Throttle for FOrster .29?
One last thought. Some non-throttle engines used sub-piston supplementary air induction to increase power. The bottom of the piston skirt would rise above the bottom f the exhaust port at top dead center and allow a little more air to enter into the crankcase. Many of the Cox reed valve engines used this. I had a Super Tigre .23 control line engine that had this porting. When I added a throttle, it would only idle when it was fitted with a muffler which prevented any fresh air from entering the crankcase via the exhaust port. The Super Tigre 23 RC engine did not have sub-piston supplementary air induction and idled well without a muffler. Check to see if the Forster .29 has the sub-piston porting. If it does, then don't waste your time with a throttle.