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All Forums >> Glow Engines, Gas Engines, Fuel & Mfg Support Forums >> Engine Manufacturers Direct Support Forum >> YS Engines Support >> YS 120 fuel pressure
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YS 120 fuel pressure - 6/14/2008 8:57:08 AM   
OldFart1


 

Posts: 210
Joined: 12/21/2005
From: Lakewood , CA, USA
Status: offline 		...as in I don't have any

Used YS 120, one of the earlier generations (no slow speed screw), installed inverted. Tank connections are fine, motor is producing NO fuel pressure. Pulled the check valve to see if maybe it was bad - motor will (barely) idle, but does as the throttle is advanced. Pulled the connection at the fuel pump - nothing. Tank is NOT pressurizing.

If I invert the plane on the stand (puts the tank above the carb) it runs (gravity flow of fuel.

What do I check for?

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Jeff
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RE: YS 120 fuel pressure - 6/14/2008 2:11:09 PM   
MOTORMAN37



Posts: 2059
Joined: 10/26/2002
From: CLINTONVILLE, WI, USA
Status: offline 		oldfart,
The idle circut is airbleed anyways, it transfers to pressure just above idle. It sounds like you have a bad airleak, or a worn out ring.

(in reply to OldFart1)
       Post #: 2

RE: YS 120 fuel pressure - 6/14/2008 2:23:50 PM   
dmccormick001


 

Posts: 93
Joined: 2/13/2005
From: Soddy Daisy, TN, USA
Status: offline 		1. Bad connections to regulator, fuel tees, fuel dots, tank connections..... basically everything. Obviously you could be losing it anywhere.
2. Bad or improperly installed check valve. Make sure it isn't installed backwards. Flow should be towards tank away from engine.
3. Cracked/punctured/leaking diaphragm in regulator. Would cause pressure to be lost before reaching tank.
4. Cracked tank. (unlikely) You should be able to see fuel seeping around a crack if there were one.

Bottom line is this....your engine is almost certainly producing pressure. The pressure is actually produced by the up and down motion of the piston inside the cylinder. As is moves "down" (away from the head/glow plug) is produces a vacuum above it, which draws fuel into the cylinder. But is also produces a corresponding pressure inside the crankcase as the air under it is displaced, and this is the pressure that is sent to the tank. It doesn't depend on the action of any diaphragm or valve, but is caused by the action of the motor, and it is channeled out a small port drilled into the engine under the regulator valve diaphragm. So, unless your motor is just completely worn out, which doesn't seem likely since you said it runs OK with the tank above the carb, then it's producing pressure. You're just losing it somewhere along the way.

The regulator isn't actually a pump, just a regulator for the flow of fuel going to the carb. The fuel is "pumped" to the engine by pressurizing the tank with the positive crankcase pressure entering the tank from the vent tube.

I just had an idea. You could place a longer length of fuel tubing on the output side of the regulator, either before or after the check valve, put the end of it into a tank or bottle with some fuel already in it, and then turn the motor over with your starter motor. See if you get any bubbles in the bottle. If you do, that's your pressure. Now just find out where it's gettin' away from you.

Hope this helps.

David

(in reply to OldFart1)
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RE: YS 120 fuel pressure - 6/14/2008 3:59:34 PM   
petec



Posts: 550
Joined: 1/26/2002
From: Beaver Falls, PA, USA
Status: online 		It could also be gelled fuel in the regulator passages on the pressure side.

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RE: YS 120 fuel pressure - 6/14/2008 7:47:07 PM   
OldFart1


 

Posts: 210
Joined: 12/21/2005
From: Lakewood , CA, USA
Status: offline 		We tried last night to eliminte all the variables in the "circuit", here's what we tried. For talking purposes, the supply line FROM the tank is pink, the short line from pump to carb is pink, the return from pump TO tank is blue.

Eliminated the fuel dots from the equation (put in a straight connector instead of a tee) - no difference

Eliminated the check valve in the blue line (and I'm going to get another anyway, there's no spring in this one - with just a ball bearing it seems to "check" against pressure BOTH ways) - no pressure

Pulled the blue line at the pump and flipped the motor over - no fuel coming from pump

Pulled the pink line from pump to carb and flipped the motor over - no fuel pressure

Tank isn't leaking, checked that

David - can you expand on item 3? (and I'll try your bubbles in the bottle idea)

Petec - how would I check your idea (and cure it)

Motorman37 - which ring are you talking about?

Damn thing runs if it's inverted, maybe I just need to launch it that way

Fuel lines are set up per this: http://www.geistware.com/rcmodeling/glowpower/ys120.htm


Thanks to all of you!

