I just bought a 1996 King Quad 300. It ran like a scalded cat. I noticed there was no oil in the site glass so I changed the oil. I inadvertantly over-filled it and ran it that way for a mile or two and then it started to act sluggish. I drained the oil down to the proper level, cleaned out the air-box and replaced the foam filter. I even rebuilt the carb and there was some gunk in it. The original main jet was marked 117.5 and the jet in the rebuild kit was 120. I looked it up in my manual and it calls for 120. Anyways, I started it back up and it still runs sluggish. Could I have a problem that coinsidentally started after the oil change. Maybe it's not getting enough fuel. How do I check the operation of a vacuum operated petcock? I opened it up and the diaphram looks OK. Could it be the fuel pump? How do I check that? Thanks in advance for you help!  

most likely you have some oil overload in the head around the valves, you could have also gotten alot of oil in the exhaust. you should have a drain plug for the muffler.

it could be that the 120 jet is allowing too much fuel.
if so it will bog down.
you can take it to a shop and them vacuum test it, (costly) or you can take a flat screwdriver, and try adjusting the air/fuel mixture. to see if you can straighten it out yourself.
but i would check the exhaust first, and let it sit overnight to drain any oil back from the head.

if the muffler is full of oil it will act sluggish, and if there is a load of oil on the valves it will try to burn the oil with the gas making it sluggish.  

Thanks for the tip. I went out to the garage and tried draining the exhaust and it was bone dry. I'm starting to think the high oil level wasn't an issue because when I changed the foam air cleaner not much if any oil appeared to have gotten into the air-box. Is there a way to test the petcock and fuel pump? Thanks again!  

if you are getting fuel to carburetor then the fuel pump is working.

if it's running it's getting fuel and the fuel pump is working.

if you overfill the engine oil it has no choice but to get sucked up into the cylinder head through the intake valve(s).
You could have an excess buildup of carbon on the valves which could cause a loss in power.
you wont find any in the airbox or filter most times. it doesn't normally flow back to the air filter because the air filter is an inlet. but it can get into the carburetor
being the carburetor is bolted to the cylinder.

also check the exhaust pipe before the muffler. it could have some oil puddled in there restricting air flow.

recheck the carburetor too, you could have gotten more oil in there after cleaning or rebuilding.

hope this helps  

You'll have to excuse me as I'm not that mechanically inclined, but I opened the lower valve adjuster cap and oil poured out...is that normal or is that some of the oil your talking about? Your very kind to help me (and others) as I can't really afford to take it in to a shop.  

with it not being run for a while you shouldn't get much oil out of it at all
of course understanding that the valve adjuster caps are normally higher than the crankcase.
all of the engine oil should drain back down into the crankcase after awhile with just a very small amount of oil coating the valves and moving parts.
while it is running, oil should be flowing, and you'll have more present.

did your oil level go down in the glass when the oil spilled out from there?
i'd bet it didn't, but check the oil, just in case there is some strange design to valves that iam not aware of.

if you didn't lose any oil in the crankcase oil level glass, then the oil was buildup oil from over filling it.  and to be safe run the engine for a few minutes and recheck the oil level. it may run alot better now.
but keep an eye on it for a while as you ride it the next few times.

and i don't mind helping troubleshoot, i have been working on atv's and dirtbikes for years, and actually enjoy it alot.
and it doesn't hurt to help a fellow rider.
besides like i said, i enjoy it alot.
sometimes i'll take a little time to think about one before i answer, but i try to answer as many as I can.
I know repairs can be expensive, (i own a cycle repair shop specializing in atv's and dirtbikes.) and i know sometimes we don't always have the money to just run out and have it fixed.  

Well, I know there are alot of things you could do with your time, and using some of it to help others is WAY cool! Level in sight glass stayed between the two marks. About a full cup of oil came out when I opened valve cap. Do you think that's enough to make a difference. I'm in the process of pulling the exhaust away from the head, quite a chore as there is no drain port on the pipe that I can see and everything is tucked in pretty tight. I'll run it tomorrow and post the results.  

I think it could make one heck of a difference!!!
although it is possible that you have some lasting problems from overfilling. but chances are equally as good that it could come out just fine.

see the problem is, if the valve is covered in oil then it doesn't breathe as it should.

you should have 2 valves per cylinder, one for intake, to draw in fuel to burn, and one for exhaust,
they should have oil on them, but not a cup of it.
and you shouldn't have very much oil on it when it isn't running.
but if the exhaust valve has that much oil on it, then the exhaust pipe probably has some in it too.

it's kind of like stuffing a potato in your cars' exhaust pipe. it wont run very long before it runs feebly, then it will quit running altogether. ( no don 't prank your neighbor and put a potato in his tail pipe, no matter how much he whizzed you off.)
when you have a ton of oil on top of the exhaust valve
it cannot exhaust well enough and you end up with excessive backpressure on the cylinder causing it to not draw in as much fuel.
it will run weakly if it runs at all like this.

It does help that when i post a reply to someones' question here that they do really appreciate it.
meaning atvrideronline has some awesome readers!!!  

be sure to let me know how it turns out.  

Good Afternoon, Wolf. Ok. Day Three. Still no top-end power after oil drained from valve cap. According to the book, removing the exhaust is a painful 25 step process that suggests removing rear wheel and shock. I'm seriously considering drilling and tapping my own drain hole in the lower most portion of the exhaust pipe which is four or five inches from the cylinder head. Is this a good idea or am I thinking out my arse?  

if you thread and put a good threaded plug in it you should be fine

it is possible that you have also cooked a valve, or blew out a valve stem seal as well.
buti'd make sure the exhaust pipe is clear before going any further.  

I don't know where you are in the u.s. but if you are close to or in the chattanooga tennessee area bring it by and i'd be glad to help you figure it out.

I forgot that you had said that the jet was changed.
it could be getting too much fuel as well this also causes weak top end.  if it is bogging down on top end or at the top of the gears, then chances are it is getting too much fuel.

does it run fine until you get to the top of the gears range or bog down when you get on it?

if so then you are most likely looking at a fuel problem.
but it does sound like you have worked out some of the oil overfill issues.  

That would be awesome but I live out west in nevada. The quad used to really pop off the line but now, since the oil incident, it's just weak throughout the throttle. I still need to drain the exhaust (if there is anything to drain). I just got done watching the Super Bowl so I may go out and try it tonight. If not, then first thing in the AM. I'll keep you posted. Thanks Wolf.  

Also, I'm not sure if the main jet is an issue. It might be, but actually the book calls for a 122 and I put a 120 in it (that was what was in the Moose rebuild kit). It had a 117.5 maybe because it was rejetted for altitude? I'm at almost 6000 feet. Are'nt you supposed to lower the amount of fuel for high altitude due to lack of oxygen? I still need to tap the exhaust then I'll go from there. Thanks Wolf.  

Also, I'm not sure if the main jet is an issue. It might be, but actually the book calls for a 122 and I put a 120 in it (that was what was in the Moose rebuild kit). It had a 117.5 maybe because it was rejetted for altitude? I'm at almost 6000 feet. Are'nt you supposed to lower the amount of fuel for high altitude due to lack of oxygen? I still need to tap the exhaust then I'll go from there. Thanks Wolf.