Im not too happy with my STS engine right now. When I had it running before the idle was very inconsistent. At idle it would rev really high like it has at quarter throttle. I knew something wasnt right cause my throttle linkage and idle settings were all correct. It sounded like an air leak. BTW this engine is the 21E with a roto start backplate. Also when I got the engine I never took it apart, i just put a glow plug in and broke it in by the book. Its had less than a 1/2 gallon through it and Ive been really impressed the motor so far. So I took out the engine and found that the backplate was loose, so this explains the air leak. Then I took off the backplate and saw that there was thick grime inside the engine and the crank was rusty, all this caused by the loose backplate. Im just kinda pissed off cause this happened. I mean I never opened up this engine before and I trusted that the factory did a good job tightening the backplate screws enough, apparently not. O well i guees ill have to put some lock tite on the back plate screws and learn from this whole experience.

I do not care what brand engine I get I all ways take the backing plate of seal and lock tight the screws as well as seal the carburetor where it goes into the case. As far as rust are you using after run oil? Do not know much about the E but the STS with a tight pinch are not broke in well or ready to tune for performance till at least a gallon. Matter of fact I have never broke in any big block that ran well till at least a gallon! I have 3 STS engines 2 with 4 or 5 gallons a piece with little or no problems.

can you post a picture of the rusty part? I can't belive that it would start to rust in a short time spand.

and use some red or copper sealent around the backplace to seal it.

Being methanol is so hygroscopic if you where to leave an engine in a high humidity place even over night with out after run oil I do believe you could see some rust. It all so has a lot to do with what fuel you run.

I put the engine back together and now it runs perfect. I guess it was my fault for not tightening those screws down before running the engine. I just hope that everyone would learn from my experience.

I always use after run oil. I run Trinity Platinum 20%, good fuel that Ive never had a problem with. I have no clue why some rust is showing up on the back of the crank. Its probaly from the air coming through the backplate when it wasnt tightened all the way cause I always store the piston at TDC. I think after another half gallon running at high temps the rust should disappear.

you should put the piston at BDC when you are not running it.

Really? People have told me TDC. Why should you keep it at BDC when not running?

well you stop the engine the engine is warm and it exspands when warm so when you stop the engine it cools and when it cools the sleeve srinks a little, but with the piston TDC the sleeve srinks to the piston and can mess up the sleeve and when you put the piston BDC the sleeve can exspand and contract with out messing it up and with out getting out of round and things.

I don't thank I did a vary good job explaining it but you might get what I'm talking about.

I know exactly what your talking about but that really only goes for when your breaking in the engine. After the engine is fully broken in I dont think it really matters where the piston left at while not running.

well maybe not but I hear its a good habit to get into and I see lots of people at my local track always put the piston BDC after every run.

Hope you put some Loctite on the backing plate screws!