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Old 06-24-2009, 08:35 PM
Walter Keller Walter Keller is offline
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Default tuning gx390 carb on a 6.5hp clone?

Got a champion 6.5hp clone with an AGK intake manifold with a gx390 carb and a uni filter. As far as inside the engine we have 18lb valve springs and have removed the governor.

The problem is that it dosn't want to idle with the stock gx390 carb jet.

Any suggestions on the correct jet size?

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Old 06-24-2009, 10:21 PM
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Chances are the 390 carb is a bit fat on the idle side. Open up the air bleed some.
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Old 06-25-2009, 11:36 AM
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Didn't you already post that picutre up in another thread Walter? :p

(Or is my memory just a-funkin away?)

YES! Finally, I know I'm not alone in the GX390 carbuertor trouble world. My new one was leaking gas through the air filter... smoked like **** on idle, and... high uneven idle.

Gave it up and switched to the stock carbuertor. Next trying the 22mm Mikuni.
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Old 06-25-2009, 09:42 PM
Walter Keller Walter Keller is offline
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Default carb issue

Yea I did post these awhile back - the project kinda got back shevled then but its back on top now.
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Old 06-26-2009, 05:18 PM
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I think you need a smaller main jet in your gx390 carb. Its jetted for an engine thats nearly twice your clones cc's and probably running way to rich. (pull your spark plug and see if shows thick black soot)

I've made smaller main jets by soldering up the origanal jets hole and then re-drilling a smaller jet size with number-bits. (avalible at good hardware stores)

Your motor is close to stock so I'd start with a main size just a couple number-bit sizes larger than what your origanal clone's carb had. Sometimes it takes a few tries to find the best jetting and its always best to start small and work your way up to richer jetting as needed. (just make sure its not too lean)

Your karts overall performance, its ability to idle, and reading the spark plug will tell you when your jetted corectly.

Here's some info on reading plugs and jetting: http://www.google.com/search?hl=en&r...&aq=f&oq=&aqi=
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Old 06-26-2009, 08:41 PM
Walter Keller Walter Keller is offline
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Thanks for the info - we will be rejetting the 390 carb for sure
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Old 06-28-2009, 08:42 PM
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You are most likely going to need a bigger cam to offset the need for that carb. Not much sense in trying to stuff more fuel/air into something that isnt asking for it to begin with (stock cam and stroke).
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Old 06-28-2009, 09:42 PM
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i would try the idle jet
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