I had an ASP 4 stroke 70 once. I had many issues with the idle and acceleration. It took a very long time to break in and get it going. Now I don't use the engine anymore. I have an O.S 55 AX and I have to say I have never seen an engine work better than this one. The idle is a little high but break in was easy and I never had to change the mixture control valve. I am now ordering an O.S 120 Pumped. I have read many reviews and this engine sounds great. Idles are very low and break in is not a problem. I am using this engine on a Top Flight P40 so I want the best idle possible.