please help my os r2102 won't drop down to idle quickly even when very rich (carb back at factory setings) the more you try to put a tune on it the worse it gets.things i've tryed sofare throttle closing properly,new plug,fresh fuel,rebuilt clutch,new engine bearings,new rod and checked for any visable leaks.don't want to run a new engine in incase some thing else is causing the problem.any help on how to find the fault.

Try new fuel tubing to the tank and to the pipe, try different pipe, try different gas tank cap might be leaking, also new o rings in all 3 needles, or try a whole new carb if u have. I am not knocking u but it most likely its just not being tuned right i dont know your tuning level of skills but sometimes happens to the best of us. Also check when you tighten the screw that holds the carb i, make sure its really tight then try to turn the carb back and forth, os has a problem the barrel of the carb that goes into the engine is not one piece!! like a nova there is a sleeve pressed over the barrel why i do not know instead of just one piece but if its loose and it does come loose u will know no matter how tight u make that screw the carb will still turn.
If it does happen u either get a new carb or i take the sleeve off and use jb weld and slide it back on.

thanks ralph,a lot of what you say where my next things to try.do you think it's posible the carb or the fuel tank/line has a leak when hot that is hard to find when its cooled down.do you think it's an air leak or could any thing else cause these problems.i'am not the best tuner but richening up always cures a hanging idle for me exept in this case

thanks rick...

Sometimes yes very hard to find like if its the tank cap or a pin hole in the tube. Again I don't want to insult you but I think its the tune, is there anyone else u race with that knows how to try a tune on it as well?
Also next time u start it while it is idling high with the remote hit the brake and let us know if the sound drops even a little bit thanks,..

Is it a high pitch idle or a normal idle but high?

thanks for the repleys,when you hit the brakes you can tell it's lean,if you tune it real rich and do a standing start you can go from rich bog then hit the brakes as soon as it starts to clear out it will hang lean for about 5 seconds then start to droop down. had some help from one of the top guys same results as me try to go any where close to a race tune and it gets worse
checked every thing over today carn't find anything. could bad fuel cause this?

Bad fuel is possible but would make it more up and down, maybe a video if u can and some things to do for us so u don't have to redo it, while its idling high hit the brake a few times with a few seconds in between pushing the brake do hit the throttle just pump the brake and bake to neutral, then same video take the screwdriver and turn the idle screw all the way out almost till it falls out. if nothing do one last step turn the low end screw all the way out till it almost falls out. then stop the video, also just zoom in on the high speed screw for a sec or 2 thanks...

thanks ralph carn't get to the track for a while and its raining....

Don't just check the fuel line, replace it, just in case. It may have a tear that you cant see. Also make sure there isn't any fuel around the exhaust exit on the motor, if there is, replace the gasket. Same thing with the header to pipe gasket. Also, look around the area where the carb goes into the engine case, is it wet? You could have a leak there, make sure the carb is pushed all the way down into the case. Look at the area around the glowplug, is that wet? You may have a leaking head button. From you description it sounds like your bottom end is super lean, I would back off the needle a lot and see what it does.

sounds to me like you need to completely take carb apart and clean it. a all of a sudden high idle speaks fuel restriction to me. what are your temps at idle? abnormally high temp would indicate a leaner setting.

The usual symptom for high idle rev then drop is due to idle gap is to big. If you are at full throttle and release, and the engine stays reved high then it slowly goes back down to idle, it is usually idle gap.

Set idle hap to .5-.7mm. Once engine is at running temp, try and get the HSN set first. Once that is done if the revs are high and slowly drops to idle, close the idle gap and lean the LSN.

You mentioned all the replacement parts you did to the engine. How many gallons of fuel and how is the compression. Especially when the engine is at running temperature?
But as mentioned before make sure the head button is seated correctly. Same for the glow plug. I spent most of a day chasing a similar issue as the one you are describing. Come to find out the head button was not sealing properly. Put a new head button and all problems were solved.

I've had issues with air bubbles in the fuel line to the carburetor causing engine to lean out. I tried different fuel tubes, tanks and tank mounting... in the end a pressure chamber on pressure line from exhaust was solution.

finaly got some good weather and all fixed now.ended up with new tank/fuel line new airfilter and a diffrent carb,but could not find any thing wrong with the ones i took off.thanks to everyone for the help...