Author Topic: OS 40 FP - Problems Solved ! (Read 728 times)

Robin_Holden · « **on:** July 27, 2009, 07:25:52 AM »

Greetings from France.

I posted a thread some time ago about my continuing problems with a ' modified ' FP.40.

I took the recommendations on board regarding the need for more running - in etc. and proceeded to test fly fly last Saturday.

It was a disaster , poor running , only achieving 7,800 rpm with an 11x5 Master Airscrew prop'.
Strangely my similarly modified Tower 40 was brilliant ! [ on the same fuel , with 24% lube and 5% nitro ]

Back to the workshop for a beer , and put the FP on the bench for more testing !

I swapped the NVA / Spray Bar which had TWO holes back to an OS NVA.
I swapped the Tongue Muffler back to the 'portly' standard OS Muffler.
I swapped the plug for a new Fireball Hot plug.

Success at last ! No problems , 8,500 strong reliable 4-stroke with no murmers.

Question therefore is after my ramblings above : Does anyone know why my OS 40 FP dislikes so much the Tongue muffler and the spray bar with TWO holes ?

Would appreciate any comments please. I would mention the ' modifications ' done to my engine were of the First Class variety .

Much obliged ,

Robin [ ex-pat Brit in the Charente full of ex-pat Brits ]

Alan Hahn · « **Reply #1 on:** July 27, 2009, 08:18:22 AM »

Robin,
It isn't clear from your post whether you ran the engine after each of the three changes, or after you did all of them.

But one thing to check is the area of the openings in the tongue muffler compared to the output area in the stock muffler.

Another detail is that the OS spraybars are often narrower than the Supertiger style spraybars. I don't know what the original one was like.

Not sure about the glow plug.

But if the tongue muffler is more restrictive than the stock, that will limit the output (I have run engines where the "throttle" was a flap on the exhaust stack). If the new spraybar is narrower than the previous one, then that too will let the engine rev up more.

Just some guesses.

Ward Van Duzer · « **Reply #2 on:** July 28, 2009, 11:22:52 AM »

Recently ran a four bolt fox .35 (a known runner!) with a new tongue muffler. Sick! No power, no r's! My muffler had two rows of 3/32 " holes. At Randy's request I opened up another row of 6 3/32" holes. Yipeee, I'm in business again with 9100 rpm's

Ward-O

BTW, if you choose to continue to use your factory muffler I would suggest the following. With a hack saw cut off the little stack at the end of the muffler flush. Then ream out the remaining hole another 1/8 of an inch. Will work more better!

W.

Bill Little · « **Reply #3 on:** August 19, 2009, 10:40:32 AM »

Quote from: Ward Van Duzer on July 28, 2009, 11:22:52 AM

Recently ran a four bolt fox .35 (a known runner!) with a new tongue muffler. Sick! No power, no r's! My muffler had two rows of 3/32 " holes. At Randy's request I opened up another row of 6 3/32" holes. Yipeee, I'm in business again with 9100 rpm's

Ward-O

BTW, if you choose to continue to use your factory muffler I would suggest the following. With a hack saw cut off the little stack at the end of the muffler flush. Then ream out the remaining hole another 1/8 of an inch. Will work more better!

W.

HI Ward-O!

The need, or lack there of, for back pressure seems to vary from the old engines to the newer ones, don't you think? It seems the OS 32F needs a lot of back pressure to really run at its best while a Fox 35, OS 35S, McCoy RH, etc., don't like it too much. Or maybe it is a situation of sub piston induction in some cases?

Whatcha' think?

Thanks!
Big Bear

Author Topic: OS 40 FP - Problems Solved ! (Read 728 times)

Robin_Holden

OS 40 FP - Problems Solved !

Alan Hahn

Re: OS 40 FP - Problems Solved !

Ward Van Duzer

Re: OS 40 FP - Problems Solved !

Bill Little

Re: OS 40 FP - Problems Solved !