OS 91 pumped

[dacostad]

I am just completing my Raptor 90SE with a OS 91 pumped engine, is there any reason why I should not also pressurize the tank from the muffler as well? Then manual seems to say run the line from the muffler if you are not using a regulator (which I am), but is not necessary with a regulator.


Thanks


David

[Neriyah]

Well there are pros and cons for both.

Running it with muffler pressure:
Pros
More consistent mixture (I run mine w/o muffler pressure and haven't really noticed any problems with it)
Cons
Corrosive fumes in the tank, have to worry about your clunk lines.
More tubing to worry about, more possible points of failure/leaks

Running it open to atmosphere:
Pros
Just fuel in your tank, don't have to worry about your clunk lines rotting
Simpler plumbing
Cons
Some pumps apparently are more inconsistent than others, need for additional tuning especially with climate changes. Can't say from personal experience since mine has run like a charm even if I fly in an environment that has temperature changes around +-15 celcius from day to day and humidity changes are quite noticeable too.

If you run yous open to athmosphere just make sure your vent line (I used the one where the pressure line connects to) goes below your main tank. Some say you will need a check valve and other say you don't. I havent used one in mine ever and it runs very smoothly. If you have a check valve that will introduce just another possible point of failure, and from what I've heared they do fail alot :).

And ofc these engines take a while to break in. My engine ran like a pig for 2-3 gallons until it smoothed out. Lots of vibrations and seems that R90 frame even amplifies it. My first few flight it vibrated so bad I was afraid that my boom supports were gonna fall off...