Tillotson carb adjustment

[4speedfury]

Can someone tell me how to set the Tillotson model CO7b Carburetor 1976 10 HP? I only see one adjustment screw. This is what it is doing. If I Idle it, it runs good. It will surge at full throttle. But if I give it a bit of choke, It gains power noticeably. Seems lean to me. Please also note that I am having an issue with crankcase sealing. see crankcase sealing thread... (permatex 51813 will not harden)
Thanks!

 

[Nate3172]

Re: Tillotson carb adjustment

Mixture screws on carburetors are only effective on the idle circuit of the carburetor. the second you crack the throttle off idle the mixture is then controlled by the main jet in the carb only. If you are getting a surge in power when off the idle circuit and engaging the choke, then the carb is running lean and you need to richen it up. It may have some foriegn material in the bowl clogging the orifaces of the carb. try cleaning it first. If still have an issue you may have to jump up in jet size. Getting a "read" off your spark plugs is the best way to tune your engine for air to fuel ratio.