GB backplate to tank seal

wha-tah-hey wrote:And a timely lesson - I got 2 eBay product engines yesterday, 1 with a Tee Dee head.
I ran 'em on the bench and the standard head gives ~800 more rpm over the TD on Cox 15%.
Higher nitro might reverse those results but it seems achieving high rpm is a process, not necessarily simple.

What exactly are you using for 15% fuel Terry? The engines will run on that % nitro.. but ideally you want 25%+. You can order it in pints.. direct from Sig Manufacturing Co. up in Iowa. I've had great luck with their "Champion 25 and 35" blends. Don't run just any glow-fuel in your Cox engine. I apologize if that's general knowledge on your part.. or if repeat-discussion.

Variables are plenty.. but make a checklist and keep data of your tweaks/combinations/configurations. You already have various data/trouble-shooting resources to work with. You'll make those engines sing! It's just a matter of experimentation.

Tankless/product engines (like your recent acquisitions) are easier to deal with IMO. They eliminate some variables. You have good compression in both engines. Try swapping plugs.. one might have a better coil/element than the other.. or an insulator/seal leak. Was there more than one head-gasket used on the engine with the Tee Dee head? Just curious. There's usually a reason why someone runs one on a reed-valve engine.. but not necessarily. It could have just been thrown on there to sell it. Maybe try your GB plug in place of it.. and see if there's a marked difference in performance.

The reeds/retainers.............. plenty of discussion to be found here on that. I tend to use a reed that was designed for the retaining-system. Some people thin-out a wire/circlip retainer designed for a .001" thickness (CuBe) reed.. to retain a thicker .005" Mylar reed, whether star-shaped or oblong. It just has to work.. and an easy way to tell.. is to apply the blow/suck method using your mouth over the reed-holder. When blowing (not forcefully) the reed should seal. If air passes or it "squeaks"... check/clean the seat/reed.. refit/re-orient the circlip and try again until a definite open/close action is established. I've found the later Cox "cap-style retainer/Mylar-reed" combination to be much less sensitive to this attention to function.. but whichever; it's basically the heart of the reed-valve engine. Don't ever assume that  a reed is functioning in a "stale" engine. The reed can become stuck to the seat if run.. then left/put-away un-cleaned for a time. A good soak in solvent will loosen it. The copper reeds will deform/crease easily.. so care must be taken if one is stuck-tight.

I'll need to "practice what I preach".. with Ron Cribbs coming up to RI early next month!