Q-500 Racing Discuss AMA 428, AMA 424, and any other variants of Quickie 500 racing

Jett .46 problem, question

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Old 12-29-2015, 10:51 AM
  #1  
308jockey
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Afternoon all:

Here is a question about a problem with a Jett ,46 engine. I've been doing some work with a group using a Jett .46 engine on a wieght lift project. The engine runs beautifully and pulls some amazing weight but has an odd problem. It will run up to top rpm very well but if it is pulled back to the mid range it will not throttle back up to full power, it simply runs at partial power on the very rich side even with the throttle opened to full correctly. It will quit completely in a fairly short time. This is causing all kinds of problems in flight maintaining proper speed and altitude. Any idea why the engine is running this way? What can be done to make it run correctly at any throttle setting? It is using proper fuel, prop and plug, the needle is set correctly and when it hits top speed it puts out tremendous power. We just need it to get through a complete flight with the throttle at any setting. We have many years of experience but this one has been a mystery. Any help or advice is appreciated. Thanks.

Rick H.
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Old 03-24-2016, 07:11 AM
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I would try a hotter plug.
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Old 03-24-2016, 07:45 AM
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what carb is on it? If it's the sport-jett carb, perhaps the low speed needle isn't right, too.
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Old 05-24-2016, 08:59 AM
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what prop and so on need more info, I bet you are way to lean and the reason its quitting on you.
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Old 05-26-2016, 06:39 AM
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As Dub states on his website, most of the problems with engines that are returned to him turn out to be tank problems rather than engine problems. In an SAE or AIAA heavy lift competition aircraft, the students FREQUENTLY place the tank as an afterthought. Here at FW Thunderbirds, when we do the inspections for the SAE competition, it is frightening to see what some of the students do. If you are not already using a bubble-less tank (Jett or Tetra) then GET one. Also, check for pin-hole leaks in the tank, tank liner and fuel lines. Make sure that the centerline of the tank is approximately 3/8" above the venturi. While these suggestions may not cure your problem, they will certainly prevent others. Trouble shooting engine problems is always difficult. While it may not apply to the .46, we have to set the Q-40 engines off pretty rich, WAY below peak. They heat up and lean out when airborne. We have also found out that the technique of peaking them out on the ground to full lean and then backing them off, causes the engines to overheat and have erratic runs. It is best to simply run them up from rich to a pre-determined rpm and avoid the pre-heating.
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