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HelicopterMain Discussion › YS 80st problem- diaphragm out of adjustment?
04-20-2018 03:35 PM  30 days agoPost 1
motorrc

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canton ohio usa

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I have a YS 80st that I can get to idle but when I try to ramp up the motor seems to over rev and then quit, like it is too lean. I have tried every carburetor setting there is with no improvement. I have rebuilt the carburetor, tried fuel that I know is good, new glow plug, changed out the entire fuel line including the fuel filter, water tested the tank for leaks, checked the one way value and it is fine. Could the diaphragm be out of adjustment and if so, how do I adjust it?

if it doesn't fit, make it fit.

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04-20-2018 05:16 PM  30 days agoPost 2
TMoore

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Cookeville, TN

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When you try to start it and build a little pressure in the tank what happens if you pull the fuel line off the nipple?

I've rebuilt a ton of those engines and they typically would go back together easily. It might be to your benefit to pull the carb and regulator assy and take another look.

Go back to basics and check your steps.

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04-20-2018 05:19 PM  30 days agoPost 3
wjvail

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Meridian, Mississippi

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motorrc
I have rebuilt the carburetor...
Did you install new carb parts or just clean, inspect and reinstall the original parts? Did you start with a rebuild kit?

Have you given the check valve a good going over? Does the tank pressurize and hold pressure for a period of time?

Head and back-plate bolts are tight?

It's hard to tell what might be wrong and I'm just throwing out some ideas.

Bill

"Well, Nothing bad can happen now."

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04-20-2018 05:52 PM  30 days agoPost 4
JLF92677

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Southern California

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Since you have rebuilt the carb, did you change the screw adjustment on the bottom black plate of the diaphragm regulator housing assembly part # S8138A (see manual.) Subject diaphragm adjustment screw is factory set and covered with a white silicone dot to prevent user adjustment. If you changed the adjustment on this screw that is most likely your problem.

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04-20-2018 10:41 PM  30 days agoPost 5
motorrc

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canton ohio usa

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Thanks for the help folks. To answer some questions, no I did not change the factory set screw on the diaphragm. I suspect that might be the problem but I have no idea how to reset it or even check it. When I rebuilt the carburetor I replaced all O rings and gaskets, soaked the disassembled carburetor parts in fuel for 24 hours, the blew out all the orifices with compressed air and reassembled. When I disconnect the pressure line coming from the back of the motor to the fuel tank, a hissing sound is heard.

if it doesn't fit, make it fit.

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04-20-2018 10:43 PM  30 days agoPost 6
motorrc

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canton ohio usa

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ps I have not pulled the fuel line off the carburetor nipple.

if it doesn't fit, make it fit.

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04-20-2018 10:45 PM  30 days agoPost 7
motorrc

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canton ohio usa

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pps the check valve seems to be working well as pressure does build up and is maintained. Back bolts on the motor were checked and are tight.

if it doesn't fit, make it fit.

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04-21-2018 12:53 AM  30 days agoPost 8
JuanRodriguez

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The Villages, Florida

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So when you "rebuilt" the carburetor, did you not replace the old diaphragm with a new one ?? That is the heart of the system......and you can't just visually inspect it to say it's OK.....
ps I have not pulled the fuel line off the carburetor nipple.
And that is the place any accumulated junk is going too collect.... I would pull that line (better yet, replace it) and carefully inspect that opening for junk that may be restricting the fuel flow.....

Been there, done that and old enough to know better.....

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04-21-2018 02:10 AM  30 days agoPost 9
wjvail

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Meridian, Mississippi

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Can I put in a plug for fuel filters.?.? I used to not recommend them because they would plug up and stop fuel flow faster than the carburetor they were supposed to be protecting.

New generation filters will eat a ton of trash and still flow more than enough fuel to keep you running. They are easy to inspect and clean. And if you need one more reason to install one, they are well made and cheap (alright, that's two more reasons).

I recommend Horizon Hobby "Dynamite" brand but there are many with a similar filter element. I know - Dynamite isn't generally thought of as a premium brand but these just work. You're looking for a filter with an element similar to the one pictured below.

https://www.horizonhobby.com/pro-fuel-filter-dyn2006

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04-21-2018 01:14 PM  29 days agoPost 10
DS 8717

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https://shop.textalk.se/shop/21984/files/YS/80ST-E.pdf
sounds too lean in mid range...

