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2000 Arctic Cat 300 running issues..Please help!!


fireman2828

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My 2000 Arctic Cat 300 is having starting and running issues. You have to crank it over while putting your hand on back of carb to get it to try to start, then it will only start by flipping up decompression switch and pull starting. When it warms up, then it will start fine with electric start. Once it warms up, it idles fine for awhile, then starts to idle up to a high rpm, if you push down on shift lever and let up slow, it will then idle down. I just leave it in gear. It was having trouble running at full throttle. I took the carb apart and cleaned it and found the tube that the float needle valve goes into had a bad gasket and was letting to much gas into bowl. Replaced that and now runs great at full throttle. Don't know if I messed up any adjustments or not. Any info would be greatly apprecciated. Thanks, Brian...

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If it was hard starting before you dug into the carb the first thing I would check is the valve clearance.

I don't think the 300 has the auto choke so it can't be that.

Not sure what year the 300 was supplied untill but AC sold zuki engines (400,500,700) up untill about a year ago.

As I find more info I will post it up.

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It was hard starting before, but it didn't have the Idle problem. Before it seemed like it was flooding itself out, now it seems like its not getting enough gas, not sure. Once its running, it runs good. In the manual, theirs a screw in the carb that say to seat it, then back it out proper amount of turns, but doesn't say how many. I did turn it before I new what it was. Wondering it that could be the problem. Is their any other signs of valve problems? By the way, it has manual choke. it was froze open. I pulled it out and lubed it, now it moves free, but doesn't seem to help start it. Just kills it if it is running and you engage it. Thanks for help, this is getting frustrating...:aargh:

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Tight valve lash = hard starting or backfiring

Loose valve lash = noisy

Afriend of mine checks for noise from time to time with a screwdriver handle up against his ear on the tip on a valve cover listening for a good quiet tick.

The screw you are talking about is the pms screw. If it runs fine from 1/4 to full throttle it is either your pilot jet or the pms screw. Check the screw first and then double check you put the jets back in the right spot and there is nothing in them. One spec of dirt can throw everything off. On the newer cats it is 2 to 2.5 turns out. Not 100% with the older ones.

If you have the manual there should be a spec section like how much oil diff fluid etc etc. Try checking there.

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My book said to adjust pms screw out 2 3/4 turns. I did that and it did'nt change anything. Is valve clearance easy to check? I'm gonna read the book and see what it says. My book is not clear an things. Where is a starter jet? I did'nt take any jets out. couldn't figure out how. When it runs, it blows whitish clear smoke. Put hand over exhaust, leaves no residue, although once it blew water out exhaust. Thanks again for your help. It is appreciated...

Edited by fireman2828
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  • 4 weeks later...

Sorry havn't been back for awhile. It is oil cooled, not water cooled. After it warms up, the smoke goes away. I tried to romove the plug on bottom of muffler, but it won't budge. I took the carb apart again and removed the jet and cleaned it and removed the pms screw and cleaned in their. Did notice that the SPRING is missing from the pms screw hole. Will that cause a problem? Their is also a washer missing from the screw that holds the jet in. I changed the plug. It had carbon buildup on it after being cleaned recently. Still have to pull start until it warms up, then wants to idle high. I do appreciate all the advice you all give. thanks...

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First thing I would do is replace any of the parts that you have noticed are missing. Without the spring on an adjustment screw, the screw will not stay where you put it. A high idle could be caused by incorrect idle adjustment, which would not cause the other problems. The idle should be set when the engine has reached normal operating temp. It could aslo be caused by incorrect ignition timing, or an air leak, both of which could cause the hard starting issue. Air leaks are dangerous, so I would start by checking for leaks by spraying WD-40 around the carb and intake boot and listen for changes in the sound of the engine. If you find no leaks, check the timing and do a compression test. If the timing is off adjust it. If your compression test shows low then you may as well start tearing the motor apart, that could be caused by worn cylinder bore/piston/rings or valve sealing issues. In most motorcycle and ATV engines, 100psi or less is really an indication that the motor has little life left. Quick carbon buildup indicates oil in the combustion chamber or an overly rich air/fuel mix. If the smoke goes away after a short while, that points more toward leaky valve guides or carb float leaking oil or gas into the cylinder while the machine sits, but still could be a piston/cylinder problem as well.

Edited by DirtDemon
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The Idle problem started after I took the carb apart. I sprayed carb cleaner around, when I got to bottom of carb, it started to run funny. Is it possible to leak air through bottom (float cover) and not leak gas out when setting over night? If so, I'll replace that rubber gasket. If you leave it in gear, it idle's just fine, if it were timing, i'de think it would make it die all the time. It's a great machine after you get it started. Thanks again for the advise...

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I would not suspect that air leaking in through the float bowl gasket would be the problem since the float bowl is vented to equalize pressure and allow fuel to freely enter the bowl. However, if the fuel level is too low, then maybe, but the real problem there would be that the float is out of adjustment. I would be more suspect of the lower part of the side cover leaking, that is if you noticed this while spraying on the left hand side of the carb. Either way, I think it would be a good idea to replace all of the gaskets/o-rings in the carb since you need to get the missing spring and washer anyway. While you have the carb apart, check the diaprhragm at the top of the carb, make sure every thing is clean, pay special attention to ALL passages. It is good to blow them out with compressed air as long as it is COMPLETELY disassembled, you don't want to blow out any parts that may still be hanging around. There is also a small filter at the top of the float valve, you may as well get a new one of those too, it is only a couple of dollars. BTW, did you ever check the valve lash?

