HELP! OS .30 Stunt will not rev up to proper speed ????

[frank mccune]

    Hello All:

    I test ran my "new" OS .30 Stunt today and it produced these rpm figures on a 10x3 prop:

    5000 rpm with 703 muffler

    8000 rpm with no muffler

    The fuel is 75% alky and 25% castor oil.

    Tried two different plugs.

    Needle valve has 90degrees latitude between too rich and too lean.

   The nva is a ST
 
   Compression is good hot or cold.

   The p&c are installed correctly.  It does seem to run like they are installed backwards.

   The exhaust sound is very muffled and quiet.

   There are no leaks from the engine and the engine appears to be in great nick.

   I doubt that the 10x3 prop is too much of a load for this engine as it produces the same load as a 9x5.

   Low rpm and a very subdued exhaust sound should tell me something but I am not smart enough read these indications.

   Any suggestions as how I can get this engine ready to run on a Stunter? 

                                                                                                                              Tia,


                                                                                                                              Frank McCune

                                                         

   

[RandySmith]

What size is the venturie?  and double check the sleeve, make sure the rod is in correctly, use a fuel with a small to half synthetic oil, and it will run and needle better with 5 or 10% nitro

Randy

[frank mccune]

     Hi Randy:

     Thanks for the reply.

      The venturi measures .281". I checked the p&c to be certain that it is installed correctly and it was.  I think that the rod will only fit one way, the correct way.  I may be wrong but it looks to be installed correctly.  What is the indication that the  rod has been installed backwards?

     I do have some 10% nitro fuel that has 22% half and half oil that I will try tomorrow.  I do not think that I will see much gain in performance with the otter fuel but what do I know?

     Do you have venturm in stock for this engine that may be a bit better for a stunt engine?

     A friend of mine flies this engine complete with a muffler and it is a sweet running engine!

                                                                                                  Be well my friend,

                                                                                                  Frank

[RandySmith]

     Hi Randy:

     Thanks for the reply.

      The venturi measures .281". I checked the p&c to be certain that it is installed correctly and it was.  I think that the rod will only fit one way, the correct way.  I may be wrong but it looks to be installed correctly.  What is the indication that the  rod has been installed backwards?

     I do have some 10% nitro fuel that has 22% half and half oil that I will try tomorrow.  I do not think that I will see much gain in performance with the otter fuel but what do I know?

     Do you have venturm in stock for this engine that may be a bit better for a stunt engine?

     A friend of mine flies this engine complete with a muffler and it is a sweet running engine!

                                                                                                  Be well my friend,

                                                                                                  Frank

The OS 30 S  is indeed a sweet little engine, and the ones I have and have seen put out good power. A couple of things, you really need a large venturie "if"  your going to use the OS 703 muffler with the tiny outlet, mine have .295 to .312 s sizes in them. IF you run an open/normal size muffler or a tongue muffler  you need to run a .265 to .281 size,  The 703 is really restrictive and likes a large venturie, OS installed these in them factory. T
Jetstream muffler can also use the smaller size.

Randy

[Gerald Arana]

   Hello All:

    I test ran my "new" OS .30 Stunt today and it produced these rpm figures on a 10x3 prop:

    5000 rpm with 703 muffler

    8000 rpm with no muffler

    The fuel is 75% alky and 25% castor oil.

    Tried two different plugs.

    Needle valve has 90degrees latitude between too rich and too lean.

   The nva is a ST
 
   Compression is good hot or cold.

   The p&c are installed correctly.  It does seem to run like they are installed backwards.

   The exhaust sound is very muffled and quiet.

   There are no leaks from the engine and the engine appears to be in great nick.

   I doubt that the 10x3 prop is too much of a load for this engine as it produces the same load as a 9x5.

   Low rpm and a very subdued exhaust sound should tell me something but I am not smart enough read these indications.

   Any suggestions as how I can get this engine ready to run on a Stunter?  

                                                                                                                              Tia,






Frank, You said the P/L is in correctly. Ok, is this a baffled engine? Is the baffle in correctly; baffle away from the exhaust? Yes, the head would have to be on backwards too.
Personally I'd take this engine apart and check everything. Does the crank spin in the CC bearing without binding? Is the wrist pin free? All gaskets sealing? Does it have good compression?

And really, is the liner in correctly??? That'd be my first guess. As for the con rod, it (may) has/have an offset to it so the counter weight doesn't hit it when rotated.

And with that, I'm out of ideas. I sure hope you find the source of the problem and let us know.

Cheers, Jerry

PS: Is your Tach working properly?

                                                                                                                          
                                                        

  

[FLOYD CARTER]

The complaint about "quiet" sounds like restrictive muffler.  Open up the muffler exit hole.  First, run it open exhaust for a benchmark.

F.C.

[Air Ministry .]

Its possable to fit the sleeve ( cylinder liner ) backward . It may have been awkward to install upside down . 

I got a K&B 40 that had the piston ports bored in he wrong side of the liner , installed so the ports matched the piston ports , the
transfer & exhaust were transposed .I just flung it in with piston ports non functioning .

If you pull the head , as the piston goes up , it should close the transfers before the exhaust .

p.s. got some diesel , with good oil . Time to test the ETAs ,if its not hailing or snowing ,  )

[Bill Johnson]

Frank,
It really sounds like something's not put together right. My OS 30 converted from an old RC engine, with a 7MM (.284) venturi, old OS NVA and the 703 muffler installed turns over 10,000RPM with a TF 9X5. It clocked maybe 1000RPM more without the muffler but I didn't write it down. Fuel is 10% nitro, 11% synthetic and 14% castor (GMA 10/22 W/5 oz castor added).

The OS 703 is also on an OS-S 35 with no problems and, the OS 843, a newer bolt on muffler has the same exhaust opening.

P.S. Don't necessarily trust any index line on the sleeve. I took one apart recently and it had the index mark at the rear where it normally goes but that was wrong. The transfer port is the lower of the two on the sleeve.

[frank mccune]

       Hi All:

       Problem solved! The cylinder was indeed turned with the ports in the incorrect position.  Corrected my blunder and now the engine runs very well.  Sometimes, I just over look the obvious! Old age may be creeping up on me! Lol

                                                                                                              Thanks for all of the replies,

                                                                                                              Frank

[RandySmith]

hi Frank
I asked you to double check the sleeve because  I thought that was what it was, that has happened  to many people, it is a common occurrence.
Glad your back and running, did you use the  new hard rod I sent you?

Randy

[frank mccune]

    Hi Randy:

    Good to hear from you.

   No, I did not use the hard rod.  I was saving it for a  .35 which in retrospect seems to be foolish.  At my age, I do not buy new shoes anymore!

   Do you have a Jetstream muffler to fit this engine?

   Have you considered that the smoother running of the .30 vs. the .35 may be due to the fact that the .30 is running a lighter piston in what otherwise would be a .35 engine? I think that the Fox .29 Stunt appeared to be a bit smoother running engine than the Stunt .35.  Perhaps it is all in my mind. Lol

                                                                                             Be well my friend,

                                                                                             Frank