Acceleration stumble, 4 stroke

I have a Honda 300 EX, (I know, a quad, but it's fun in the snow....). The thing was in storage for a while. It starts fine, but when I bang the throttle, it cuts out so bad that sometimes it stalls. I can bring the revs up if I give it just a little bit of steady throttle, but like I said, if I nail it it wants to die.

If this were a 2-stroke, I'd think dirty jets. Since it's a four stroke, it could be that or maybe the accelerator pump? The thing is a bear to get to, so I'm looking for some direction to go before I just start tearing everything apart.

If you think it sounds like the Acc. pump, what should I look for to fix the problem?

Thanks in advance.

H

So just a good ol' fashioned carb cleaning, eh?

I'll give that a shot sometime after the mercury gets above freezing and I'll let you know if that worked.

Thanks for the replies.

H

An Update and appeal for further advice

I did a good carb cleaning today, the pilot was dirty and I was hoping that was the problem. It helped, but didn't get rid of the stumble completely.

As far as I know, no carburetor settings have been touched since before this problem developed, so I was hoping this would cure it.

The motor still has a stumble that comes when you punch the throttle. Enough to kill it sometimes. It revs up just fine if you're a little more smooth with the throttle, but punching it kills it. I can't tell if that's too little or too much fuel.

Anybody know what the stock air screw setting should be for this beast? It was 2 1/2 turns out.

Also, it has an FMF pipe and silencer, but this was installed long before the problem surfaced.

Okay, fire away.

H