I think a better solution would be to have Henry (himself) drill and tap your head button. The charge is fairly nominal - Around $20 including a few glow plugs. You also need to run more nitro, around 25% to get the NorVels to crank up.

Email Henry- -     nelcomp (at) fyi (dot) net

IMO, just from my trials, which have been many, not much difference in performance between 20 or 25 % nitro and 35%, 35 just burns out more glo plugs. Nelson and TeeDee (head), plugs are as close as you will get to the factory Norvel plugs, which in my opinion are great. Most aftermarket glo plug and head set ups suffer a loss of compression, which on a Norvel equals loss of performance as they like to rev high. If you tap a head try to keep the space inside the plug as close to the original as possible. I have tried several aftermarkets and the engines will not run well unless the original compression is saved!! I only have one of the .074 heli converted engines and it does not rev as i think it should, but my neighbor (Nascar engineer) lapped the piston because he thought it was too tight at the top!! I had left it with him one day to help make motor mounts and when i came home he had broke in the engine for me!! I too think the venturi size is very small on this motor, maybe my next adventure with this engine will be to enlarge the venturi. For my thinking venturi size is all trial and what works, right now i am trying different venturi size on .061 Norvels, so far the smaller venturi on the car engines gives more rpm's and will rev with the ame's and their larger venturi's. Just getting started on this quest myself, please post if you come across any anwers or solutions,    Ray