4-Strokes : Muffler Pressure ?

[Robin_Holden]

Greetings guys , and please excuse me if this has been covered before.

I'm new to 4-strokes. I do have a [factory] Saito 56 in C/L guise. After my usual very careful running - in process I'm now test flying.

I had been advised to run my Saito with muffler pressure to the uniflow tank. [ Connected to the uniflow pipe of a Brodak metal tank ].

I was using a 13x6 prop' , 20% total lube' [ 18% synthetic / 2% castor ] with 5% Nitro'.

I couldn't get a decent needle setting on the ground , it 'burbled' and stopped after about 30 seconds.

I took off the pressure tubing. Set the needle at it's usual setting , around 2 and a half open.
Started her again , no problem ! Tuned to give a tad rich 8,400 and it flew in a solid , reliable typically Saito run  !!

Happy Days  !

So guys , is it pressure or no pressure ....That is the question ? Sounds like Shakespeare's Hamlet from school days !

Maybe it's just my engine. Any contributions will be much appreciated.

Robin.
 

[Bill Little]

I've been told to use muffler pressure but with a plastic clunk tank.  Not sure if metal tanks would make a difference, but all I have heard is "use a clunk tank".

Bill

[John Christensen]

I like to use muffler pressure with the Saito .56, because it is easier to prime the motor. I turn the prop over 4 complete compressions and usually get a good start. The first start of the day when it has not been run for a few weeks (months) may take a greater prime. The one problem with using muffler pressure is that the engine can run backward. Which is why I aways use an electric starter. I do use a plastic tank setup per Brad Walker's instructions.

[Joe Yau]

Hi Robin,

I've used both set ups in the last few years.  and a 4-stroke user in our club had some good success with uniflow set ups with clunk tank as well.   I also find with muffler pressure its much easier to prime the engine.  Especially when the carb is buried deep inside the cowl, and no finger access is possible.  even if there is, the choke screw gets in the way. ( forcing air through the uniflow vent works too )  I fly all year round, and at near 0 degree C temperature, it is necessary to keep my finger over the muffler exit for a few times for priming like riding the throttle.. when its about to die, you plug it again.. till its able to idle on its own. (This is only necessary on the first flight, or when its been sitting a while)  so, no opening up the needle valve is necessary which could mess up the run setting.  otherwise it'll just fires up then quits over and over.. till its warm.   I also use an electric starter to prevent from running backwards.   The run with Muffler pressure is quite predictable with a slight speed increase towards the end, which I like for the OH-8 etc.