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Jett 50 problem

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Old 05-31-2010, 08:19 AM
  #1  
Wingspam
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Default Jett 50 problem

i have a fairly new Jett 50, it has about 10 or 12 flights on it. The first 5 to 6 flights where very good ran strong no hesitation, these last several flights have been fairly poor. After starting the motor and taxing out it seems to load up and on a couple of occasions it boggs and sputters so bad I abort the take off. The last 3 successful flights still have a bogg down or hesitaion in flight sometimes it happens just once other flights in happens the whole flight.
So far I have moved the needle valve off the back of the motor( no change), I put all new fuel lines in yesterday (no change), I have very slightly leaned the low end ( no change).

On the bench I am hitting 14,800 turning a 10x8(make that a 10x6) 2 blade pusher prop using the power master 15%. I have this motor on a Nitro models Bobcat. The tank faces forward like in a regular plane so it has long fuel lines

I am out of idea's , help if you can...
Thanks
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Old 05-31-2010, 08:52 AM
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summerwind
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Default RE: Jett 50 problem

you probably already did, but is the plug new?

also, what peak RPM will it hit on the ground?
i remember Bob saying the 50 needs to hit around 16,500 peak on the ground, then backed off so it will get on the pipe and transistion and run properly.
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Old 05-31-2010, 09:11 AM
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jay1st
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Default RE: Jett 50 problem

Did you try cleaning the NV ?
Sometimes gunk will get trapped in there, just unscrew it all the way and blow some air (w/o the fuel lines of course).
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Old 05-31-2010, 05:45 PM
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Wingspam
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Default RE: Jett 50 problem

I did put a new plug in it last weekend, didnt think about blowing thru the needle valve since it is such a new motor... will try that in a day or 2

As far as RPM's, I am hitting 14800 on the flight stand..
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Old 05-31-2010, 05:49 PM
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Default RE: Jett 50 problem

I am wrong on the prop, It has a 10x6 apc prop turning 14800 on the flight stand..
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Old 06-01-2010, 02:03 PM
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Default RE: Jett 50 problem


Wingspam:

You sure have something screwed up here. Being a long time lover of the Jet engines, I have never seen their equal with respects to throttle transition, and solid idle. Gotta almost beat mine to make them stop. If you have checked your fuel system and have the needle nut tight, get your torque wrench out. Don't have one, woops, you can not survive with out a decent torque wrench. Buy one. I know someone will chime in here and say they have been in the hobby since JC, and never owned one. I had the same attitude for years until I stripped a head bolt on my beloved 35.

One day after a club race I wanted to change a plug cause things did not "sound right". Kept turning the plug wrench and nothing was happening. The insert button was turning like it was designed to. Nice and smoothly. Had to take things apart to get the sleeve back into place. These engines are that well machined, like a watch, a rollex at that.


Take your head and muffler off, and check your sleeve. Bet its off a little, and that is all it takes to goof things up. Get the sides equal and carefully torque it down in the intended pattern. Both my 50's and 60's need their heads torqued about every 3-4 runs, minimum. Be sure to check the carb and see if it is pushed into the "O" ring properly. Check the rear case O ring for any damage, any small cuts etc., get a new one.

Both Bob's 27 and Dub have instructed me in the past to move the needle valve from the engine case to the airframe when I was having a problem with a 60. It worked, no more bubbles.

If the above has failed, box that engine up and send it back to Dub Jett. He will get her running rignt at a very reasonable price. His service has got to be the best and most reasonable in the world. For what its worth, I run 15% Power Master fuel with a extra 1 oz of quality castor so I can also use it in my 4 stroke YS 63, 90, 110. The Jett engines seem to like this a lot. I do what ever these little guys seem to like, a happy engine is a fast engine. ENJOY
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Old 06-01-2010, 03:16 PM
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Default RE: Jett 50 problem

agree with Rich.........with a 10x6 you should be hitting somewhere around 16-16,500 easily.
i don't own a torque wrench and i like the idea of using one, but i never run engines lean so haven't had anything loosen up.....might even say my pattern of mechanical setup and checking is rather boring, but competition teaches you that. but like Rich said, if you have run lean and the holdown screws have loosened enough to allow the sleeve to rotate, then that will make a sudden change like you just experienced.

here is a picture of where i have my needle mounted. 6 flights so far and haven't touched a thing, but the 50 is showing signs of more power, not less. i'm still on the original plug too, and that includes 40 minutes of breakin.
these engines are the smoothest and most consistent engines i've run yet.
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Old 06-01-2010, 06:25 PM
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Default RE: Jett 50 problem

I see a three bladed prop in that picture - what are you actually flying it with? It could explain a few things. Overloaded pusher engine, feelin' "hot hot hot", loosened head bolts, plug change, rotated sleeve... ? That situation has been documented here more than once.

If that is a 10-8 3 blader, especially on a pusher setup, it should be on a sport timed .60, not this engine. Heed Jett's instructions about rpm!!! Let it spin!!! I would not put more than a 10-6 2 blade on an SJ .50. Normal advice in the RC fraternity is to reduce prop load a touch on pushers, two strokes run hotter the more you load them up, especially when you exceed a critical threshold defined by the design of the engine and pipe tuning. In general overpropping a 2 stroke is cruel, not kind. Esp a new one, and double-esp if you are overloading it on a tuned exhaust setup.

Bob will undoubtedly arrive here and clear this up. I bet $5.43 on an overheated engine and rotated sleeve or some heat related issue. Search this forum for rotated sleeve and I bet you find some insight. If I am out to lunch here I owe you $5.43.

