Jett 50 possible lean run problems.  
View related threads: (in this forum | in all forums)

Tower Hobbies
Enter up to 4 keywords or Tower stock numbers
Logged in as Guest



Users viewing this topic: none
  Printable Version
       


O.S. Engines O.S. BGX-1 3500 w/ BCM #4224 Pitt
Seller:  jmhernan
Details:   $200.00   |  10/2/2008   |  Classified Ad
We will rotate YOUR AD in this spot if you select "Forum Featured" when placing or editing your ad!

All Forums >> Glow Engines, Gas Engines, Fuel & Mfg Support Forums >> Engine Manufacturers Direct Support Forum >> Jett Engineering Support >> Jett 50 possible lean run problems.
Page: [1]

Login
Message << Older Topic   Newer Topic >>
Jett 50 possible lean run problems. - 4/13/2003 8:38:59 AM   
mtthomps



Posts: 307
Joined: 10/4/2002
From: League City, TX, USA
Status: offline 		I have a fairly new Jett .50 that I think has a problem. I was testing the engine in the plane for the first time and on vertical the RPM noticably lagged for about 10 seconds and then the engine quit. I had the needle set for pretty rich on the ground, about 800 rpm below peak. When I landed the dead stick, I noticed that the engine was VERY hot. I let it cool, and from this point forward, the engine is VERY hard to turn over. I think I had a lean run, in other words. I have run the engine many times since, but the problem has never gotten any better. It does not seem to affect the performance that I can tell. I have not tached it. Do I need a new piston and sleeve?
       Post #: 1

Jett 50 possible lean run problems. - 4/14/2003 9:55:29 PM   
bob27s



Posts: 4821
Joined: 4/9/2002
From: Cleveland, OH, USA
Status: offline 		Hi.....

Thanks for writing.

First, as for hard to turn-over....
Jett engines normally have a very tight seal at top-dead-center. They may even make an audible 'squeek' when you turn them, and you will feel this fit even with the glowplug removed. An engine like this has an excellent fit, and will provide top performance as you continue to run it. If what you are feeling is different from a compression fit (tough to turn anywhere during the stroke) something may have been damaged internally.

Second, to protect your investment.... if the engine ever goes lean and sags in flight....... level out, throttle back, and shut down the engine as soon as you can. A sustained lean run is the only real way you can damage Jett engine in operation.

800 rpm down is ok. I usually only set down 500 rpm for sport use (10x6 or 9x8 prop), or 800-900 down for speed (diamond dust type) applications where I am using a smaller prop that unloads a lot in the air. The muffler pressure from a Jett muffler is generally higher than that provided by most stock mufflers, so you should have pleanty of fuel pressure for any application.

If the engine is going lean in vertical, you may have a fuel system problem.

Let me assume for a moment that the tank placement is in the 'conventional' location behind the firewall, and not far off (up and down) from center line from the carb inlet.

First, check the obvious. Make sure there are no holes, kinks or restrictions in either the fuel supply or muffler pressure lines. During ground operation, watch the fuel supply line to ensure there are no visable air bubbles. Check this situation at both the 800 rpm down, and near peak rpm.

Make sure the clunk in the tank can move freely, and the clunk line does not have any holes in it (happens more than you might think). A hole in the clunk tube where it attaches to the brass tube will cause the symtoms you described... the tank will supply fuel in level flight (down to the level the hole is) and when the tank is full (ground run-up). But when you pull vertical, it will suck through the hole air along with the fuel from the clunk end. That will cause the engine to immediately go lean in a climb.

If none of the above is the answer....

95% of the trouble calls we get are fuel system issues. About 75% of those are fuel tank installation issues.

If the tank is not properly installed and isolated from the aircraft structure, the fuel can turn to foam in flight, resulting in a lean engine run (and possibly toasting the engine). Jett engine unload quite a bit in the air, so in many cases, you will not see any air bubbles or foam in the fuel while it is running on the ground. But trust me, the condition will manifest itself while in the air. In some cases customers stated that they did not have the problem with 'another' engine. The case there is, the Jett is turning (for example) 1000 rpm more, and creating an airframe vibration frequency that simply had not existed before.

Make sure the fuel tank is wrapped in foam, and is not directly touching any aircraft structure. This will help isolate it from the airframe vibration that is causing the foam.

Check the items listed above, and feel free to email me or post here with any additional information you can share. Knowing the aircraft and prop sometimes can help.

I hope this has been helpful.

Bob Brassell

[email]bob27s@hotmail.com[/email]

(in reply to mtthomps)
       Post #: 2

Jett 50 possible lean run problems. - 4/14/2003 10:23:11 PM   
mtthomps



Posts: 307
Joined: 10/4/2002
From: League City, TX, USA
Status: offline 		Thanks for your reply, yes the tightness is at TDC, not anywhere else in the stroke, and not if I flip the engine over quickly. It does make the audible squeak that you mentioned. Muffler pressure is the one place I was worried about, I thought that there might not be sufficient pressure into the tank. There might indeed be an air leak when the plane is vertical, I will check for this to see if there are any bubbles coming from the tank when I hold the plane vertical and go to full throttle on the ground.

(in reply to mtthomps)
       Post #: 3

Jett 50 possible lean run problems. - 4/15/2003 2:05:39 AM   
bob27s



Posts: 4821
Joined: 4/9/2002
From: Cleveland, OH, USA
Status: offline 		Sounds good...

Let me know how you make out.

Bob

(in reply to mtthomps)
       Post #: 4

Page:   [1]
All Forums >> Glow Engines, Gas Engines, Fuel & Mfg Support Forums >> Engine Manufacturers Direct Support Forum >> Jett Engineering Support >> Jett 50 possible lean run problems.
Page: [1]





Jump to:


Google 



Search | Marketplace | Event Calendar | Local Clubs | Magazine | Product Ratings | New Products | Discussion Forums

Photo Gallery | Member Video Posts | RCU Video Gallery | Instructor Search | Field|Track|Marina Search

Advertisers | Hobby Vendor Resources | Rate Manufacturers | Sign In/Sign Up

SITE MAP!   : :   FORUM RULES

© 2001 - 2007 24-7 RC, LLC, all rights reserved.

Charities we support that also need your help
Yorkie Rescue | Humane Society | ASPCA | Crohn's-Colitis America

Kaango.com Classifieds

0.641RCU1