tuning a 305 on propane arrgh

so here's the kick in the butte i go and rebuild the top end on my 305 you know the cam and the fun stuff in life and i am running this old 77 chevy silverado on propane and now tuning the thing has been the biggest pain the rear axle... the ??? is what am i to different when tuning propane instead of gas i cant seem to get the timing to set just right like i had it set before the top end was rebuilt. the truck has been on propane since i bought it for $400.00 cheap little turn key operation that it was hehehe

Thank guys that help about as much as kick the wazoos hahahaha

Kick up the timing, check the plugs and that should help.

Thanks guys the timing issue is going to be a bit of issue i think until i get the propane system as a result since of the tinkering, i posted today.