Thread Tools
Apr 10, 2016, 07:09 PM
Registered User
Thread OP
Discussion

HELP Needed: OS 40 FS Tuned Pipe tuning guidance


I just got this 40 size plane not sure what it's called but it's a low wing with retracts. Anyway Motor and carb was sized. I finally got it all trimmed out. I took the carb and cleaned it out thoroughly and unsized the motor with some penetrating oil etc... So the hard part for me is getting it tuned properly. I got a new A8 plug for it. I got it idling and adjusted the highend till it the pitch changed then back it off 3 clicks. So it should be nice and rich setting. Here is my problem.

When I transition from about 1/2 throttle to WOT it dies out the engine just cuts out. Does that mean it's RICH or LEAN? Do I adjust the needle in or out or do I adjust the mixture (carb side) screw in or out?
Sign up now
to remove ads between posts
Apr 10, 2016, 08:16 PM
Registered User
What is a sized engine??

Sounds like your low end is lean. You should set the high end first then go to the idle adjust. Back and forth til you get it right.
Apr 10, 2016, 08:30 PM
Registered User
Thread OP
Quote:
Originally Posted by datsunguy
What is a sized engine??

Sounds like your low end is lean. You should set the high end first then go to the idle adjust. Back and forth til you get it right.
I did I set the high end first WOT kept leaning (needle in) until it the RPM's dropped then backed it off 3 clicks.

It's an OS 40 FS Max with a tuned pipe.
Apr 10, 2016, 08:39 PM
GloBroz PowerLab
1QwkSport2.5r's Avatar
It's still too lean. Tuned piped engines need to be set much richer than an engine with a regular muffler.

When you lean the needle until the rpm drops, you need to richen back up to the point just before it sagged and go richer yet from there. A good figure is set your main needle for about 800rpm rich from peak when using a full wave tuned pipe. You should set your idle a bit fatter than normal too so when you drop from high rpm to idle it doesn't burn the plug out. It's not uncommon for this to happen.
Apr 10, 2016, 09:21 PM
Registered User
Thread OP
Thanks for the help guys
Apr 10, 2016, 10:16 PM
Registered User
It's the low end that's too lean

At idle pinch the fuel line. If the low end is set right it should speed up a bit before it slows down and quits. If it doesn't it's too lean.

Also, FS on an OS engine indicates it a four cycle. They don't use tuned pipes.
Apr 11, 2016, 12:34 AM
Registered User
Reginald's Avatar
carefull carefull...before you know it we will have an endless tread about the fact that there are OS fourstrokes using a tuned pipe after all ending up with pics of some Ukranian tractors...
Apr 11, 2016, 03:33 AM
Closed Account
Quote:
Originally Posted by datsunguy
Sounds like your low end is lean. You should set the high end first then go to the idle adjust. Back and forth til you get it right.
Don't think so, because:

Quote:
Originally Posted by Fidy$Trainer
When I transition from about 1/2 throttle to WOT it dies out the engine just cuts out.
Basically, Qwk has it right, the high speed needle is way too lean, as the engine revs up in the air a lot more on a correctly tuned pipe, than an engine with a normal muffler....

BUT: A tuned pipe is a bit of an on/off afair: the lenght is depending on the RPM the engine can achieve, and has to be shorter for higher RPMs.

A too short pipe tends to overheat the engine, and when you are running half throttle on a pipe tuned for full throttle, the pipe is basically too short for the RPM that you are running and thus the engine tends to run hotter than usual.
Bottom line is, you actually don't want to run prolonged in that mid-throttle range, and it MIGHT proove impossible to get that particular response (transition from 1/2 to full throttle) 100% right, you might have to accept a compromise of for example a slightly too rich idle or a less than immediate transition.

You probably also still have to tune the pipe length, and that has influence on High speed needle setting required, which in turn MIGHT influence LSN required....
Pipe length and final HSN setting have to be determined in flight, you cannot do that on the ground.
Apr 11, 2016, 06:11 AM
I bail out, anywhere, anytime
Taurus Flyer's Avatar
Quote:
Originally Posted by Reginald
carefull carefull...before you know it we will have an endless tread about the fact that there are OS fourstrokes using a tuned pipe after all ending up with pics of some Ukranian tractors...
With so many specialists solving this problem is a whistle of a penny, here we go.

Quote:
Originally Posted by Brutus1967
Don't think so, because:



Basically, Qwk has it right, the high speed needle is way too lean, as the engine revs up in the air a lot more on a correctly tuned pipe, than an engine with a normal muffler....

BUT: A tuned pipe is a bit of an on/off afair: the lenght is depending on the RPM the engine can achieve, and has to be shorter for higher RPMs.

A too short pipe tends to overheat the engine, and when you are running half throttle on a pipe tuned for full throttle, the pipe is basically too short for the RPM that you are running and thus the engine tends to run hotter than usual.
Bottom line is, you actually don't want to run prolonged in that mid-throttle range, and it MIGHT proove impossible to get that particular response (transition from 1/2 to full throttle) 100% right, you might have to accept a compromise of for example a slightly too rich idle or a less than immediate transition.

You probably also still have to tune the pipe length, and that has influence on High speed needle setting required, which in turn MIGHT influence LSN required....
Pipe length and final HSN setting have to be determined in flight, you cannot do that on the ground.
TF


Quick Reply
Message:

Thread Tools