Okay To Run A Stock Cylinder With Modified Head?

Recently, I had Eric bore and port my 91 RM 250's cylinder - for pump gas. After two rides, I blew it up again - lean condition. I have a big hunk of Nikasil missing from the cylinder wall. Until I can get the cylinder replated, I was wondering if I could run a stock cylinder with Eric's modified head?

Eric: I will send the piston with the cylinder. I haven't found the lean problem yet. The first outing after the mod was installed, the thing ran great. In fact after the Break-In Period, it seemed to be running a little fat on the bottom. I raised the needle up a notch - it ran great after that. After the change, I got the bike wide-open - killed it - and check the plug. No sign of a lean condition. Two weeks later I went back to the same place - used the same gas, same oil, and same ratio. The bike fired right and seemed to be running great. Went for a long ride and noticed when I stopped it was acting like it was running out of fuel (ying - ying - ying). As I was heading back to camp, it started bogging. I replaced the Main Jet with the next size up and fired it up. It seemed to be running better. I decided to go on a little test ride - I never made it back... I should also mention that at the same time I put the modified cylinder on, I also installed a V-Force Reed Block...

I also used a gasket. The boot itself is in good shape - even being more that eleven years-old. I know because I had to modify for the V-Force to work...