I havnt seen any other problems with the stock springs in any threads so Ill assume you have a problem in your twist/lever throttle being too tight, your cable having a too sharp a bend in it or some thing sticking in the carb/linkage. Make sure you lube every thing with wd40 and every thing is free to move to let the spring do its job.......make sure the cable housing ends arent crimped too tight to restrict the movement of the cable through them also. Could just be way out of adjustment too.
Thanks for the reply. I did some more investigating and I believe the problem is in the carb. I am new to this so please excuse my ignorance. There are no and the cable is moving freely but when I turn the throttle it does not spring back to idle position. So I took off the carb to see what was going on. This is where I am lost. There is a spring inside a brass sleeve and the cable is inside the spring and it goes through the slot in the brass sleeve. There is a needle that goes into a hole. It seems as if the brass sleeve is too tight and does not move very easy. Should it be like this? Also, when it is at full throttle the pin should be out of the hole correct. I am not sure how that mechanism works. Thanks.
The carburetor slide should be ablt to slide up and down very easily. Check the slide hole on the carburetor to see if it is out of round.
Some folks have needed to sand the slide a teeny bit smaller in diameter with fine sandpaper.
Also overtightening the slide cap on the carburetor is a no no. It will distort the slide hole.
Most of the time I found they dont always go back to close throttle position but once the engine is started, the vibration fixes that, the twist throttle wears in and springs back normally after a few runs..