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exasperated (@#$%) Jett .50 owner

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Old 10-19-2008, 03:09 PM
  #1  
JT Hammer
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Default exasperated (@#$%) Jett .50 owner

I bought my first SJ .50 about a year ago. It continues to perform well. I bought my second just a few weeks ago. I have been breaking it in like the other i.e. 9/7, 9/8 and then to a 10/6 prop with a bit more than a gallon of fuel through it (Omega with the castor mix). My Phoenix F-20 likes this engine and moves well. About 4 flights ago, the engine became hard to start. The last two times out it was very hard to start and wouldn't keep running. I have tried may things in the driveway. I have re-plumbed the tank. It is totally tight and holding pressure. I removed the needle valve assembly from the back of the engine and attached it to the side of the fuse so less fuel line is required. I did remove the needle valve once in order to put it through the cowl hole. According to the intructions this is a no no! I have tried three or four different glow plugs with no difference. Currently I can get it started with difficultly only if the carb is open more than half. Anything less and it stops dead. Whereas before I could thumb choke it and bring fuel to the carb, now the fuel won't draw up. I believe the compression is less than before but not sure about this. I have also played with the idle screw both ways of the starting point position - no luck! When I do get it started in a rich needle valve position the carb must remain half to full open to keep running. When full open and rich the engine is maybe turning 7000 rpms. Turning the needle slowly in only results on a few more rpms and then stops. If I quickly richen the needle before it stops it will contunue running. Continue to richen and it will stop. I have checked head bolts and back bolts and slightly tightened 2 or 3 that needed snugging up. AM I MISSING SOMETHING? I'm thinking I will have to sent this one back to 'Jett'. Mabe I've fried this engine but I can't recall having a very lean run or having the engine getting crackling hot. Ideas/suggestions - welcome!
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Old 10-20-2008, 08:59 AM
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Default RE: exasperated (@#$%) Jett .50 owner

Look at this first before you adjust anything else..... (this is something we have seen in the past a few times)

Did you get the engine hot along the way? A hot/lean run will cause the head bolts to come loose. Usually will blow a plug too.

Remove the muffler - look into the exhaust port. Make sure the sleeve port lines up proprely in the crankcase. They should center left to right (dont worry about up and down).

If you get a hot run the head bolts can/will come loose. If you change the glow plug with the bolts loose, the liner will rotate when you tighten the new glow plug in place. A mis-aligned sleeve will make the engine either not run, or will make it run VERY poorly.

If the sleeve is not lined up, loosen the head clamp bolts (head bolts) put the piston at the bottom of the stroke. Then use a glow plug wrench on the glow plug to turn the sleeve and head button so it lines up properly in the crankcase.

(if this happened, go over the fuel system again - chance are it went way lean in flight - maybe fuel foam - be sure the tank is padded and not touching the airframe)

Sleeve position is ok? Other things to look at ....


Did you adjust the low speed mixture at all? This is not a standard type idle needle valve. It is a mid-range mixture more than anything else. Dub sets this at his shop before the engine ships. If you turned that inward more than about 1/4 turn, it will do exactly what you are describing (It will cut off fuel flow entirely below about 1/2 throttle and can mess up with fuel delivery on the top end too). There are instructions on the website about setting the carb and how to start-over with the low speed mixture. Starting point would be with the low speed mixture screw appx flush with the surface of the nut.

Another possibility - Not running at all or drawing fuel when in low throttle - there is an air leak in the engine. Make sure the backplate screws are all in place and are tight, make sure the head bolts are tight, make sure the carb is fully seated down. Since you can not choke it to draw fuel, please check for these.

More to look at if the above does not work....
You may have an obstruction in the needle valve assembly (dirt, debris) blocking the venturi. Fuel should flow easily through the needle valve. Re-installing the needle to make the installation work well is not a huge problem - others have done this (When that goofs up, you can not lean out the engine usually - needle wont thread in - opposite problem than what you have). Disconnect the feed line to the carb, turn the needle full in, back it out about 3 turns.... blow into the pressure/vent line. Fuel should easily flow. If not, there is an obstruction in the needle/spray bar. Take the remote needle apart and clean it out (Easy to do).


