Exasperating YS .91 FZ
10-28-2005, 10:55 AM
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Exasperating YS .91 FZ
I seldom get stumped by an engine, but this one has me baffled. It quits after a few seconds at 4,500 rpm, yesterday PM I put a new diaphragm, plunger, spring and plunger tip in it. It still quits at 4,500 rpm. I verified that my own .91 FZ runs perfectly and put my regulator, lock, stock and barrel on the troublesome one, no joy. The man who owns it brought some green 20% fuel with it. I tried my WildCat 20/20 which has 95/5 syn. castor blend, it has more compression when using the WildCat but no improvement in the way it runs. He put a new OS-f in it and I put another new OS-f in it, no change. Whatever is wrong with it makes the regulator ineffective. Anyone want to take a shot?
10-28-2005, 12:34 PM
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RE: Exasperating YS .91 FZ
Hobbsy,
I know it will have been early on your check list, but from experience I have found that even the smallest inlet valve leak can upset carburetion.
Worth a look...?
I know it will have been early on your check list, but from experience I have found that even the smallest inlet valve leak can upset carburetion.
Worth a look...?
10-28-2005, 12:37 PM
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RE: Exasperating YS .91 FZ
Do you have pressure in your tank? If not, what about the check valve?
The gasket under the air box is bad about sucking in on the bottom side. You might need a mirror to see under there if the engine is mounted.
Did your FZ still run after putting the parts back into it.
Is the valve cover sealed good?
Do you have it plumbed up right? A good proof would be to see how your FZ runs with the same set-up?
The gasket under the air box is bad about sucking in on the bottom side. You might need a mirror to see under there if the engine is mounted.
Did your FZ still run after putting the parts back into it.
Is the valve cover sealed good?
Do you have it plumbed up right? A good proof would be to see how your FZ runs with the same set-up?
10-28-2005, 01:38 PM
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RE: Exasperating YS .91 FZ
Thanks guys, it swells the tank up and after one half hour of just sitting it still had pressure in the tank, I ran mine on exactly the same tank and hoses. My friend says it never ran well enough to fly since he bought it. It absolutely howls at full song. I'm going to suggest he send it back for Richard to look at. If I work on it any more I'll use my ball bat on it.
11-02-2005, 02:48 PM
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RE: Exasperating YS .91 FZ
Does it quit at a steady 4500 throttle setting or only while passing through 4500? Is it smoking a lot or not at all? Midrange problems are almost always regulator problems. Is the regulator screw flush with the bottom of the housing? If you screw in the regulator does the midrange get richer?
ORIGINAL: hobbsy
I seldom get stumped by an engine, but this one has me baffled. It quits after a few seconds at 4,500 rpm, yesterday PM I put a new diaphragm, plunger, spring and plunger tip in it. It still quits at 4,500 rpm. I verified that my own .91 FZ runs perfectly and put my regulator, lock, stock and barrel on the troublesome one, no joy. The man who owns it brought some green 20% fuel with it. I tried my WildCat 20/20 which has 95/5 syn. castor blend, it has more compression when using the WildCat but no improvement in the way it runs. He put a new OS-f in it and I put another new OS-f in it, no change. Whatever is wrong with it makes the regulator ineffective. Anyone want to take a shot?
I seldom get stumped by an engine, but this one has me baffled. It quits after a few seconds at 4,500 rpm, yesterday PM I put a new diaphragm, plunger, spring and plunger tip in it. It still quits at 4,500 rpm. I verified that my own .91 FZ runs perfectly and put my regulator, lock, stock and barrel on the troublesome one, no joy. The man who owns it brought some green 20% fuel with it. I tried my WildCat 20/20 which has 95/5 syn. castor blend, it has more compression when using the WildCat but no improvement in the way it runs. He put a new OS-f in it and I put another new OS-f in it, no change. Whatever is wrong with it makes the regulator ineffective. Anyone want to take a shot?
11-02-2005, 03:43 PM
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RE: Exasperating YS .91 FZ
If you have better compression when changing fuel (i.e., changing oil), it may be a compression/valve seal issue, but you mentioned it didn't run any better, so probably not the problem.
Everyone else covered the basic leaks, fuel pressure, etc., so I'll throw this in.
Check your prop/spinner. If you are using a spinner, ditch it and try prop only. Check the spinner back plate for slippage. I've seen some YS's not run right due to small slipping here. Everything looks normal, prop nut is tight, but thrust washer not grabbing spinner/prop properly as the engine starts to make good power. The result is the engine runs like poo and often abruptly dies and a lot of head scratching goes on as the needles seem to have no effect. I typically only encouter this when a pilot used a plastic spinner, but I've seen a few metal backplates also suffer this issue.
