I hope this is the right place to post this. First off, my 91 will not idle below 3200 rpm or it just dies. I have been through carb, adjusted valves everything I can think of this one has me stumped.
The tank is center to the nozzle, the motor is mounted at a 90 on a funtana x 50. Has new fuel line, I have tached it out at full rpm, then to idle to make the adjustments. Also it has a F plug, and I have tried 3 different ones, the fuel line is also short and direct.
Oh and one more thing the motor is not new and use to run great.

What gives?[sm=punching.gif]

Might want to check the OS engine forum and ask Bax....Rog

check the O ring on the carb manifold or the gasket at the point where it bolts to the head

Ha, I found out what it was a broken exhaust valve spring HOORAY I was ready to throw that motor away.
Thanks everyone.

Just two related questions:

1) Is it compulsary to have a Tach to tune a 4S engine? I havent actually flown my 91FS yet but have set it up by sound and a IR gun. Have set the idle just a bit above the point where the engine starts sputtering and it will surely speed up in flight

2) Due to model restrictions, the carb is below the tank, it is not possible to lower due to throttle rod routing. It is a good 1.5" above carb centre. Engine is inverted. Is that very critical?

3) On my veteran Top star model, the firewall actually deflects when going from idle to full throttle even with the engine off. You can actual see it deflect. I already tried resetting the throttle position but it doesnt help. There is no load on the servo at either end as there is no chatter or buzzing. Is this expected?

Ameyam

1 - No. Some people say that they need a tach and insist that others do the same, but I've been using OS 4-strokes (and others) for over 20 years and have never needed a tach to dial them in.

2 - Aligning the tank on the carb is ideal, but far from critical. If it were, you'd never be able to fly anything but straight and level, right?

3 - This does not sound right. Are you saying that the throttle pushrod is causing the firewall to deflect? Can you describe it further?

Something is sure deflecting. When I advance throttle the engine assembly noses up and back down when I retard. Note this is without engine running. My throttle servo does not buzz or chatter however, I adjusted it that way since I have a sliding adjustment rather than a Z-Bend on the same. It is either the FRP mount or the firewall that is deflecting.

I will chk once again tomorrow and report back with some pictures. As I am still recovering from a bad flu I dont yet have the stamina to wrench open the prop to open the cowl, just enough to keep posting as I am doing today

Ameya

Bummer, I hope you get well soon. And yes, please post some pics when you are feeling better

OK, I am feeling a bit better today and opened up the plane to look at the engine. I am posting 3 videos here, in the first you can see the deflection of the engine with the cowl on and in the second and third, without the cowl. It is the FRP mount that is deflecting. Can you suggest what to do?

Should I replace and with what. I was thinking the Dubro motor mount for the FS-91SII engine

http://www3.towerhobbies.com/cgi-bin...?&I=LXD632&P=7

They say that these have rubber fixture that prevents engine vibration going to the airframe. What do you think?

How to upload mpg files?

Ameyam

Upload the files to YouTube and post a link here

Thy these

http://www.youtube.com/watch?v=wlCYZ_KBPr0

http://www.youtube.com/watch?v=6l2_gVvvgFY

http://www.youtube.com/watch?v=cH9nKEVxYGM

Thanks