Also...

Once you have checked everything - be sure to remove the engine from the aircraft and mount it on a solid test stand. That is the only place to effectively diagnose an engine issue. Run it there, make sure it runs properly on the bench, make any adjustements needed on the bench. If it runs properly on the bench, this will get you very useful baseline rpm information. Then reinstall in the airframe and run it there - should run identical.

If it does not run properly on the bench under controlled conditions, then it might be worth sending it down for a look-see.

Let me know how you make out.

Bob
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Old 10-20-2008, 12:54 PM
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Default RE: exasperated (@#$%) Jett .50 owner

hey bob...i've played with 2-cy engines for over 50 years (i've never owned a 4-cy - maybe that will be put on my gravestone)...i just wanted to chime in and say that i'm always amazed at your posts - not just what you say (spot-on), but also how you say it (never talk down to us semi-senile guys)...keep it up! you're a great spokesman for jett!
-ken
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Old 10-20-2008, 01:19 PM
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Default RE: exasperated (@#$%) Jett .50 owner

I appreciate the comment and positive feedback.

I learned the same way from folks who were patient and were helpful. Just paying it forward [8D] and trying to give accurate info in the process.
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Old 10-20-2008, 05:30 PM
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Default RE: exasperated (@#$%) Jett .50 owner

Thanks so much for the prompt and excellent reply Bob. You have provided a lot of good information which I am printing for future reference. I removed the engine from the airframe and upon looking in the exhaust port found a liner that appears to be broken on the left side lookin in. At least it feels rough and irregular when felt with the tip of a small screwdriver. It also has a blackened look. The liner may have rotated as well. I wish I could draw a picture here. When looking through the port should one see a narrow vertical part of the liner right in the centre? I wouldn't think so! I have installed a VMAR .46pro in the f-20 for now and it is running ok. Am planning on flying with it tomorrow. I know the take-off run will be longer!! Anyway, I must have gotten the Jett too hot - wow is me (embarrassed too). I will pack it up and send it back to Dubb, who will likely fix it and send it back with some well chosen words. Should I send it back as I received it i.e. does he want the muffler as well?...........Thanks again for your help; much appreciated.

Terry (JT)
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Old 10-20-2008, 06:53 PM
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Default RE: exasperated (@#$%) Jett .50 owner

Further to the above. I may not have to send this engine back. I looked closer through the exhaust port under good light. I don't think the liner is damaged. I loosened the head bolts and rotated the liner back into the correct position so now you see 'just' a rectangular port/hole! Put a prop on and turned the engone over by hand - good compression. The piston also looks good. So, I'm pretty sure it's going to work next time I get to try it. Thx again.

Terry (TJ)
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Old 10-21-2008, 10:36 AM
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Default RE: exasperated (@#$%) Jett .50 owner

Ahh... good deal checking that !

Does sound like it was a liner rotation. Just toss a 9x7 prop on it and run it a time or two. Find peak rpm very briefly, back it down about 1000 rpm and just let it run. Should run properly now.

If its not running, no problem sending it back. Stuff happens, and ARF fuel system installs are not always the best. Yes, you want to include the muffler just so it is complete as a set.

The liner port shapes can appear a bit irregular - not always crisp and clean rectangles or ovals - shaped as they are for a reason.

Let me know how you make out

Bob
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Old 10-23-2008, 05:09 PM
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Default RE: exasperated (@#$%) Jett .50 owner

Good news Bob. After realigning the sleeve, the engine fired right up and ran well. The idle screw needs a bit of tweeking yet. It seems quite critical to get just right. Question - Since the sleeve is realigned basically by the 'eyeball' method, it is likely not exactly aligned to the piston as it was before. Does this mean it needs to be 'run in' as I did when I received it? The weather up here in Canada is starting to get cold. When I flew the F-20 this morning it was -3 degrees. I had installed a VMAX .46 while I tinkered with the Jett. NO COMPARISON!! At least I had a one flight fix. Tomorrow the weather looks a bit better, so with the Jett reinstalled the performance should be improved. One other question. Have you seen that new laser cut kit by AK Models - SIMPLE FLYER? What a unique looking thing. Looks like it might be a mover with a Jett engine. Thanks for all your help.

