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Kraft(RJL) engine problem

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Kraft(RJL) engine problem

Old 09-07-2014, 08:39 AM
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Default Kraft(RJL) engine problem

I have a running problem with an old Kraft 61 engine (later RJL) that I can't solve. If it is adjusted by the pinch method it blubbers rich at full throttle but if it is leaned out it has no power. If you can take off with it running rich (very low power) it unloads in the air and runs strong. Running full throttle on the ground if you pinch the fuel line it leans out and runs strong until you throttle it down and then run it back up. I have tried different tanks and tank heights. I have tried every glow plug heat range. I installed a new carb from MECOA. I have run 10 and 15% fuel. I have tried it with and without muffler pressure. It runs well on the low end and has a good idle. It has good compression. I also disassembled it, cleaned it and installed new bearings. Does anyone have experience with this engine? I hate to give up on it because it is such a strong runner when it runs.
Old 09-07-2014, 09:12 AM
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I had one wayyyyyy back in '84. I did change over to a OS carb even before running it. I have very fond memories of that engine as it always ran perfect. It was mounted in a GMP Competitor heli and always run on K&B 100 fuel ( castor based 5% nitro ).

Based on what I have read it appears it is having what I call a thermal runaway. What causes this is usually too much nitro for the compression ratio. If I was standing where you are, I would switch out to 5% nitro and install an OS# 3 or Enya # 4 plug. The other option would be to stick with the fuel you have and add an additional head gasket.

needless to,say this is dependent on everything else being in good working order. Old fuel that has been stored in a container not 100% sealed could have enough moisture content to cause issues described.
Old 09-07-2014, 10:05 AM
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I have thought about the nitro content. I'll try to find some 5%. Why did you change the carb from the get go?
Old 09-07-2014, 05:13 PM
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I happened to have an OS 2B carb and it was a drop in so I dropped it in. LOL. I honestly have no idea how well the factory carb would have worked.
Old 07-02-2016, 07:04 AM
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I am bringing this back because I finally solved the problem. After a long wait I received a new piston ring and bearings from MECOA. I had the plastic back plate sealed with silicon and resealed the same way. I rebuilt the engine and tested it yesterday. After breaking it in and leaning it out it runs great and doesn't exhibit any of the problems I was having with it. It has good transition and runs strong. I don't know if it was low compression or crankcase pressure that was causing the problem. I would like to hear anyone's thoughts on this.

Last edited by ochsnm00; 07-02-2016 at 12:31 PM.
Old 07-04-2016, 06:10 AM
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I would go with the crankcase leak as having been the problem.
Old 07-11-2016, 08:17 PM
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I'm still running a 35 year old Kraft 61 built before RJL took over production. It has had one rebuild and that was needed probably because of using high castor fuel in it's early days. The Dykes ring seems to do better with a good castor/synthetic fuel to keep the carbon build-up from forming. It has the original Kraft carb on it and I seem to notice that it likes to have the low end needle tweaked to near perfection to get the power up where it is best. Can't complain about the service life of this one.

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