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All Forums >> Glow Engines, Gas Engines, Fuel & Mfg Support Forums >> Engine Manufacturers Direct Support Forum >> Jett Engineering Support >> sj .90l transiton
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sj .90l transiton - 9/13/2005 5:25:00 PM   
ampa


 

Posts: 181
Joined: 7/6/2004
From: torino, ITALY
Status: offline 		dear sir :my SJ .90l idles well but the transiton is far from sharp, these happens specially when the engine idles for more than 5/7 seconds( if from top end I reduce to idle and immediately go back to top end the transition is good), when the engine is left to idle and I keep the nose of the model up the idle tend to reduce even more , that means that the idle needle is too lean?, another problem is that in flight the engine stops when at idle negative g are applied (outside loop)
       Post #: 1

RE: sj .90l transiton - 9/14/2005 2:49:20 PM   
bob27s



Posts: 4730
Joined: 4/9/2002
From: Cleveland, OH, USA
Status: offline 		Hi,

Thanks for writing.

Tell me a bit more about the aircraft, fuel you are using. That can help.

There are a few other posts in here and in the Extreme speed forum on idle and transition on the SJ-90L engine that may be helpful, but here is some basic info.

The idle mixture may be a tiny bit too lean from what you decribed. Back it out a TINY bit and see how things go.

Glow plug selection is important for good transition. The engine is set up to run a bit rich in the midrange to accomodate the staging/destaging of the pipe/muffler without the risk of blowing the plug in midrange coming off the pipe.

The 90L requires a HOT glow plug. Rossi 2,3 work fairly well. McCoy MC-59 is good. The OS-F plug works very well (yes, the 4-cycle plug).

With one of those plugs installed, you can adjust the idle mixture a bit to find the best mixture for your use. Only move that idle needle no more than 1/8 turn from where it was positioned when you received it from Jett.

Engine dying at idle with negative G - that is more of a fuel delivery and a fuel system issue. One suggestion - after getting the plug and transition worked out per above, try installing a small (leak free type) fuel filter in-line between the needle valve and the carb. One of the Jett filters or a Sullivan crap-trap work well. Do some ground runs with this, make sure the filter does not trap an air bubble. This is something I have experimented with a bit this summer on another engine. The filter serves as a tiny 'hopper' tank to keep fuel in the line during extream manuvering.

Previously my mini-hopper concept has worked just fine installing the filter just before the needle valve in the supply line. This approach putting the filter between the remote needle valve and the carb is something sorta new. So far my results have been promising, but if you decide try this, proceed with a bit of caution - develop some confidence in the system.

Let me know how things work out for you.

Bob Brassell



_____________________________

Bob Brassell
Jett Engineering - Engine Mfg Support Forum Host

(in reply to ampa)
       Post #: 2

RE: sj .90l transiton - 9/17/2005 3:10:17 PM   
ampa


 

Posts: 181
Joined: 7/6/2004
From: torino, ITALY
Status: offline 		the model is a 3.8 kg pattern, fuel are about 20% oil and 5% nitro; about the stopping at negative g,I use a two lines fuel tank with the second line that are a brass tube pointng to the top of the fuel tank linked to the muffler pressure, when i pull negative g and cut the engine the tank is inflated by the pressure and the fuel is forced via the pressure line to flood the muffler can these stop the engine? enya 3 is a good plug?

(in reply to bob27s)
       Post #: 3

RE: sj .90l transiton - 9/17/2005 10:55:34 PM   
bob27s



Posts: 4730
Joined: 4/9/2002
From: Cleveland, OH, USA
Status: offline 		Sounds like you have a conventional fuel tank with one feed line and one vent line, pressurised muffler. No problem there. Same as for any other engine. As with most engine and fuel tank setups, there should not be a larger amount of backflow into the muffler while it is running.

One thing that can take any issues with the fuel system compeltely out of the picture, is to use a Tetra bubble-free tank in your plane. They may a very nice 500cc tank that usually works well with the 90L. No chance for fuel and air to mix, no bubbles, no issues at any time with fuel draw or fuel flow.

The Enya 3 is fairly hot. That should work fairly well. But with all other things being equal, it would be a good idea to try the OS-F plug or another similar plug. On 5% nitro with heavy oil (20%) there may be need to get something in there that can handle that situation. Other option is a good idle-bar type (r/c type) glow plug.

Bob




_____________________________

Bob Brassell
Jett Engineering - Engine Mfg Support Forum Host

(in reply to ampa)
       Post #: 4

RE: sj .90l transiton - 9/18/2005 2:07:59 PM   
ampa


 

Posts: 181
Joined: 7/6/2004
From: torino, ITALY
Status: offline 		after i read your first answer I cheked the plug (mc 59): the coil was in bad conditions(squeezed), can these explain the problems?

(in reply to bob27s)
       Post #: 5

RE: sj .90l transiton - 9/19/2005 2:50:40 PM   
bob27s



Posts: 4730
Joined: 4/9/2002
From: Cleveland, OH, USA
Status: offline 		definately - a bad plug will drive you nuts.

Bob


_____________________________

Bob Brassell
Jett Engineering - Engine Mfg Support Forum Host

(in reply to ampa)
       Post #: 6

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All Forums >> Glow Engines, Gas Engines, Fuel & Mfg Support Forums >> Engine Manufacturers Direct Support Forum >> Jett Engineering Support >> sj .90l transiton
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