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J600R popping back through compressor on start with gas

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J600R popping back through compressor on start with gas

Old 12-15-2023, 11:02 AM
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Default J600R popping back through compressor on start with gas

I know there are probably not many of these left out there but I have a very low time J600R (fairly new to me) that has an odd start issue. During the start sequence when the start gas is applied, it will pop back with flames through the compressor. It will do this for several start cycles until the engine temp starts to rise after which time it will catch and then proceed on kero normally and take off. Once running, it runs just fine. Subsequent starts are totally normal as long as the engine doesn't cool completely to ambient.
I have checked glow which is fine. Also tried adjusting the temp probe slightly; it is right around 2mm. I normally use PowerMax but also tried straight propane; no difference.
Both Kelly W and Helijet have seen it do this and are also puzzled. If you're still on here guys and want to chime in, feel free.
Not a show stopper but would like to figure this out if possible.
Just wondering if anyone else has seen this and what did you find?
Thanks -Rob-
Old 12-15-2023, 12:54 PM
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Weird, haven’t heard of that before. If the RPM and propane pressure is correct, I wouldn’t have thought propane could easily pop back through the compressor.

Maybe the glow plug isn’t hot enough and the engine is flooding with propane until it finally pops out both ends? Glow plug has the coil “teased” out of the plug? Could bump the voltage a bit or maybe try turning the engine in the mounts in case the propane isn’t reaching the glow plug easily? The manual suggests that can happen and cause problems, though not quite what you mention.


Another thought: Have you checked under the front cover for propane or fuel leaks? I’ve seen a couple of these J600Rs with brittle, powdery plastic fuel lines under the cover…perhaps yours has a cracked propane or fuel line and that’s leaking into the compressor/diffuser area and lighting off the propane?
Could also be a problem with the propane metal tubing, gasket, or nozzle maybe. Harder to check those without disassembly though…
Old 12-15-2023, 01:32 PM
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I have a couple of 600r, great engines. That said, as above do check all your lines under the hood, after 15 years mine were beginning to disintegrate !
Also check you have not cross connected fuel and propane lines !
Both of mine were converted to FADEC. ECUs . Made a lovely little engine even better !
Getting cold in Canada ?
Old 12-15-2023, 09:15 PM
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Originally Posted by David Gladwin
I have a couple of 600r, great engines. That said, as above do check all your lines under the hood, after 15 years mine were beginning to disintegrate !
Also check you have not cross connected fuel and propane lines !
Both of mine were converted to FADEC. ECUs . Made a lovely little engine even better !
Getting cold in Canada ?
Probably is although I happen to be enjoying sunny and warm Southern Arizona for the winter!

I will have a check under the hood and see what I can find. I would think though a leak would cause this issue all the time regardless of prior runs. After the first start this one is fine for the rest of the day which would also rule out cross connected lines as well.
Old 12-15-2023, 09:23 PM
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Originally Posted by darkith
Weird, haven’t heard of that before. If the RPM and propane pressure is correct, I wouldn’t have thought propane could easily pop back through the compressor.

Maybe the glow plug isn’t hot enough and the engine is flooding with propane until it finally pops out both ends? Glow plug has the coil “teased” out of the plug? Could bump the voltage a bit or maybe try turning the engine in the mounts in case the propane isn’t reaching the glow plug easily? The manual suggests that can happen and cause problems, though not quite what you mention.


Another thought: Have you checked under the front cover for propane or fuel leaks? I’ve seen a couple of these J600Rs with brittle, powdery plastic fuel lines under the cover…perhaps yours has a cracked propane or fuel line and that’s leaking into the compressor/diffuser area and lighting off the propane?
Could also be a problem with the propane metal tubing, gasket, or nozzle maybe. Harder to check those without disassembly though…
Nothing happens when the starter is first engaged. It pops back when the starter cycles off. As soon as the starter engages again, it sucks the flame back into the core until the next cycle.
I am not sure how old this one actually is, so will pull the front cover and check the lines as suggested. I'll also check the plug again to be sure.
Old 12-16-2023, 10:00 AM
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So, the pop happens after the first spin, just when the gas is turned on as the RPM is coasting down to 2k, and then the flame gets sucked into the engine when the starter re-engages?

Does it start to gradually heat up from that point on? Or does it do several full spin down, then spin up cycles trying to light the propane?

You mention it takes a couple start cycles to get to kero temp and running, do you mean full “Start failed, engine shuts off, renable start on the TEMS, initiate start again with throttle” cycles?

Any stickiness in the bearings when cold? Was two stroke oil used at any point?
If you try it again, a YouTube video of the behavior and the GDT screen might help explain what you’re seeing…
Old 12-16-2023, 08:42 PM
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Originally Posted by darkith
So, the pop happens after the first spin, just when the gas is turned on as the RPM is coasting down to 2k, and then the flame gets sucked into the engine when the starter re-engages?

Does it start to gradually heat up from that point on? Or does it do several full spin down, then spin up cycles trying to light the propane?

You mention it takes a couple start cycles to get to kero temp and running, do you mean full “Start failed, engine shuts off, renable start on the TEMS, initiate start again with throttle” cycles?

Any stickiness in the bearings when cold? Was two stroke oil used at any point?
If you try it again, a YouTube video of the behavior and the GDT screen might help explain what you’re seeing…
As I recall, yes, the first pop happens on the first spin down and subsequent ones as well. It does gradually heat up and will eventually 'catch' and take off. That usually take 2 or 3 full start/fail cycles.
Bearings to me feel fine. I have only had it for about 1.5 run hours and have always used Jetoil II or Aeroshell 500. Before that I have no idea. Total time now is about 6.5 hours.
Oddly when we test ran it on a test stand before I purchased it, it started and ran just fine. That was only one start though.
Hoping to get out tomorrow morning and if so, will try and get a vid of what is going on.
-Rob-
Old 12-27-2023, 09:07 PM
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Hello Robd, if you haven't already tried, I would replace the glow plug, being sure that sufficient coils are exposed at the plug end, etc. My experience is that for some gas-start turbines, this can be a sensitive area that becomes problematic over time-worth a try regardless

On another note, I owned a PST600 over 20 years ago! My experience with this turbine was positive. The quality was very good for the time and even compares very favourably by todays standards (however spool-up was slow when compared to todays turbines). I can even recall visiting the factory and having the staff run up a turbine on the public side-walk just outside the front door of their retail shop!

Regards, Frank

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