I have a slayer pro, its 1 tank into break in. When its running, it has a tendency to move unless brakes are fully applied and when brakes are off it will accelerate to a decent speed. I tried adjusting idle speed but since its in break in i don't wanna, mess with carb settings much. Any ideas? Its been a long time since i was in the hobby. Thank you

You are sure the trimm is correctly adjusted to close the carburator at idle?
Maybe an extra return spring is needed?

Like already mentioned above, make sure throttle trim is at neutral position.

If this is not the problem, check your idle gap, make sure it is not set too wide. Re-adjust to 1.0-1.2 mm (good for first start up).
Now richen (CCW) the low speed needle (LSN) a few hours at the time, until the idle speed drops to a point that is stable enough,
but the clutch does not engage (truck does not move forward).

Enjoy breaking in your engine

I plan on double checking the throttle is neutral when sitting later today. As far as the idle speed screw goes it didnt seem to make a difference in idle speed it would stay at the same rpm then either stall from being too lean or rich. I put it back to about where it was i will adjust it to the spec you mentioned later.

i adjusted the idle speed to the spec given, adjusted the throttle trim and it still takes off at idle. Anyway it could be slipper/bell clutch?

i adjusted the idle and trim nothing helped. What else could it be?

Did you take a close look? Take off the ait filter and put the radio on.
When slowly giving throttle there need to be a small movement of the servo before the carburator will be opened. If that is not happening then there is something wrong with the trim or total adjustment of the throttle link. Also be sure when letting the throttle go the carburator must close, check it by pushing on the throttle link at neutral position to see if the carburator does not move.

If that is happening then there must be something wrong with the idle screw or maybe the LSN screw.

The only thing I miss in your post is when you put the car on the brake, is the engine going down on rpm or does it stay on the same level.

ill check to see the carb movement tomorrow, i have the trim set so the linkage moves before the carb and when its stopped via the brake it will remain near where i think it should idle but once brake is released it seems to want to pick up speed to a given point, running lean i assume since the pitch is completely different and no smoke is being given off. Also when its cold the car drives like it should, its normally only when warmed up i have this issue

Then the engine is set too lean. Richen up booth needles or try to go back to factory settings (if listed in the manual)

Here are a couple of things to check. First make sure your throttle linkage is not binding and the carb is closing all the way. Also put a throttle return spring or band on it to ensure it also closes in the event of servo failure. Second item, Check the clutch and make sure it is built correctly. Ensure the bearings are good, the clutch bell should have about a 1mm of play back and forth and should spin freely when you spin it by hand if the engine is removed from the car. If it does not, it is not shimmed correctly or you have the shoes assembled with a problem. If the shoes are engaging the same thing will happen that you are referencing.

Its probably already been said, but reducing the idle speed screw during break in is normal as to that your location and climate may be different then what it was set for from the factory. I would recommend backing it out 1/8 turns at a time until you get a smooth and steady idle. Reducing the idle is not going to damage the engine in any way. Also only make screw adjustments after the engine is warm and you have made some high speed passes to clear the engine of excess fuel.

Remember that he is trying to burn his first tank of nitro, during the initial breaking-in of the engine. No high speed passes yet.

So to me it would make more sense to keep richening (CCW) the LSN needle a few hours at the time, until the idle drops to where he want it, due to the mixture becoming richer like that.
All this while leaving the idle speed screw as it is set (1-2 mm). Like that, it is guaranteed to have a super rich initial setup.
This setup is good to lube the engine and basically pump a lot of oil through the engine to flush out any metal dust in it and remove the micro-bit of metal particles that are always released initially during break-in. After that (the initial 2-3 tanks), he can start leaning the engine / backing up the idle screw to a leaner / faster setup.

Just make sure that the carburator barrel is not hanging half opened, when you let the throttle go lol. That's all.

EDIT: And if you think that the engine idle speed RPM is correct and not too high, then see what the genleman wrote above ^^^

If the idle is correct and the truck is still running away, something is wrong with your clutch shoes / bell setup.

Pull the engine out and have a look at your clutchbell and clutch shoes and springs.

Good luck,