91 FZ won't idle  
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All Forums >> Glow Engines, Gas Engines, Fuel & Mfg Support Forums >> Engine Manufacturers Direct Support Forum >> YS Engines Support >> 91 FZ won't idle
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91 FZ won't idle - 7/2/2008 5:19:34 AM   
42etus



Posts: 128
Joined: 7/8/2005
From: La Pine, OR, USA
Status: offline 		I've got a 91FZ that until now has run and idled great. Now it still runs great at top end and mid range. When I drop it to a idle, it will idle fine for 10 seconds or so then suddenly stop. It doesn't load up then stop nor does it pick up before it stops. It just stops suddenly after 10 seconds of good idle. I have adjusted the idle screw from 1/2 turns open to 3 turns open and while that changes the quality of the idle, it doesn't change the problem. The engine still won't idle for more than 10 seconds or so. I have always used Cool Power 30% heli fuel, and the tank holds pressure well. The regulator screw is set about 1/4 turn in (lean) from flush to give me a reliable mid-range.
I've done the following to no avail:
Checked the valve adjustment. It's within specs
Replaced the diaphram, plunger and spring in the regulator.
Tried 3 different new OS "F" glow plugs
Inspected the fuel system from clunk to the engine
Checked the fuel filter, was clean
Dismanteled the carb, washed all the parts in alcohol and reassembled it
Inspected the engine for leaking gaskets or bad O-rings
I'm baffeled. Anyone seen this or have any ideas?
Paul


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RE: 91 FZ won't idle - 7/2/2008 12:03:31 PM   
dmccormick001


 

Posts: 123
Joined: 2/13/2005
From: Soddy Daisy, TN, USA
Status: offline 		Try leaving your glow ignitor connected and see if that makes any difference. If it continues to idle OK with the ignitor connected, then the idle is probably rich, so lean it up a shade. You may need to lean the regulator, not just the idle screw. If the regulator is set too rich, it will allow too much fuel to pass at idle and flood the engine just the same. It controls fuel flow at all speeds, not just mid or high range.

David

(in reply to 42etus)
       Post #: 2

RE: 91 FZ won't idle - 7/2/2008 10:28:18 PM   
42etus



Posts: 128
Joined: 7/8/2005
From: La Pine, OR, USA
Status: offline
quote:

ORIGINAL: dmccormick001

Try leaving your glow ignitor connected and see if that makes any difference. If it continues to idle OK with the ignitor connected, then the idle is probably rich, so lean it up a shade. You may need to lean the regulator, not just the idle screw. If the regulator is set too rich, it will allow too much fuel to pass at idle and flood the engine just the same. It controls fuel flow at all speeds, not just mid or high range.

David

Well it's gone from bad to worse. I tried leaving the glow igniter on as you suggested and it seemed to idle longer before it quit. But the mid-range has gotten very rich. I had to screw the regulator screw in all the way! to get the mid-range to stop loading up. Strange. Even with the regulator screw in all the way, the top end is just fine with lots of power and no signs of being too lean. The mid-range is now fine, but the thing still won't idle longer than 10 seconds or maybe 20 with the igniter on. Seems like it's still too rich. I've opened (CCW) the idle screw out 3 full turns from closed and it still dies. I'm thinking that something must be wrong in the regulator for it to be acting this way, even though I have replaced the diaphram, plunger (both pieces) and the spring. The engine should be seriously lean at full throttle with the regulator screw in that far, but it isn't. Any ideas?
Paul

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RE: 91 FZ won't idle - 7/3/2008 12:56:53 AM   
mjfrederick


 

Posts: 593
Joined: 8/18/2006
From: Baton Rouge, LA, USA
Status: offline 		OK, I brainstormed this one for a while, and this is what I've come up with. Too rich means one of two things: not enough air or too much fuel. You seem to have covered the too much fuel with the regulator, so lets look at the not enough air. There could be a problem (clog, etc.) somewhere in the idle air bleed area. Check all the jetting in the carb for any debris, maybe tear it all down and give it a good flushing with some fuel and blow it all out good with compressed air. I still think the regulator could use a double-check to make sure the assembly is OK. Lastly, for some reason I'm also thinking intake valve. Not sure if it could cause this problem, but check to make sure that it's not adjusted too tight (holding the valve open) or sticking. Hope something here helps... this is a bear of a problem you're dealing with.

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Maybe the Dingo ate your baby

(in reply to 42etus)
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RE: 91 FZ won't idle - 7/3/2008 1:39:49 AM   
petec



Posts: 659
Joined: 1/26/2002
From: Beaver Falls, PA, USA
Status: offline 		I have to agree that it might not be a bad idea to remove the butterfly from the throttle body just to make sure there isn't anything on the airbleed side. I had a 1.20 FZ that would cut otu on down lines and after much troubleshooting found a piece of grass was partially blocking the airbleed.

If a valve was being partially hed open you would be down on compression and also be able to hear the hiss of compression blowing back out the intake when pulling it through by hand.

