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Discussion Starter #1
I need a hand getting my 600 tuned in. It has a big hesitation when accelerating then backfires on deceleration. When I choke it there’s a good bit of black smoke then clears right up when I take the choke off. I’m thinking none of this is supposed to happen. My dad is thinking it’s lean because of the backfire but the black smoke is telling me it’s rich. Any thoughts are appreciated


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It's running lean.
If you run it with the choke on constantly, it's going to make black smoke because the choke is actually an enrichening valve, meaning it's dumping un-metered fuel in the engine.

Have you ever adjusted or had the carb off and apart before?
Have you ever touched the pilot needle adjustment?

How clean is the air filter? The 600 is very temperamental on having a clean air filter.
 

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Discussion Starter #3
I don’t need to run the choke all the time. I have cleaned the carb and tried adjusting the needle one place up then down and haven’t seen much of a difference


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The main jet needle is not the same as the pilot.
The pilot is located on the bottom of the carb, on the engine side (not airbox side), and requires a small flat screwdriver to adjust. This must be a certain amount of turns out from seated position. That is your starting point. Then you can make small adjustments to tune it for your specific application. The adjustments are no more than 1/8 turn at a time, if required. If you have a completely stock setup, then you should never need to adjust this.
So the question is, did you ever change the position of this when you took the carb off to clean it?

Additionally, moving the main jet needle clip down (raises needle) enrichens the fuel mixture but only when running above idle rpm.
 

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Also make sure none of your carb boots are cracked or split especially the one from carb to intake
 
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