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No I didn't check valve lash. I have no idea how to. Is it hard to check? It was the left hand side that made the motor idle down. Which side cover? the one with the throttle cable in it? I didn't think that had to be air tite. I did take the top all apart and cleaned all of that and blew what I could out while I had the jet out. Is the finger screw out the bottom the only idle adjustment?

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You just take the valve cover off and slide a feeler guage between the cam lobe and rocker arm. They are adjusted by loosening the jam nut on the valve end of the rocker arm and screwing the adjustment screw in the center of the jam nut. Consult a repair manual or dealer tech for clearance specs. As far as the side cover leak goes, I think that the throttle cable cover is the only cover there is and I doubt that that cavity has an air tight seal from the carb venturi, so it should be air tight. Like I mentioned before, you may as well just replace all fo the o-ring gaskets in the carb, they are cheap, and you really should replace the missing parts you mentioned before as well. You will want to take the float bowl off too, if you haven't already, and make sure the there is no varnished fuel residue in the bowl, and make sure that the bowl vent is not clogged. You will also want to check the float adjustment. The fuel screw, or pms screw adjustment can affect the idle as well. It is best to get the carb properly tuned before you set the idle screw adjustment.

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Where is the bowl vent? does it come out through the rubber tubes out of carb? I've taken everything I can apart and cleaned, including the screen under float needle valve, and replaced that rubber oring, which was causing my original problem of flooding out. the float measurement is right on, pms screw backed out 2 3/4 turn, cleaned the jet that comes out center of carb. I will be ordering the gaskets and missing parts for the carb. When I get a chance, i'll check the valves.

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  • 2 months later...

Hey, been there, done that. You need to adjust the valves. We have a 2000 red 300 Arctic Cat and I have to adjust the valves every year. I have a 2003 green 250 and have never touched the valves. Go figure. But the 300 has 6000 miles on it now.

If you don't have a good service manual spend the $70 and get one, it can be a lifesaver.

Get the valves adjusted before doing any adjustments on the carb. Good luck

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  • 7 months later...

Hate to wake up a thread this old, but I have a 2000 Arctic Cat 300 that seems to spit and sputter when climbing hills. Yesterday I decided to try something different...I was climbing a hill on which this happened before, when I got stuck(Because of it acting up), I turned the fuel valve to the off position, after about 30 seconds, it seemed to balance out and carry me the rest of the way up the hill. I really think it is loading up with fuel. Now, I am trying to figure out why. I would like to adjust the float height, but I have no clue what it is supposed to be set at. Any clue?

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It may not be adjusted improperly, it could just be getting stuck. I would get a repair manual for your machine, anything you need to know about adjustments, torque specs and testing/troubleshooting procedures will be in there. Anyone who works on their own machines should have one. First thing I would do is just take the carb apart and see if there is anything that could be causing the float to hang up, dirt, gum, or some other type of debris.

Edited by DirtDemon
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Well, after messing with the float and the air/fuel screw(set at 2 3/4 turns out now) for a while, it is running a LITTLE better. Though, under heavy(ish) load, it still wants to cut out. I have had the carb apart quite a few times to check for sticking mechanisms and such, everything seems to be moving as they should. I have run compressed air through every channel, every jet, and even removed the emulsion tube and cleaned it. The only thing I have not done is replace the air filter. Though, nothing changes with or withOUT the air filter installed. I have tried different grades of gas, gas treatments, to no avail. It sickens me how well it idles, but when I REALLY need the power, it falls on its face. Maybe I have the float COMPLETELY wrong though. I have just been adjusting to see where it gets better at. I have no way of knowing what the float height is SUPPOSED to be. Being on disability, money is a bit tight, so a bit longer before I can buy a manual for the beast. Any help in the meantime is VERY MUCH appreciated. Thanks everyone!

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Well, tried out the quad after gapping the spark plug properly, though I did see SOMEWHAT of a difference, the underlying problem still exists. Slight hills, steep hills, even level roads, it just seems to pick an inopportune time to cut out on me. Guess I will have to wait until I buy a book to figure out how to check and adjust the valve lash. Oh, I did check for air leaks with MAP gas, surprisingly, I could not find a single leak. I do not have the compression tester to check for that either. I can not complain THAT much, it DOES run, I just can not climb hills or try to give it full throttle without expecting problems. But just to put around, it is a great ride, LoL!

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  • 6 months later...
Check those valves and let us know what you find, good luck.

Okay, so I am REALLY slow with getting things done. I FINALLY got around to buying a set of feeler gauges and checked the valve lash, turns out the intake side was WAY off. This solved absolutely EVERY problem I have had with it. I also checked the exhaust side, and it seemed to smooth things out a little further, but the initial problem IS fixed. Thanks everyone!!! I could not be happier with my ride. :)

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