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10-27-2017 03:32 PM  22 days agoPost 1
Richardmid1

rrProfessor

Leeds, England

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So I've just bought a used heli with a YS91ST in that had been sat for 2 years and it was pretty stiff to turn the motor over at first! I have checked the bearings and there is no excessive rust and the engine looks very clean inside (apparently only had 2-3 gallons through it).

I put the needles back to factory, put in a new OS8 and filled the tank with fresh new 20% Optifuel. To my surprise after priming the engine it fired up first time but died after 3-4 seconds which is kind of normal for a first start. Will it start again?! NO! I've checked the plug, blown any excess fuel out of the plug hole and tried all kinds of low end needle settings from 0.5 to 1.5 turns open! Now it is trying to fire and I can get it to run if I open the throttle WAY up but then the clutch is grabbing!

Oh the pipe is an MP2.

Any help? Never had a YS before.

60% of the time, it works every time!

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10-27-2017 03:43 PM  22 days agoPost 2
JuanRodriguez

rrProfessor

The Villages,​Florida

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Is the plumbing correct between the backplate and the tank ?? Check valve oriented the right way ??

After cranking the motor over for a few seconds, disconnect the vent line from the tank.... you should get a very strong , pronounced "Woooosh" coming from the tank as the pressure is released...... Also, your tank should hold that pressure (before releasing it) for quite a while before relieving the pressure.... if not, you have a leak somewhere....

Lastly, with an engine that's been sitting that length of time, I would replace the diaphragm. That is really the heart of your fuel delivery system and without it working properly, you'll never get the motor running correctly......

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

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10-27-2017 03:57 PM  22 days agoPost 3
crflyer

rrApprentice

Maine

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Great advice above, I would also flush the check valve with some fuel and verify that its opening,the engine operation is showing signs of low tank pressure. These engines require a tight fuel and exhaust system to run correctly.

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10-27-2017 05:21 PM  22 days agoPost 4
Richardmid1

rrProfessor

Leeds, England

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Thanks guys. I forgot to mention the first thing I did when I got the heli was check the one way valve and it was indeed stuck but I blew it through with some wd40 which cleared it and I could then blow threw one way and not the other. The tank is holding pressure well, a bit too well as it swells up like balloon!

Anyway I decided to take the regulator apart and the diaphragm is ok although it did have some dried fuel residue on it which wiped off easily. One thing I did notice is the little rubber part on that tiny valve had deteriorated and the line was hard to blow through even with the valve open. Anyway in the end the rubber part fell out of it's recess and I couldn't get it back in so I've ordered a new regulator. I've also ordered a gasket set, o ring set and new needle valves! £££

60% of the time, it works every time!

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10-27-2017 05:32 PM  22 days agoPost 5
JuanRodriguez

rrProfessor

The Villages,​Florida

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Be careful with the WD40 and the check valve..... I believe the disc inside the valve may be silicone ? If so, petrolium based WD40 and silicone don't play well together......

I would flush it out (or take it apart to clean) using your glo fuel instead....

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

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10-27-2017 07:36 PM  22 days agoPost 6
crflyer

rrApprentice

Maine

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Exactly,WD-40 may not be that friendly. Use Fuel to clean them.
I've learned when check valves stick they never seem to be reliable after cleaning.

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10-27-2017 11:05 PM  22 days agoPost 7
Richardmid1

rrProfessor

Leeds, England

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Actually gt85 but it's had fuel through it now so will be flushed out. If the new regulator etc doesn't fix it I'll be a bit stuck! Any tips on tuning these engines? What are people's needles ending up at for running?

60% of the time, it works every time!

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10-28-2017 04:32 PM  21 days agoPost 8
EEngineer

rrProfessor

TX

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Juan is correct......only use silicone based oils/lubricants on the YS diaphagms, etc.....or else....