I tend to agree that midrange issue are generally regulator related. It may be that the regulator valve seat is all gummed up or not seating properly. If I remember correcly, to get to the seat, you must tear down the regulator from the outside (remove the brass adjustment screw.), so I'd just try back flushing first. You can also try pressuring the system by running the engine and then letting it sit a spell. If fuel starts leaking out the engine, the reg seat is not seating properly.
Cheers
Everyone else covered the basic leaks, fuel pressure, etc., so I'll throw this in.
Check your prop/spinner. If you are using a spinner, ditch it and try prop only. Check the spinner back plate for slippage. I've seen some YS's not run right due to small slipping here. Everything looks normal, prop nut is tight, but thrust washer not grabbing spinner/prop properly as the engine starts to make good power. The result is the engine runs like poo and often abruptly dies and a lot of head scratching goes on as the needles seem to have no effect. I typically only encouter this when a pilot used a plastic spinner, but I've seen a few metal backplates also suffer this issue.
I tend to agree that midrange issue are generally regulator related. It may be that the regulator valve seat is all gummed up or not seating properly. If I remember correcly, to get to the seat, you must tear down the regulator from the outside (remove the brass adjustment screw.), so I'd just try back flushing first. You can also try pressuring the system by running the engine and then letting it sit a spell. If fuel starts leaking out the engine, the reg seat is not seating properly.
Cheers
11-02-2005, 06:03 PM
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RE: Exasperating YS .91 FZ
John,
Wow! Thanks for bringing that up. It has been a long time since I saw it but you are absolutely correct! I had exactly the same problem with a CB Associates spinner and Zinger (EEEWWW) prop. The prop was slipping on the backplate and dragging the front of the spinner around with it.
Wow! Thanks for bringing that up. It has been a long time since I saw it but you are absolutely correct! I had exactly the same problem with a CB Associates spinner and Zinger (EEEWWW) prop. The prop was slipping on the backplate and dragging the front of the spinner around with it.
ORIGINAL: JohnW
If you have better compression when changing fuel (i.e., changing oil), it may be a compression/valve seal issue, but you mentioned it didn't run any better, so probably not the problem.
Everyone else covered the basic leaks, fuel pressure, etc., so I'll throw this in.
Check your prop/spinner. If you are using a spinner, ditch it and try prop only. Check the spinner back plate for slippage. I've seen some YS's not run right due to small slipping here. Everything looks normal, prop nut is tight, but thrust washer not grabbing spinner/prop properly as the engine starts to make good power. The result is the engine runs like poo and often abruptly dies and a lot of head scratching goes on as the needles seem to have no effect. I typically only encouter this when a pilot used a plastic spinner, but I've seen a few metal backplates also suffer this issue.
I tend to agree that midrange issue are generally regulator related. It may be that the regulator valve seat is all gummed up or not seating properly. If I remember correcly, to get to the seat, you must tear down the regulator from the outside (remove the brass adjustment screw.), so I'd just try back flushing first. You can also try pressuring the system by running the engine and then letting it sit a spell. If fuel starts leaking out the engine, the reg seat is not seating properly.
Cheers
If you have better compression when changing fuel (i.e., changing oil), it may be a compression/valve seal issue, but you mentioned it didn't run any better, so probably not the problem.
Everyone else covered the basic leaks, fuel pressure, etc., so I'll throw this in.
Check your prop/spinner. If you are using a spinner, ditch it and try prop only. Check the spinner back plate for slippage. I've seen some YS's not run right due to small slipping here. Everything looks normal, prop nut is tight, but thrust washer not grabbing spinner/prop properly as the engine starts to make good power. The result is the engine runs like poo and often abruptly dies and a lot of head scratching goes on as the needles seem to have no effect. I typically only encouter this when a pilot used a plastic spinner, but I've seen a few metal backplates also suffer this issue.
I tend to agree that midrange issue are generally regulator related. It may be that the regulator valve seat is all gummed up or not seating properly. If I remember correcly, to get to the seat, you must tear down the regulator from the outside (remove the brass adjustment screw.), so I'd just try back flushing first. You can also try pressuring the system by running the engine and then letting it sit a spell. If fuel starts leaking out the engine, the reg seat is not seating properly.
Cheers
