GX390 idles, Won't rev

[Cdrew11]

Like the title says I've got a GX390 that runs, but now I'm having trouble getting it to rev. It starts and idles fine but it only revs when put on the choke. Using the throttle causes it to die...take my hand off the throttle, it idles just fine. I took out the spark plug and it's black. I was told that the engine is running too rich.

Any advice?

 

[TurtleMann14]

if the plug is black then yea its rich

check air filter and clean carb

inspect fuel tank

 

[Cdrew11]

The air filter is fine, This is the first time I've had the running. Prior, it was in storage drained of fluids.

Just as a side note, It revs when the choke is off.

 

[bajagokart]

sounds like the carb is running rich to me! i would give it a good cleaning and also do everything that turtleman said

 

[Kaptain Krunch]

Just as a side note, It revs when the choke is off.

It revs when choke is off? seems normal too me...

 

[Cdrew11]

No I mean..

When I turn the choke lever from the closed to open, the engine idles higher and higher, which is similar to revving the engine.

 

[TurtleMann14]

so its really running lean, but when you have the choke closed it runs rich....
(it rev because it burning off the excess gas). my guess is if you leave the choke open its will dies in a short while?

clean the carb and make sure there is no dirt/rust in the tank

 

[Cdrew11]

Haven't tried that, The engine idles way too high with the choke fully open for my comfort. When the choke is fully open it runs fast enough to engage my TC driver all the way

 

[anderkart]

Like the title says I've got a GX390 that runs, but now I'm having trouble getting it to rev. It starts and idles fine but it only revs when put on the choke. Using the throttle causes it to die...take my hand off the throttle, it idles just fine.

Make sure the carb/intake gasket isn't leaking for some reason. If your carb mounting bolts seem to be tight enough, try spraying some carb cleaner all around the carb/intake mating surface while the engine is running. If you detect any sudden change in RPM while spraying, you've just confirmed an intake leak.

I took out the spark plug and it's black. I was told that the engine is running too rich.

Any advice?

If you'd just been running the engine with the choke closed here, your black/rich plug reading would be expected. After you get the problem fixed and the engine running corectly, then take another plug reading.

 

[slideways]

What happens if you unscrew the idle all the way (turn it down) and try to open the choke?

 

[Sam W]

the same exact thing happened to me with a little b&s 2.5

its the fuel to air ratio i can almost guarantee it.

play with the 2 small screws on your carb

 

[mrfreyguy]

its the fuel to air ratio i can almost guarantee it.

Agreed. Sometimes when my bike sits for a while it dosent like to rev. Playing with the mixture helps everytime.

 

[TurtleMann14]

i guess if there is an air leak it would make it follow those symptoms as well

make sure your carb is tightly bolted and the gaskets are good

 

[Cdrew11]

Problem solved guys, It turns out that the stock throttle system made the throttle fully open. I changed the spring and moved the cable and everything worked right as rain.

Once I got the thing running though I ended up totaling my comet 40 series belt so....****.

Thanks for all the help regardless.