Terry (JT)
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Old 10-24-2008, 07:28 AM
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Default RE: exasperated (@#$%) Jett .50 owner


ORIGINAL: J.T. Hammer
Have you seen that new laser cut kit by AK Models - SIMPLE FLYER? What a unique looking thing. Looks like it might be a mover with a Jett engine. Thanks for all your help.
Terry (JT)
Looks cool, except the landing gear looks like it's belly was attacked by stick insects. MJD
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Old 10-24-2008, 08:21 AM
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Default RE: exasperated (@#$%) Jett .50 owner

Good to hear it runs ok JT...

As long as the engine is running well, dont worry too much about it. Sleeve is not laser-aligned at the factory or anything like that.
The fit-up will come in just fine with a few flights.

Keep a lighter prop on it to start with (9x7) for the first handful of flights. Then you can move on to a 10x6 or even a 9x8 - the Phx f-20 seems to like the larger diameter sometimes.

The simple flyer is something Alex has had available for a number of years. Its an interesting plane. Never saw one fly though. Might be quick.

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Old 10-24-2008, 05:10 PM
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Default RE: exasperated (@#$%) Jett .50 owner

Well, I made it to the flying field today expecting a good flight. The Jett started ok and would run at close to peak rpms while level on the bench. When held upright it would abrupty stop, even at 45 degrees upright. Richening the highspeed needle wouldn't help. Also tried adjusting the low/mid screw in and out from the starting point (screw even with the nut). I mentioned before that I had removed the main needle from the needle-valve assembly on at least one occassion. Would this have messed up something? One other thing, I noticed when I had loosened the head to realign the sleeve, the small part that the plug is screwed into moves independantly from the rest of the head. You had mentioned to realign the liner you would turn the plug with the plug wrench until liner is in correct position. This didn't work as the plug portion turned but the liner did not. So I did it through the exhaust port using a small scredriver tip. It's almost too cold to fly here now so I have plently of time to send it to Dub if I can't solve the issues here. Thanks for your patience Bob!

Terry (JT)
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Old 10-24-2008, 05:12 PM
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Default RE: exasperated (@#$%) Jett .50 owner

According to RealFlight it goes 400 mph with a large turbine. Of course, a Sleek Streek would go even faster..

It does look interesting, and it seems to have pretty low frontal area. Hmm, fuse top header, pipe tunnel..
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Old 10-25-2008, 07:20 AM
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Default RE: exasperated (@#$%) Jett .50 owner

What is a Sleek Streek?

JT
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Old 10-25-2008, 01:14 PM
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Default RE: exasperated (@#$%) Jett .50 owner

I hope you read this Bob..........LIFE IS GOOD AGAIN!! I thought I'd take another look at the sleeve and exhaust port alignment. I can't believe the boo boo I made. I lined up the incorrect sleeve port with the exhaust (much smaller than the correct one). I feel like putting a sack on my head. The end result, I put the mufffer back on, took it to the driveway and it fired right up, Readjusted the idle/mid range screw and voila - perfect! Good transition to high, excellent top-end, holds in the vertical, etc - everything, lovely. Maybe I can still get out for one more end of season flight!

Terry (JT) (ps I'm surprised it ran at all with the sleeve ports reversed)
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Old 10-25-2008, 01:25 PM
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Default RE: exasperated (@#$%) Jett .50 owner

Sounds like an adventure

But hopefully you can get it out for a flight.

Taking out the needle valve is ok. Usually does cause a problem unless you re-tiighten the packing nut while the needle is removed.
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Old 10-25-2008, 03:19 PM
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Default RE: exasperated (@#$%) Jett .50 owner

Good. I guess we can this discussion - Thx.

Terry (JT)
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