18.5 hp B&S starts but no high rpms

[slomo]

Can you manipulate the throttle linkage and make it run faster with your fingers? Check for bent linkage and gov maladjusted.

slomo

 

[bertsmobile1]

If it is still apart then take a shot of the governor mechanism
Some of them can pop apart but apart from that I can not think of anything else right now

 

[StarTech]

Governor as it is closing the throttle vane. Throttle linkage is connect to the governor spring and increases the tension on the governor for faster rpms. It sounds like you have the throttle not connected properly; therefore it is increase tension on the governor spring.or you even the linkage connected wrong.