Acceleration stumble, 4 stroke

[Hman]

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

 

[RMcommando]

My XR did a similer thing. Check that the spark plug is not blacked and clean it. Clean the carb and air filter. If you need to, change the engine oil. I did this to my xr and it ran fine after, i'm not sure about the acc pump.
cheers

 

[yz125_894]

you said it was in storage so it is prob just gumed up jets. Just enough fuel is getting in when it idils. Check the carb spray everything down real good with carb cleaner

 

[jboomer]

You also may be a little lean on your fuel screw, try turning it out a quarter to half turn.

 

[Hman]

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

 

[Hman]

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

 

[fuzzy]

Sine you just checked the carb, that rules out a crappy accel pump, right?

I'd say your too lean. These symptons are exactly what a lean-bog is. Air screw setting are for the pilot portion of the throttle. You're pinning it to create the problem, which means your main jet is too lean--try one size richer....