i have a mammoth st and i can get it tuned at ne of my lhs and i need to learn how to do it. but i reset it to factory settings and it still revs up and stays revved for a few seconds after i let go of the trigger. i was just wondering if someone could help me out
thanks

idle or throttle trim maybe....lsn too rich also could cause that.....your manual will explain tuning better or on rcu search for rc car tuning tips....i'm sure there's loads around...tuning a nitro engine is just a patience thing...you either have patience to be able to tune properly or you don't.

good luck with the mammoth st...their sweet lookin and welcome to rcu also

definatly try a search, there is plenty of great info on here. but for now it does sound like your low end is too rich. this means that when you let off the throttle, the engine gets overloaded with fuel and cuts out. that means that you need to adjust the low speed needle to lean the mixture on the bottom end. but before you do that it may be a good idea to make sure your top end is properly tuned. its not unlike tuning the low end, you just adjust it so that the engine sounds crisp and clean on a full throttle run and you can still see a thin smoke trail. after you are sure the high speed is adjusted properly you can tune the low end so that it will idle reliably without bogging down or cutting out. tuning normally just comes from experience, so be patient.

Re-setting to factory settings isn't the cure for a bad tune. All it does is give you a safe place to start from.
I recommend getting a temp gun(if you don't already have one).
Don't try and tune a cold engine...The engine's requirements will change until it gets to operating temp.**widely accepted temp range...200-275 degrees F.**

More fuel is more oil, therefore it runs cooler.
If it has 'too much' power all the sudden, or if it revs up, and then cuts out with the throttle at WOT, then it's too lean in the hsn.
If it keeps reving for a couple of seconds after releasing the throttle, and then idles down...lsn possibly too lean.(I'm not 100% sure on that)
If it sounds 'bubbly' when it idles, and lots of excess fuel dripping out of the stinger, then lsn rich.(notice I didn't say 'too' rich?) I run my engine a bit rich in the low end, so that if I want to, I can leave it sit and idle for a full minute, while I run into the garage for screwdriver. That isn't tuned for optimum performance, though. If I leave it sit for an extended idle, then it has a tendency to load up, and be real doggy when I throttle it again. But it's easier for me to spend a couple of seconds clearing it out, than it is to take it back to the bump box, and restart.

You just need to keep in mind the basics, and then develop a personal relationship with your engine.
Good luck.