SC 25 Nitro Engine Setup

by Clive

New to using Nitro engines, so got myself a Seagull Jumper 25, with SC 25 nitro
engine.

Put it together but the instructions provided for the engine are very sparse.

From looking around the web i am assuming that the screw at the opposite end of the carb to the throttle is the needle valve.

There are another 2 screws on the carb and again i assume that the spring mounted one is the low speed?

This one when screwed in forces the throttle to open ?

Can you offer a more precise procedure before i attempt to start this engine.

Thanks

Clive

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SC 25 Nitro Engine Setup

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Aug 24, 2009
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SC 25 engine
by: Matt

Hello Clive,

Can you provide a pictures of this engine? A picture is worth a 1000 words...

I'm not really familiar with this particular brand of engine. Our friend Micheal from Oz provided some pretty good info on SC engines in general here.

Most engines have the low speed needle screw located on the same side of the carb as the throttle arm. However, some engines have air bleed screw on the carburetor.

It is important to know which one you have because turning in a needle valve leans the mixture while turning in an air bleed screw causes the engine to pull in more fuel making it run more rich.

I'm guessing the SC engines have low speed needles and not air screws. But this is only a guess.

Scroll down to the picture of low speed needle on this page.

On most engines there is a screw on the carb called a throttle stop screw. This screw rides in a groove cut in the barrel that makes the barrel move side to side when the throttle moves in order to control the low speed.

The Throttle Stop Screw is for setting the minimum idling speed. If the engine runs too fast with the throttle closed, this screw lets you close the opening a bit a low throttle, or vice versa.

I take it your manual doesn't have a good diagram of the parts?

Scroll down to the bottom of this Evolution Engine Manual for an exploded view of the parts.

This is not your engine of course, but most all engines pretty much have the same parts and this exploded view should help you a bit.

If you have some pictures please send them. I've never really had to "put together" any engine. All of mine have been assembled from factory.

I hope this post helps you with your SC 25 engine. If you still have questions after this long winded post please ask!

Thanks!

Matt

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Aug 24, 2009
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Submitted by: Matt

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Hello Clive, Can you provide a pictures of this engine? A picture is worth a 1000 words... I'm not really familiar with this particular brand of engine. Our friend Micheal from Oz provided some <a href="http://www.hooked-on-rc-airplanes.com/sc-46-nitro-aircraft-engine.html">pretty good info on SC engines in general here</a>. Most engines have the low speed needle screw located on the same side of the carb as the throttle arm. However, some engines have air bleed screw on the carburetor. It is important to know which one you have because turning in a needle valve leans the mixture while turning in an air bleed screw causes the engine to pull in more fuel making it run more rich. I'm guessing the SC engines have low speed needles and not air screws. But this is only a guess. Scroll down to the picture of low speed needle on <a href="http://www.hooked-on-rc-airplanes.com/nitro-engine-tuning-tips.html#adjust">this page.</a> On most engines there is a screw on the carb called a throttle stop screw. This screw rides in a groove cut in the barrel that makes the barrel move side to side when the throttle moves in order to control the low speed. The Throttle Stop Screw is for setting the minimum idling speed. If the engine runs too fast with the throttle closed, this screw lets you close the opening a bit a low throttle, or vice versa. I take it your manual doesn't have a good diagram of the parts? Scroll down to the bottom of this <a href="http://www.evolutionengines.com/ProdInfo/Files/9155_EVO-NTNXManualUpdate.pdf" rel="nofollow" target="_blank">Evolution Engine Manual</a> for an exploded view of the parts. This is not your engine of course, but most all engines pretty much have the same parts and this exploded view should help you a bit. If you have some pictures please send them. I've never really had to "put together" any engine. All of mine have been assembled from factory. I hope this post helps you with your SC 25 engine. If you still have questions after this long winded post please ask! Thanks! Matt

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Aug 25, 2009
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Here's a picture
by: Clive

Hi

As requested please find attached a picture of the SC25

As you look at the pic on the right is the throttle link, at the other end
is I will assume the throttle needle valve.
To the left of the carb air intake is a spring screw which as adjusted opens
the barrel in the carb. To the right is another screw (difficult to see) ??

Hope this helps.

Clive

Aug 25, 2009
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Not sure about the second screw on the carb of your SC 25?
by: Matt

Hello,

I placed the picture you submitted at the top of the post.

I labeled the high speed and low speed needles.

To be completely honest with you, I've never had a glow engine that had two screws on the carburetor like your SC 25.

All of the engines I've had only has the throttle stop screw that serves two purposes. One purpose is to set the minimum opening of the carburetor. The second purpose is that it sits down in the spiraled groove which causes the carb barrel to move left to right when it is rotated by the throttle arm. This in turn controls how much fuel gets to the engine at idle...

I am only guessing, but I am thinking maybe the SC 25 has a screw for each of these functions. One screw for a throttle stop and one screw for guiding the barrel.

Hopefully Michael from Oz will chime in as I am sure he knows for sure.

I am really curios myself as to what this second screw is... Guess you learn something new every day!

Matt