Robin Do you or someone you know have lathe?

The easy way to block the boost port is to turn a plug from a good machinable plastic...Nylon, Delrin or Teflon. Give it a light coat of some sort of oil or grease, mix up the JB Weld and apply same into the boost port cavity. Then slide the plug in to form the epoxy to fit with the liner. All you really need to do is block off the entrance to the boost port, not the entire cavity, but whatever happens is fine. After the JB Weld (or similar) has setup, then the plug can be removed. A little cleanup may be required, but it's not a big deal. Don't leave any little protrusions that could break off, tho.

I've been told you can do this with the cylinder liner, but I'd be afraid of gluing it in permanently. Actually, applying a heat gun to the outside of the case should pop the JB Weld loose, so any of this can be returned to stock. The Magnum XLS .36 I'm running (in stock condition) once had the JB Weld treatment.  Another approach is to carve a small block of soft balsa to fit, and let the fuel/oil swell it to a tight fit.  Steve

So which port do you plug?  This is an FP40 I presume.

I used to do a similar process on OS Max III 15's.  I would fill the entire bypass with epoxy and use a cardboard tube wrapped in wax paper to hold the inbside form.  (I don't have a lathe, either).  The cardboard was from a manila file folder.  It was coiled tightly and inserted, then nature took its course and the tube sprang back to a tight fit.  Not exactly "tool accuracy", but it worked.

The final step was to Dremel out the bypass to the shape I really wanted.

I use a socket from a wrench set wrapped with plastic electrical tape, warm up the case so the JB weld will run to the top of the boost port as it sets. Does require a bit of trimming to get the sleeve to slide in. I did a Tower 40 and noticed that the boost port had a very small duration so I did not block the boost port and it runs really good. I think a far more critical item is the timing of the exhaust and bypass ports. I set the exhaust to 140 degrees and the bypasses to 126 degrees. On the typical 40 that puts the bypasses ~ .035" below the exhaust. The typical OS 40 FP required one to cut about .007 or .008 from the bottom of the liner flange, the Tower was real close to 140 stock, only needed the bypasses raised.
Don