I have two B&S engines on two different machines A 5hp on y tiller and 8hp on my air compressor And an older 11 hp on an old lawn sweep. Anyhow the newer ones have both decided to surge when at idle. I've cleaned the filters and wanted to try and adjust the carbs. They seem to be running lean. Being old and not seeing that well I can find the adjustment screws on the carbs. I'm pretty sure the 5hp doesnt have any at all. SO what do I look for or whats the solution. They appear to be running lean at idle. The older 11hp has a down draft carb I'd like to replace but with what??