Help with LPG convertor!

[Strick-9]

I need some help from someone with some experience with a liquid propane system.

I've built 4 different vapor propane systems so I'm not starting from scratch.

I got tired of the inconsistency of the vapor systems and decided to go the liquid route.

I need to know what size line others are running from the convertor to the intake.

Apparently, I don't have enough intake vaccuum to open the convertor. I built an adjustable bracket to push the manual override button on the convertor, but then I lose the ability to run more propane with more boost. I'm stuck at a constant level.
I either get detonation at low rpms or weak high rpm performance.

I'm running #4 line to the intake screwed into the clean side of the stock airbox. I'm pulling my filterminder down 1/2 way, so I know there's vaccuum.

My propane powered forklift uses 3/8 line to the intake and that appears to be the only difference from my setup.

I'm guessing that the line is too small to flow the propane while maintaining enough vaccuum to keep the convertor open.

I thought I would ask the experts before drilling into my airbox anymore.

Thanks
Chris