Logo 600SXs, 800XX, TDR IIs

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10-28-2017 07:05 PM  21 days agoPost 9
Richardmid1

rrProfessor

Leeds, England

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Ok I'm not sure I got any gt85 on the diaphram but as it's been sat in old dried up fuel for 2 years I thought ide better order a new one.

60% of the time, it works every time!

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10-28-2017 08:36 PM  21 days agoPost 10
JuanRodriguez

rrProfessor

The Villages,​Florida

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Richardmid1
Ok I'm not sure I got any gt85 on the diaphram but as it's been sat in old dried up fuel for 2 years I thought ide better order a new one.
Great idea !

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

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10-29-2017 05:30 PM  20 days agoPost 11
Richardmid1

rrProfessor

Leeds, England

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No idea why you don't get one with a new regulator but there you go.

Will report back once it's all reinstalled. I've got a used Hatori sb19 coming aswell but I think it's for the SR long stroke but it was a good price so worth a try?

60% of the time, it works every time!

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10-31-2017 08:37 AM  18 days agoPost 12
Richardmid1

rrProfessor

Leeds, England

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Update. I made a new seal for that tiny valve under the diaphram and put it all back together and it now runs ok!

Couple of other things I did was to put a new line between the back plate the check valve as it was 9cm and manual says 10cm, not sure how much difference it made though. Also there were burrs inside the barrel at the ends of those channels/veins from machining where the cutter had come out of the end and not taken the burr off cleanly! One of which was ready to drop off and go through the engine! Made in Japan I thought not China! Haha.

60% of the time, it works every time!

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10-31-2017 08:41 AM  18 days agoPost 13
Richardmid1

rrProfessor

Leeds, England

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I also noticed I needed to keep cranking with the glow ignited on for a while till it warmed up so I've ordered an enya3 plug as I've heard they are hotter than the os8 and people seem to have better results with them in the ys's. I may also go to 30% fuel as that is the only percentage it recommends in the manual.

60% of the time, it works every time!

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11-03-2017 08:17 PM  15 days agoPost 14
JWatson

rrKey Veteran

Mustang, OK

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YS91 ST4

I would just like to add that of all the .90 sized engines I have ever ran, I was always impressed with the consistency, smooth transitions, and the amount of power the engine made. The YS coupled with an MP2 made a great combo.

Sure there are newer more powerful engines, but for an all around reliable and constitent engine, the St4 was one of the best IMPO.

Enjoy it! I still have mine!

Jarrett Watson
http://jarrettrc.wordpress.com/

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11-04-2017 01:25 PM  14 days agoPost 15
Richardmid1

rrProfessor

Leeds, England

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Just bought a 91SR off feebay for £40! Bought it for spares as I thought there would be something wrong with it but it looks and feels barely run in! Might be something wrong with the carb or regulator but still a bargain! It's also perfect for the Hatori sb19 I got for £30!

60% of the time, it works every time!

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11-04-2017 04:30 PM  14 days agoPost 16
EEngineer

rrProfessor

TX

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I thought it was "fleabay"...has the name been changed?.....

Logo 600SXs, 800XX, TDR IIs

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11-04-2017 08:47 PM  14 days agoPost 17
Richardmid1

rrProfessor

Leeds, England

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FeeBay due to all the fees for selling stuff! Gumtree is better!

60% of the time, it works every time!

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11-04-2017 08:59 PM  14 days agoPost 18
870heli

rrVeteran

Monson Ma. USA

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The YS91ST is a good engine. I have one in and old T-rex 700 that I run once a year or every other year. I have never had a problem. Flush the check valve and go. I run a OS#8 so far so good.
Good luck with yours.

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11-04-2017 11:22 PM  14 days agoPost 19
EEngineer

rrProfessor

TX

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OS#8
Good plug for YS engines.

Do not ever run a Fox plug or you will regret doing so....

Logo 600SXs, 800XX, TDR IIs

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11-05-2017 01:47 AM  14 days agoPost 20
JuanRodriguez

rrProfessor

The Villages,​Florida

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I have had best luck with the Enya # 3 or # 4 with my YS motors.....

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

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