4 stroke mods for PA?

I've got a few questions for the 4 stroke users out there... Did you replace the R/C throttle with a simple venturi/needle valve? Do they get easier to start after they are broken in? (I've just purchased a Magnum XL .30RFS and it is nearly impossible to start by hand). Are they sensitive to mounting orientation (i.e verticle, horizontal, inverted, etc.)? Are they sensitive to fuel tank location w.r.t. the needle valve? Do the same rules of thumb for positioning the fuel tank apply as for the 2 stroke engines?

Thanks.

>I've got a few questions for the 4 stroke users out there...
>Did you replace the R/C throttle with a simple
>venturi/needle valve? Do they get easier to start after they
>are broken in? (I've just purchased a Magnum XL .30RFS and
>it is nearly impossible to start by hand). Are they
>sensitive to mounting orientation (i.e verticle, horizontal,
>inverted, etc.)? Are they sensitive to fuel tank location
>w.r.t. the needle valve? Do the same rules of thumb for
>positioning the fuel tank apply as for the 2 stroke engines?
>
>Thanks.

The magnum is a ringed engine, they take awhile to break in. You will find that the compression will increase the more you run it. I think most of the R/C carbs are replaced.

I believe I am correct in that many 4 stroke flyers use an electric starter. Some don't after they get use to the engine and it is well broken in. 4 strokes will start and run backwards very easy and it isn't good when the intake becomes the exhaust.

Ultra hobbies makes a venturi conversion for the Saito 56 and 72 but I don't think conversions for other 4 strokes are readily available. Most just wire the throttle open or use some means to hold it at a specific opening depending on if they need full power or not.

Hope this helps..

H: Get an electric starter. Starting 4-strokes motors by hand is a major pain in the you know what. As Bob said they start backwards quite easily, and that is no fun. They rarely start backwards with an electric starter because it keeps the motor spinning until it is running.

Yes, a 4S motor is sensitive to tank height just like a 2S motor is. The same rules seem to apply. We (ultra Hobby Products) currently make a manifold/venturi setup for the Saito 56 and 72, and have one coming out shortly for the Saito 40; but we haven't had any demand for the Magnum engines yet. Each motor has to have a dedicated setup, so it is quite labor intensive.

As for my overall impressions of 4S motors; so far I am quite happy. They provide plenty of power and it feels like you have all day during the maneuvers. We started running them by tuning the motor up to its peak rpms then backing the needle off just a little bit. Now, I have my Saito 56 backed quite a way off peak, and am flying 5.5 - 5.6 lap times. The plane (Sportster) really flies nice at this speed, and there is plenty of power. I don't know how many rpms I am below peak, as I have stopped using a tach and just go by how it sounds.