Hello,
Jett 60 with Windy's carbon composite pipe in my Intrepid XL runs very well on the ground.
The engine is easy to start and holds the launch RPM well.

Details: 10% nitromethane fuel with 22% synthetic and castor mixture. 12.5 x 4 wooden two blade Zinger propeller ( cut from 14x4 to obtain wider blades), pipe's baffle is 17.75" from the Thunderbolt 4 cycle glow plug, black Teflon Jett venturi drilled to dia=0.225" ( from 0.185") and fuel delivery hole drilled to dia=0.100" ( from 0.060").

In September of 2014, this engine received a new RoJett piston and liner without any modifications to the ports and has been bench run for about 30 minutes. Then, the engine has been carefully checked and cleaned, properly protected using the after run oil and stored for the winter. I have checked the engine again for the presence of rust before mounting it to the model and started flying at the beginning of May 2015.

Tank: stunt style, metal, 6.25 fluid oz., probably from Brodak ( I got it from Windy ). The tank is placed properly w/r to the venturi spray bar level.
Fuel and air filter are installed.
Pipe's short stinger has the silicone exhaust deflector leading to ~ 10" long aluminum tube ( cross section area =0.100 square inches ). This tube directs the smoke away from the fuselage and tail surfaces that remain almost completely oil free after flight.

Comment: my Intrepid needed some tail weight and the exhaust aluminum tube provided such weight. I have not noticed any detrimental effects of such tube. Specifically, there is no engine overheating and no decrease in ground RPM.

Engine and engine header have enough cooling and the entire system has no visible leaks.

The launch RPM yesterday were: 9,200, 8,800 and 8,500 respectively ( maximum ground RPM is ~9,600 with the fuel/ prop/ venturi setup described above )
In each case and shortly after take off, the engine increased the RPM in level flight on 66' lines (from the handle to the model COM) resulting, in each case, with the model flying too fast with the engine in 2 cycle mode for about three minutes ( 4.7, 4.9 and 5.0 seconds per lap). After that, the in flight RPM were going smoothly down and the rest of the flights ( about 5 minutes ) was acceptable with lap times 5.1. 5.3 and 5.5). During first three minutes of each flight there was no audible change in RPM while doing wingovers.  After that, I could hear the engine increasing the RPM while flying up and decreasing the RPM while flying down.

Can the engine behavior in the first three minutes of each flight be attributed to the fact that the break-in process is not finished yet?
Is it possible that the liner needed these three minutes to expand properly and only after that time the compression became "soft" enough for the system to reach the 4-2-4 break while doing wingovers?

Your comments and suggestions are appreciated,
Matt

P.S: please note that the maximum ground RPM for this engine setup is 9,600. I could not reach 10,000 RPM ( ref: Randy's tabulated engines/pipes/prop data ) using the wide blade propeller described above.   

   

Just saw this, one other thing to check is the pipe tuning, you are not tuned at all those RPMs, and most likley the pipe is set wrong at all of the RPMs listed, you need to first off check the exhaust timing on the engine... then set the pipe up per the  chart..

let us know how it goes

Randy