Maiierst. I have Wall 4 that I run a 5' R/C boat that had the same problem. I cleaned it out then took a 1/16 dia. punch and packed teflon tape in, That is tapped it in This was 56 yrs. ago. I have run this boat yr. after yr. Capt,n John has seen a video of it runnig. I have made a number of the 4,s. Casting from Wall Labs,Coles models,when the Cole family still owned the com. It seemed to happen on the number 1 cyl, do to the fact it always looked like that was a vent end and sand would find way to that corner of the pore. Teflon tape was quite new back then, one of my friends gave a roll of it told me what thay used it for, a hole new world.