Oh and what would you say to use, mineral oil? Like the stuff u get from the drug store??
Ha, yeah I suppose drug store mineral oil should be fine. I'd use ATF it it were mine.
I think the issue is you don't want something that will absorb moisture like brake fluid and you don't want something that might eat swell the rubber seals like brake fluid might.
If the viscosity is too high, the action might be lethargic.
And yes, I believe you correctly described the purpose of the schraeder valve. For if the schraeder was installed backwards, pressure created by the throttle actuator would push fluid back into the reservoir thus the throttle actuator piston at the carburetor would not move, or only briefely.
For instance, if you find while operating the throttle while riding your engine speed keeps falling as if the throttle is being released, the schraeder might be leaking, allowing line pressure to bleed off into the reservoir.
I would begin the air bleeding process by removing the schraeder, install the reservoir as normal, install the bleeder plug(s) and fill the reservoir with fluid. It will be important to keep the level of fluid in the reservoir from falling to the bottom, this keeps air from entering the tubing.
Then begin actuating the hand throttle, expect this to force air up and out of the reservoir, then as you release the throttle fluid from the reservoir will displace that air. Maintain the reservoir fluid level from becoming low while doing this and pump the control until air bubbles are no longer bubbling up into the reservoir.
Then, you may remove the bleeder plug(s) one at a time, while maintaining the reservoir fluid level, and allow any further trapped air to escape from the open bleeder plugs. Careful not to induce air, keep the position of the bleeder plugs below the level of the reservoir, while fluid runs downhill inside the tubing to displace trapped air. Replace bleeder plugs.
Finally, if you're convinced the trapped air has been displaced by the fluid and see no bubbles rising up inside the reservoir while pumping the control, remove the reservoir and install the schraeder, then install and fill the reservoir so air cannot enter down into the tubing.
At this point you should have a functioning hydraulic throttle.
There's other ways to do this but this should be an effective method for purging the trapped air with fluid.