< Message edited by OldFart1 -- 6/14/2008 7:54:13 PM >

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Jeff

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RE: YS 120 fuel pressure - 6/15/2008 2:05:29 AM   
petec



Posts: 550
Joined: 1/26/2002
From: Beaver Falls, PA, USA
Status: online 		Jeff,

I'll take some pictures and post them for you as soon as I can steal the camera from my wife. Basically you need to pull the regulator ousing off teh engine and make sure none of the tiny passages are clogged. You will need to do this in a clean environment as dirt is the enemy of the regulator and also you will need a new gasket for the housing. If you are not comfortable doing this you might consider sending it to YS Parts and Service.

First things first though, get a good check valve on that engine. The check valve allows pressure to only go one way and that is toward the tank. If yours does not have a spring in it that is an issue you need to address.

Pete

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RE: YS 120 fuel pressure - 6/15/2008 4:49:23 AM   
mjfrederick


 

Posts: 563
Joined: 8/18/2006
From: Baton Rouge, LA, USA
Status: offline 		The ball bearing-type check valves really do not work in YS applications. You need to get the YS one. Also, for testing purposes, you cannot remove the check valve. The ONLY way pressure builds in the tank is a result of the check valve stopping flow back into the engine.

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RE: YS 120 fuel pressure - 6/15/2008 8:02:30 AM   
OldFart1


 

Posts: 210
Joined: 12/21/2005
From: Lakewood , CA, USA
Status: offline 		MJ - who carries the YS check valves?

Fiddled some more this afternoon - then boxed it up, sending it to Minden on Monday.

< Message edited by OldFart1 -- 6/15/2008 8:03:10 AM >

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RE: YS 120 fuel pressure - 6/15/2008 12:36:00 PM   
petec



Posts: 550
Joined: 1/26/2002
From: Beaver Falls, PA, USA
Status: online 		Central Hobbies usually has the check valves in stock.

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RE: YS 120 fuel pressure - 6/15/2008 3:40:53 PM   
mjfrederick


 

Posts: 563
Joined: 8/18/2006
From: Baton Rouge, LA, USA
Status: offline 		Yes, Central usually has them, but they were out a couple weeks ago when I placed an order. If they're out of stock, you may be able to get one from YS Parts and Service.

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RE: YS 120 fuel pressure - 6/15/2008 7:17:47 PM   
OldFart1


 

Posts: 210
Joined: 12/21/2005
From: Lakewood , CA, USA
Status: offline 		The check valve I have is from Central - the only one they listed (and has the ball bearing - but no spring)

I'll try YS parts and service

thanks!

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Jeff

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RE: YS 120 fuel pressure - 6/15/2008 10:13:58 PM   
Troy Newman


 

Posts: 2429
Joined: 12/30/2001
From: Goodyear, AZ, USA
Status: offline 		You need to have a YS check Valve NOT a Tettra version

YS part#0405

This is what you need. The YS version only has a small silicone flapper...There is no spring....

The ball Bearing Spring types will not work properly on the YS engines. Also the check valve part is not optional. You can't remove it and have the engine run properly. In fact the engine could be damaged if you run the engine without the proper check valve in place.


Troy Newman

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RE: YS 120 fuel pressure - 6/15/2008 11:30:09 PM   
OldFart1


 

Posts: 210
Joined: 12/21/2005
From: Lakewood , CA, USA
Status: offline 		Thanks Troy, I'll order a couple. Would the repair depot in Minden have them, if so I'll buy a couple and have them come back with the motor.

Oh, and Troy - great to see you online!

< Message edited by OldFart1 -- 6/15/2008 11:31:25 PM >

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Jeff

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RE: YS 120 fuel pressure - 6/18/2008 2:27:06 PM   
Cyberwolf



Posts: 1042
Joined: 1/10/2004
From: Blackfoot , ID, USA
Status: offline 		Why in the world would Central sell a check valve for the YS line of engines that won't work properly? I have a couple of these ball and spring valves and have had my share of running issues and low tank pressure and blamed everything but the check valve. Thanks for the heads up .

Old Fart I have seen a Oring on a pushrod tube cause a leak large enough to cause a no or low tank pressure issue. So what I am saying is it doesnt take much of a of leak to create low or no tank pressure. I make it a habit now to replace all of the Orings and gaskets if I take the engine down for any reason other than adjusting the valves.
But again the gasket on the valve cover can be a source for leakage also.
A YS 120 engine has to be air tight to be able to run correct tank pressure with a good check valve, tank and lines.
One more thought the rubber plug in the back the carb body holds in to the cyl can be another source of leakage.
Good luck.

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RE: YS 120 fuel pressure -