YOU ONLY LIVE ONCE..IF YOU LIVE IT RIGHT THATS ALL YOU NEED

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04-21-2018 01:54 PM  29 days agoPost 11
motorrc

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canton ohio usa

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I did not replace the diaphragm, just inspected it and it looked ok. I should clarify, I did inspect and replace the fuel line at the carburetor nipple, however, when I pressure tested the system, I disconnected at the tank not the carburetor nipple, that is what I meant in my earlier post. I have replaced the fuel filter with the one suggested.

if it doesn't fit, make it fit.

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04-21-2018 02:23 PM  29 days agoPost 12
Four Stroker

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Atlanta

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To find out if the regulator is working take out the glow plug and the high speed needle and spin the engine with the starter at high throttle - full tank attached. If all is well fuel will squirt out of the needle hole. With tank pressure, turn the engine over manually slowly. Squirt should start AND stop. Should also work with the hover needle. If no fuel squirts out, something is clogged up.

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04-21-2018 02:39 PM  29 days agoPost 13
Four Stroker

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Atlanta

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There are valuable tools for YS pressure systems:

YS nipple JB welded into 1/8 NPT 0~15 PSI pressure gauge and a pressure pump made from junk.

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04-22-2018 01:44 AM  29 days agoPost 14
Dirtpen

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Illinois

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I had one do that long ago, it was sucking air from an old fuel line cracked inside the fuel tank. Everything good but no go. Couldn't see the fuel line through plastic tank. And it was. Sounds like it's suck in air from somehow. I just thought the diagram goes in one way. Upside down ,I don't know but it's suckin air from somehow.or blocked off .

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04-22-2018 03:23 AM  29 days agoPost 15
thtoyman

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Gone ,Flying.

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I had one do the same thing. couldn't get it right. and now its in junk box in my shop for parts

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04-22-2018 08:53 AM  29 days agoPost 16
motorrc

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canton ohio usa

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Thanks dirtpen, I have replaced the line inside the tank.

Four stroker, thanks for the info on testing, I'll give it a try. Could you provide more information on how to use your pressure tester, such as, where to connect it, what the pressure should read etc?

if it doesn't fit, make it fit.

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04-22-2018 07:35 PM  28 days agoPost 17
JuanRodriguez

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The Villages, Florida

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As I've already stated, replace the diaphragm..... it's the heart of the system....

Been there, done that and old enough to know better.....

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04-22-2018 09:14 PM  28 days agoPost 18
Four Stroker

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Atlanta

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What Juan said. If you make sure that none of the passages or orifices are clogged and replace all of the gaskets, O-rings, and the diaphragm, then the engine will run fine. This isn't rocket science.

In order for this regulator to work, the silicone rubber diaphragm must be in original as designed condition. Any non-silicone safe after run oil will swell, warp, or distort the regulator diaphragm even if it doesn't dissolve it into a puddle. Many muy macho sponsored factory pilots that are worshiped by the masses will disagree and swear by WD-40, ATF, Mobil 1, etc. When Clarence Lee recommended air tool oil, marvel mystery oil, engines did not have any silicone parts or even O-rings, just paper gaskets.

The pump and gauge are simply to test that the tank will hold pressure. These engines pump the tank up to 7~10 PSI. Also checks the one-way valve.

And finally there are obscure things that can cause this symptom: bearings (crank has wallowed out the crank case and not sealing), stuck or broken ring, loose head, etc. Completely disassemble the engine and check it out.

If all else fails send it in to Richard Verano at YS parts and service for a rebuild.

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04-22-2018 10:10 PM  28 days agoPost 19
motorrc

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canton ohio usa

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thanks folks for the help

if it doesn't fit, make it fit.

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04-23-2018 01:13 AM  28 days agoPost 20
DS 8717

rrProfessor

Here wishing i was somewhere else

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replace the ring,if it doesnt seal good it will cause the regulator to not function properly because of the blow by......

YOU ONLY LIVE ONCE..IF YOU LIVE IT RIGHT THATS ALL YOU NEED

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HelicopterMain Discussion › YS 80st problem- diaphragm out of adjustment?
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