil to do damage to some seals and now your getting oil by passing things and causing your smoking issue!

I would try doing a compression test here and what does the spark plug look like ??

Last question I have for you and just asking, is this a OEM carb, or an aftermarket carb?
as sadly many swap to after market carbs due to there cheap and most SUCK, some work great many DON"T
I would again pull and clean carb and make sure float is working properly!
DO a compression test,
and then change oil/oil filter and see what happens!
drain oil replace oil filter,
 

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Discussion Starter #15
I haven't run the ATV long enough to damage anything internal. The oil has a mild scent of gas not critical, but I get your point it needs changed soon. The compression is 182psi, and the spark is nice and blue. I have the stock carbeurator, negotiated on buying an aftermarket carb but now scared to purchase one now.
 

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I haven't run the ATV long enough to damage anything internal. The oil has a mild scent of gas not critical, but I get your point it needs changed soon. The compression is 182psi, and the spark is nice and blue. I have the stock carbeurator, negotiated on buying an aftermarket carb but now scared to purchase one now.
I am no expert but a 182 PSI for compression is CRAZY HIGH, I would get a service manual and see what it i supposed to be at, and make sure you are checking it properly!
most atv's motors are at about 80-125 psi?
so 182, is off the charts IMO! LOL

and I was asking HOW does the spark plug itself actually look, not color of spark!
and damage internally doesn't take long to happen at a few thousand RPM's going on while running' if seal get damaged from fuel running a motor with fuel or not going/not going where it needs to can again do damage faster than one can think
and I am NOT saying you have motor damage, just saying
it only takes a small amount of run time to have damage happen inside a motor!
 

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Discussion Starter #18
I re-tested the compression. It tested 120 something psi with the carb closed, and 170 psi with the carb open. I also removed the plug and it's carbon and wet and has a scent of gas on it.
 

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that compression reading sounds more like it LOl
and again it sounds like you have a fuel/carb issue
as well as that fuel in the oil!

the wet plug is saying your having it!
to wet drowning out your spark to fire!
 
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