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I have a Ryobi 770reb weed whacker. I completed a rebuild and I've replaced the carburetor, fuel lines, fuel filter, spark plug and air filter. The weed whacker will start and run fine with half choke but the moment I cut off the choke the motor cuts off. I've tried both the old carb and the new carb with the same results. I would typically believe the issue was a gummed up carb but the new one has the same issue.

I have no clue where to go from here. Any advice would be greatly appreciated and thanks in advance.

Your machine needs the additional richness of the choke. Therefore your machine is getting too much air, or not enough fuel by normal means. That could be 20 things.

Did you even bother to tune the carburetor? Most are just sent in a will start tuned condition.

StarTech said:

Did you even bother to tune the carburetor? Most are just sent in a will start tuned condition.

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I did a little tuning with no good results. I dont think its the carb because both the old and the new carb have the exact same symptoms and the old carb was running fine.

Born2Mow said:

Your machine needs the additional richness of the choke. Therefore your machine is getting too much air, or not enough fuel by normal means. That could be 20 things.

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Oh boy...That sounds like a long hunt for the cause of the symptoms...Thanks for your input!

Chris Walker said:

Oh boy...That sounds like a long hunt for the cause of the symptoms...Thanks for your input!

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1. Start with new fuel and a new air filter. That would explain the lack of difference between old and new carb.

2. Then the carb adjustments. There is a Hi and Lo adjustment screw. Hi is for full throttle (aka "WFO"). Three guesses what Lo is for.

Get a trigger spray bottle with WD 40 or similar , not a spray can cause the propellent is very flameable .
Start the trimmer holding the shaft in a vice so you can use both hands to diagnose the engine.
Set the spray bottle to stream and slowly saturate the manifold region with the WD 40
If that makes no difference the saturate the pull start and the rear of the engine.
Ryobi 2 strokes use a 1/2 crank and the pull start , when fitted to the back is also the crankcase seal
If the pull start is at the tube end then there is a plate to seal the crank case at the back.
The gasket which makes the seal is very thin & easily compromised .

Gasket is 15
Reed valve is 13
The other oil seal is in the end of the crankcase 16 and AFAIK not replaceable