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HelicopterEngines Plugs Mufflers Fuel › YS 91 SR unable to build up pressure hence running way too lean ... need HELP!
07-29-2013 10:58 AM  4 years agoPost 1
Zbawer

rrApprentice

Singapore

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Hi boys !

My YS 91 SR has been causing me trouble last weekend :
Right from the beginning when firing up I notice my idling is much higher than normal and so I had to trim the throttle down a bit.
Then when I spool up the response time is much quicker and suddenly I hear the engine screaming and the rotor starts to over speed (confirmed by the GY701 gov monitoring function showing close to 2800 RPM when its normally supposed to be 2100).
Even while flicking in IU1 (therefore activating the governor) did not help.
So within 10-15 seconds I go in TH and post inspection revealed:
• Very little pressure in the tank when opening the valve to release it
• Very hot backplate touching with finger sign of running lean
• AND some nitro residue in the pressure line, between the one-way check valve and the tank !!
I disassembled the one-way valve tried blowing into it and a tiny drop of nitro came out as well !
I now understand the pressurizing system was clogged by this nitro stuck in the check valve but how did the nitro got there in the first place ?
Could it possibly came from the packplate ?
Now that I think of it the pressure nipple down the backplate is right below the crankshaft where the air-fuel mixture enters the cylinder.

Have anyone experienced similar symptoms before ? Which part should I check and eventually replace ?

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07-29-2013 02:42 PM  4 years agoPost 2
Zbawer

rrApprentice

Singapore

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A few more clues while pulling the engine apart :
• My fuel system is perfectly sealed, I could leave it with fair amount of pressure for 15+ minutes and when I opened the valve I heard a good pshiitt sound.
• The muffler (hatori) got flooded with un-burnt nitro fuel … I think here lies my issue. Seriously I think I could extract the equivalent of Italian espresso cup of fuel out of it, some sort of nitro goo. And I did not previously did anything to flood the engine, always take all precautionary measures to avoid this.
What gives ?
I now know there’s something wrong with that engine, but can’t tell where exactly ? The carb ? the regulator ? all internals look perfectly fine, no marks or scores …
I’m stuck !

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07-29-2013 11:11 PM  4 years agoPost 3
airdodger

rrElite Veteran

Johnston USA

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You could have hurt the ring by running lean, the engine depends on the down stroke to build pressure, if your ring is not seated correct it will show here. Start at factory settings, open the idle screw and reset the idle. New plug or you could get false settings. Turn the gov off. No pressure leads me to think you may have a pressure leak. Try another new unopened jug of fuel also. What nitro percentage?

Chris

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07-30-2013 12:29 AM  4 years agoPost 4
MAYHEM

rrApprentice

Motorcity

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Replace the check valve!!!

Just went through this...ended up costing me 2 pistons.
My check valve was only operating at full throttle...I know some say that it's either good or bad, but, mine worked part time. I was getting pressure in the tank, but not enough to keep it running rich

Marshall

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07-30-2013 02:17 AM  4 years agoPost 5
# 1 VIBE USA

rrApprentice

North East,VT

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ck your piston

can u make it go faster

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07-30-2013 02:25 AM  4 years agoPost 6
Zbawer

rrApprentice

Singapore

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Yes I agree a new check valve already is a cheap way to try and sort out my issue.
Don't want to sound pessimistic but I feel there is something else wrong within the engine ...
I was really happy with that YS engine over the past 6 months, producing insane power,but I come to realize I just like OS better, easier to tune and hassle free. Might get my hands on a 91 3D speed sooner than later.

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HelicopterEngines Plugs Mufflers Fuel › YS 91 SR unable to build up pressure hence running way too lean ... need HELP!
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