engine help

[nick.m]

i bought a second hand trex 700 with a ys91 pumped motor, had very little use, converted the heli to flybarless and took it for its frist flight today.. ive not flown in 7 years so was a little nervous, it started and seem to run fine but there was tons and tons of smoke, more than i remember to be normal, after 5 mins of flying the motor just cut out, it restarted but died after 10-15 seconds, then it got to the point it would run while you were spinning it over with the starter but would stop instantly, the plug is quiet black and it was a new one,, is it too rich and does any one know the standard needle settings for this engine

[banshee rider]

https://www.manualslib.com/manual/658651/Ys-91sr.html

[nick.m]

thank you

[ticedoff8]

If you use the manual's suggestions for the initial needle settings, that will guarantee that the engine will run and not burn out, but it will be too rich to fly.
Use the manual's settings as a starting point and then lean them 2 or 3 "clicks" at a time until it is flying reliably and strong.

[nick.m]

ok so i set it the manual , fired it up last night but unless i have a pretty high tickover set it runs for 20 seconds and just dies, i did lean out the idle slightly but doesnt seem to make any difference

[Andy from Sandy]

I have only ever encountered one engine that when started from cold would tick over for ever without stopping.

Most engines oil up and stop unless the throttle is blipped from time to time.

Going back some to the OS 50 it was generally accepted the idle be set just a little rich that then required constant blipping to keep it running. Once it had been run up and flown and got hot then it would tick over.

[nick.m]

well i did run it for a while so it was warm but no where near the temprature it would reach flying, when raising the throttle from idle it does really struggle to pick up like its way too rich with tons of smoke, do i lean the idle or the hover needle

[banshee rider]

I would lean both
the idle only a little about a screw driver thickness
the hover probably 3 clicks to start

BUT only change one at a time test it
then change the other

There is really no way for any one to tell you how much without seeing and hearing it

Are the settings at the rich side of the instructions or at the leaner side

Hover1.75 open1.75 ~1.50

Low1.25 open0.75 ~0.50

Full1.25 open1.25 ~0.75

[ic-racer]

This motor was in a flybar helicopter? I don't see how the carb won't be gummed up after 7 years, even if you were using synthetic.

[nick.m]

Originally Posted by ic-racer

This motor was in a flybar helicopter? I don't see how the carb won't be gummed up after 7 years, even if you were using synthetic.

when i bought the heli it looked like it hadnt had much use, i pulled the motor out to fit a new clutch , not because it needed it i was bored and had a brand new uprated clutch, the engine and carb looked spotless

[nick.m]

Originally Posted by banshee rider

I would lean both
the idle only a little about a screw driver thickness
the hover probably 3 clicks to start

BUT only change one at a time test it
then change the other

There is really no way for any one to tell you how much without seeing and hearing it

Are the settings at the rich side of the instructions or at the leaner side

Hover1.75 open1.75 ~1.50

Low1.25 open0.75 ~0.50

Full1.25 open1.25 ~0.75

i set them to the leaner side of them settings

[nick.m]

ok so took it out tonight with slightly leaner factory settings, started and was flying fine, im only a sport flyer,, half way through the full tank i noticed that the smoke had got a lot less so landed richened it up a little but then it wont start, leaned it back out and it started fine , took off and 30 seconds into the flight it cuts out and the motor is megga hot, let it cool down richened it up again but now it wont run again, just cant get my head around it

[banshee rider]

Sounds like you may have an air leak causing it to go lean
check all your lines and where the pump bolts up to the engine
also check the lines in the tank

[nick.m]

its now dead lol, snapped con rod

[Sky_]

Hello,

I also followed this thread a little. It was clear from the start that this engine would break down very soon. There is a great deal of variation and manufacturing tolerance at YS. Therefore it is for pilots who do not want to forego the performance potential of a YS engine to install an OS Carburetor. Then reliable operation is possible over the long term. Sure you could adjust the throttle barrel on a YS engine so that it works well.

There are two providers for the adapter:

https://rc-carbonstore.com/OS-61-Car...120-Conversion

Powa Tune Kit - Custom Machined Parts

Some info:
https://www.helifreak.com/showthread.php?t=848251

[ticedoff8]

Hello,

I also followed this thread a little. It was clear from the start that this engine would break down very soon. There is a great deal of variation and manufacturing tolerance at YS. Therefore it is for pilots who do not want to forego the performance potential of a YS engine to install an OS Carburetor. Then reliable operation is possible over the long term. Sure you could adjust the throttle barrel on a YS engine so that it works well.

There are two providers for the adapter:

https://rc-carbonstore.com/OS-61-Car...120-Conversion

Powa Tune Kit - Custom Machined Parts

Some info:
https://www.helifreak.com/showthread.php?t=848251

I did this conversion on 2 of my YS 120SR-X. It is a good conversion, but quite costly.

Given the OP's minimal nitro experience and the level of repair required to get the YS 91 running again, I'd recommend making a clean break and finding a used OS 91 variant so he can get back in the air with minimal down-time.

[banshee rider]

I Have 2 YS engines right now that have at a minimum of at least 30 gallons thru each of them !

There a good high quality engine you just cant crank on the needle valves as much
there needles are much more sensitive than a OS

The conversion to a OS carb does make them more user friendly but it is not a must do

[Trailbilly]

Same motor, My low is at .5 out . Sooty but it sounds like it’s low on compression, visual check the cylinder for scores if need be replaced, a main has the parts .

[nick.m]

ok so stripped it down today, looks like the piston siezed in the barrel and its broke the bottom of the conrod where it sits on the crank.... i do have a fair bit of nitro engine experiance all be it mainly with single needle carbs and did have the same engine in a 700 i owned 7 years ago that ran faultless, i bought this heli second hand and allthough the motor looks like its had very little use all my efforts could not get it running right, allthough there was always loads of smoke it was always hot even though i was never much above half throttle, new motor and pipe on its way