ORIGINAL: lbarnes
WOW, DANGER DANGER information overload
Really, thanks for all the info. My first try with the pipe I destroyed 3 plugs. The engine was just getting hot and could not richen it up. But that was at 9.5" from the plug. After I lengthened the pipe the temps went down, plugs survived and started working on trying to get it tuned.
One thing that bothers me is at open throttle I can open the needle valve as many as 6 turns (almost out of threads) and I cannot get it to blubber. At first I thought my tank was not presurized but I did confirm this by taking the pressure line off the tank at full throttle and placeing it in a glass of water, lots of bubbles.
Larry,
Its a learning experieince isnt it
As I noted, when the pipe is set too short, the engine will not run properly and will be hard to needle.
Also, rpm expectations have to be realistic with regard to the engine you are using.
Of note, blowing glow plugs, 96% of the time, is due to one thing - a LEAN mixture setting - and nothing else. A short pipe can drive a mixture lean as the engine attempts (and fails) to stage up on the pipe, but does not have the fuel delivery.
When setting your mixture for flight (with a pipe) always back off at least 500-700 rpm - the engine will need the extra fuel in the air.
BTW... RPMs we are talking about with your .46 size engine and the 9" props are well within its capabilities... it will not shorten the life of the engine or cause a failure. The only real wasy to destroy the engine is to use unsuitable fuel (too little oil) and 'over prop' it and/or run it lean (get it hot).
Bob