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HomeAircraftHelicopterEngines Plugs Mufflers Fuel › YS 120SR air bubbles
08-02-2018 03:51 PM  11 days agoPost 1
dweb4

rrNovice

Maryland

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Hello I'm noticing air bubbles in the short fuel line going from the regulator to the carb. I've tried re-tuning, going leaner, richer and still getting air bubbles. The motor runs good but I notice the inconsistency due to the air in the line. Anyone got any suggestions as how to remove them. I have other YS motors from .50 to this one and I never notice air bubbles in the short fuel line before. Thanks

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08-02-2018 04:50 PM  11 days agoPost 2
JLF92677

rrApprentice

Southern California

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Check all 4 regulator assembly bolts are tight (do not over tighten.) If so, check or replace gasket between crankcase and regulator assembly and also check or replace fuel line between regulator and carb.

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08-02-2018 05:14 PM  11 days agoPost 3
datidun

rrKey Veteran

N Ireland

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Not sure what is causing that as never had a YS engine but to prevent it from effecting engine, I would put on a bubbless fuel filter, maybe slight vibration coming from something.

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08-02-2018 05:31 PM  11 days agoPost 4
ticedoff8

rrKey Veteran

Morgan Hill, CA. USA

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I've used YS motors for the last 8 years
All the ones I've used had that regulator on them (60, 91, 96 & 120)
Check all 4 regulator assembly bolts are tight (do not over tighten.) If so, check or replace gasket between crankcase and regulator assembly and also check or replace fuel line between regulator and carb.
^^^ +1

You should also check the regulator's diaphragm for proper fit and integrity (no pin-holes and no gaps around the seat).
EG: I bought a used YS engine where the seller had used a petroleum based after-run oil.
This caused the diaphragm to expand in diameter about 0.5mm. So it wouldn't / couldn't fit back into the diaphragm seat correctly for reassembly.
If I had forced it, there would have been a gap around the seat.
That would have allowed the crankcase pressure into the fuel stream.

Not sure what is causing that as never had a YS engine but to prevent it from effecting engine, I would put on a bubbless fuel filter, maybe slight vibration coming from something
The bubbles are between the regulator and the carb. Not the tank and the regulator.

Believe 1/2 of what you see and none of what you hear.
Fake News will be the downfall of our Republic!

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08-02-2018 06:21 PM  11 days agoPost 5
dweb4

rrNovice

Maryland

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Ok, thanks I'll check all the screws, regulator and diaphragm. I brought the motor from another flyer and not sure what was used to maintain it. I know from the all the YS motors I run there is never been air bubbles in that fuel line.

Also I have a extra regulator from a YS 91SR that ran strong all the numbers match the 120 should I just change them out?

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08-02-2018 09:15 PM  11 days agoPost 6
JuanRodriguez

rrProfessor

The Villages, Florida

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I would just do what has been suggested before parts swapping.....

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

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08-02-2018 11:32 PM  11 days agoPost 7
ticedoff8

rrKey Veteran

Morgan Hill, CA. USA

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I would just do what has been suggested before parts swapping.....
^^^ +1
This gives you an idea of the "root cause" of the issue rather than "I swapped parts and it is all fixed".

But, the regulators are the same.
The 91 & 120 carb's bore and barrels are different. So those are not interchangeable

Believe 1/2 of what you see and none of what you hear.
Fake News will be the downfall of our Republic!

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