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Old 06-01-2010, 08:34 PM
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Default RE: Jett 50 problem

The picture is just that a picture, its just there to let people know what plane it is on. I am using a 2 blade 10x6 apc prop........
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Old 06-01-2010, 08:47 PM
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Default RE: Jett 50 problem

First question, have you had a lean run at all? Blown a plug? Sometimes when these engines get hot, the head bolts will loosen up just enough to let the head plug turn when you tighten down the glow plug. That in turn, turns the sleeve and then it doesn't line up properly with the ports. The easiest way to check it is to remove the muffler and look into exhaust port. The opening in the sleeve should be dead center in the hole. If it isn't, you will have reduced performance. That may explain your low rpm readings.

Hope this helps.

Blessings, Terry
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Old 06-01-2010, 09:04 PM
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Default RE: Jett 50 problem

I don't believe I have had a lean run, unless it leaned out too much in the air. On the flight stand once I pass the half way point on the throttle there is a trail of exhaust like you would not believe...I will pull off the muffler tomorrow and check the port opening. I am on my second plug, the first plug lasted for the entire break-in on the test stand and 2 flights before I replaced it.
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Old 06-02-2010, 11:40 AM
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Default RE: Jett 50 problem

Okay, good. The pic and mention of a 10-8 had me concerned so I chimed in about overpropping. 14 and change with that 10-6 is most definitely an eyebrow raiser. Hope it is as simple as a rotated sleeve or the like, as I mentioned there are historical accounts of that here. I wonder if first flights as a pusher is an issue. In the end.. Bob Brassell or Dub will know.
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Old 06-02-2010, 04:25 PM
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Default RE: Jett 50 problem


ORIGINAL: MJD

Okay, good. The pic and mention of a 10-8 had me concerned so I chimed in about overpropping. 14 and change with that 10-6 is most definitely an eyebrow raiser. Hope it is as simple as a rotated sleeve or the like, as I mentioned there are historical accounts of that here. I wonder if first flights as a pusher is an issue. In the end.. Bob Brassell or Dub will know.
read post #5
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Old 06-02-2010, 07:20 PM
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Default RE: Jett 50 problem

I did, that is on the test stand, and I see that it was a 10-6 APC. But I wondered about what was used in flight since (a) I saw a three blade prop in the pic, and (b) read post #1 which mentioned a 10-8 pusher prop, and wondered if putting 2+2 together meant it was flown with a 10-8 pusher prop or worse yet a 10-8 3-blade pusher prop for the first flights.. either of which would lead me to think it might have ran hot on those flights.
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Old 06-03-2010, 08:36 AM
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Default RE: Jett 50 problem

cornfusing eh?
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Old 06-05-2010, 09:06 AM
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Default RE: Jett 50 problem

Ok guys I just pulled the muffler, it does not appear that the liner has moved. The entire opening is clear.
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Old 06-05-2010, 09:58 AM
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Default RE: Jett 50 problem

I think that you should be looking for a higher peak ground rpm.
I do not think that the motor gets onto the pipe until around 14k rpm.
I have 2 SJ60lx's and I run 9x8 apc @ 18k rpm peak ground and when they unload in the air it is awesome the power that they have.
So it maybe that it is loading up with fuel and not using it for energy which would account for the sputtering(excessive fuel)

Or you could do what Bob would suggests; Put the engine on a test stand, eliminate all fuel foaming, isolate the mixture valve.
Start with a rich mixture setting 5 turns out and tune from there, find peak rpm and lower it by 500 -800 rpm.
Go fly
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Old 06-05-2010, 10:03 AM
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Default RE: Jett 50 problem

Sorry I forgot

RPM,RPM RPM these engines like RPM[8D]
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Old 06-05-2010, 02:38 PM
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Default RE: Jett 50 problem

Could the longer fuel lines be an issue? they are almost full lenght out of the package. Would going to a larger diameter fuel line help? from the tank to the needle?

Just another thought I had.
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Old 06-05-2010, 05:10 PM
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Default RE: Jett 50 problem

You need to get the rpm up these are hi rpm hi output motors.
They start cranking at 15k rpm.
Get the prop size down, rpm up and feed it fuel.
You could have 3 feet of fuel line and it would not matter.
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Old 06-16-2010, 10:36 PM
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Default RE: Jett 50 problem

hey Wing,
you ever get this sorted?
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Old 06-17-2010, 07:42 PM
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Default RE: Jett 50 problem

My SJ50 winds up to 18,300 rpm on the test stand. I back off 500-600 from that. The Jetts are amazing!

For these best of engines, Jett of course, why not spend the $99 for an excellent torque wrench?
I got mine from Darrol Cady. He offers an excellent one, and has various props that will help.
Here's his web address:

http://www.darrolcady.com/index.htm

Look over his site, and call or email him. I wasn't sorry after I did.
BillO
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Old 06-30-2010, 08:44 AM
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Default RE: Jett 50 problem

Bill,

Just wanted to follow up ..... Seems like you have most of this sorted out.

Anything new to share?

Bob
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Old 11-08-2010, 09:21 AM
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Default RE: Jett 50 problem

Hey Summerwind
I did get the problem sorted out with my Jett 50, I took it off the bobcat and put it on my well used Hanger 9 F-22, and what a change. It is definately a lot happier in a tractor config. Maybe cooling was a problem when I was using it on the other plane.
It runs very well now no engine bog as it's flying around. Even tho the F-22 is not speed demon with this motor, it has been clocked at 105 with the wind and a consistent 95-97 into the wind. If it wasn't for the fake air intakes acting like an air break I believe this thing would really scoot..

Thanks to everyone for your assistance..
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