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RE: 91 FZ won't idle - 7/3/2008 2:00:44 AM   
nonstoprc



Posts: 1045
Joined: 9/9/2003
From: austin, TX, USA
Status: offline 		Some other items to check.

1. different fuel
2. leaks in places that have not been checked.

I suspect #2, if the engine has been running good for a while. For example, is air chamber gasket nice and solid?

(in reply to petec)
       Post #: 6

RE: 91 FZ won't idle - 7/3/2008 4:07:28 AM   
42etus



Posts: 128
Joined: 7/8/2005
From: La Pine, OR, USA
Status: offline 		Well, as I said first off, I have dis-assembled and cleaned the carb. I've also double checked the valve clearences. The fuel is a fresh jug, that the engine ran fine on a week ago. I've had the regulator apart 3 times now, and it looks fine inside. I thought that I understood this engine, until now, but I'm really stumped this time. I guess I'm just grasping at straws before I pack the thing up and send it to YS Parts & Service.
Paul

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RE: 91 FZ won't idle - 7/3/2008 4:27:49 AM   
nonstoprc



Posts: 1045
Joined: 9/9/2003
From: austin, TX, USA
Status: offline 		The same problem happened to my 110 when it was new. It will quit during idle for no reason. YS services replaced the cylinder head gasket.

Leaking is always hard to figure out why. One can replace all gaskets in anticipation of a cure, but there is no guarantee. Sending it back probably is a better idea. Regards.

(in reply to 42etus)
       Post #: 8

RE: 91 FZ won't idle - 7/3/2008 6:34:46 AM   
mjfrederick


 

Posts: 593
Joined: 8/18/2006
From: Baton Rouge, LA, USA
Status: offline 		I was thinking about throwing in the head gasket when I mentioned the intake valve... Come to think of it, check the exhaust valve too... and possibly the piston ring. I don't think it's a leak in the normal use of the term (fuel, intake air) since the only "leak" that can cause a rich condition is the regulator getting stuck open... all others tend to cause lean conditions because they reduce fuel flow or allow more air in than should be getting in. My gut is still telling me something in the idle bleed or in the head causing this problem. The more I think about it, the more I come up with to check. Now that I think about it, I believe a compression loss, no matter how miniscule, will retard the timing and cause the engine to seem to be running rich. I say this just based on the fact that a lean engine will suffer from detonation (premature ingition), so a rich engine should suffer from the ignition happening later. Reduced compression should cause the same problem since our fuels require a specific amount of compression before the glow plug can ignite them. If you end up having to send this one to Richard, make sure to let us know what the fix is...

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Maybe the Dingo ate your baby

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RE: 91 FZ won't idle - 7/4/2008 12:35:20 AM   
42etus



Posts: 128
Joined: 7/8/2005
From: La Pine, OR, USA
Status: offline 		I'm a little puzzled when you guys talk about the head or head gasket as the head and cylinder are one piece. There is no head gasket as I normaly think of it. Any way, I pulled the cylinder off just to have a look. Things seemed fine. The ring wasn't stuck or gummed up at all. Infact it looked great. I don't here any compression leaking in either the intake or the muffler at TDC so I think the valves are sealing good. I'm leaning toward something in the regulator being amiss. Like I said, the high end is great with the regulator screwed in all the way. I would think it shouldn't even run like that. Too much going on in the next few days to mess with it ( 4th of July and all), maybe Monday I can work on it some more. Stay tuned.
Paul

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RE: 91 FZ won't idle - 7/4/2008 1:25:26 AM   
petec



Posts: 659
Joined: 1/26/2002
From: Beaver Falls, PA, USA
Status: offline 		I have to agree that with the regulator screwed the whole way in it should not do anything but maybe idle. Do you have a spare spring to try in the regulator? If not you might try to stretch the spring out a bit. COnsidering the age of the engine the regulator spring might have taken a set.

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Team Black Magic
Pattern Junkie..Revver Brother #82..Gear Head

(in reply to 42etus)
       Post #: 11

RE: 91 FZ won't idle - 8/2/2008 9:51:22 PM   
42etus



Posts: 128
Joined: 7/8/2005
From: La Pine, OR, USA
Status: offline 		Update........
A couple weeks ago I packed the engine up and sent it to Richard at YS Parts & Service along with a note explaining things. I got it back yesterday and took it to the field today for a test flight. After a little bit of needle twisting (very little) it is running great, nice top end and a great idle. I'm happy again. This engine is a real powerhouse. OK, so what did Richard do to it you ask? He replaced all the gaskets and put in a new diaphram in the regulator. A stupid simple fix. Exactly what the problem was is anyones guess, I'm leaning toward a bad gasket causing an air leak, but who knows. Maybe there were two seperate problems, leaky gaskets and a bad diaphram. All I know is that it runs great now. Thanks Richard!
Paul

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I know right from wrong.....Wrong is the fun one

(in reply to 42etus)
       Post #: 12

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