I have a few questions about my engine on my high wing rc trainer plane?
on the side of the engine it says SC and on the other says 75. but looking through loads of pics it looks like an aps 75. the main problem is it dont run i bought a new glow plug and now it starts but cuts out after 30 seconds or if i give it a bit of throtle. Ive came to the conclusion that it need to be tuned but dont know how please help me i was hopeing to fly today as it is my day off work.

[&o]

Your low-end needle is probably out too far. Read through the OS manual I'm giving you a link for. OS has a good process for tuning an engine. Print it out and take it to the field with you. Takes about five minutes and is much easier with a helper.

http://manuals.hobbico.com/osm/50sx-...1fx-manual.pdf

I'm not sure which style idle jet your carb has, but let's assume it is the standard type. screw it in until it stops and then back it out 2 1/2 turns. Same with the high speed needle. If the idle jet does't tighten after a few turns, the screw it out until it stops and then screw it in until the end is flush with the end of the throttle barrel. You engine should sort of run at this point.

Start it and while leaving the glow starter on, start turning in the high speed needle, slowly until the engine reaches maximum rpm and then starts to fall off. Back the high speed of by a 1/4 turn. If the engine will now run without the glow starter on it, bring it up to full throttle, slowly and re-adjust the high speed valve. Once you have it adjusted, then go to idle, as slow as you can with the engine still running. Now slowly tighten the idle screw ( use a lot of caution here as you are very near the prop - a long thin screwdrive that put your hands out of range of the prop is needed. Again caution ) for maximum RPM. Cut the throttle back again until it just keeps running and adjust the idle again. You should be down to 2500 rpm or less. A tach is really needed but you can do it by ear.

Now go back to full throttle and adjust the high speed valve again. Back to the idle one more time. You should be very close at this point. Now we work on the transistion from idle to high speed. With the engine warmed up, one or tw full minutes at mid range, take the engine down to full idle and let it set for about 15 seconds the jam full throttle.

If it imediatly dies, the idle is set to lean, turn it out 1/8 turn and try again. You want the engine to bark to life as soon as you jam the throttle.

If it sputters and stumbles, the idle is to rich, turn it in by 1/8 turn. Try agin and adjust until it responds well.

When properally adjusted, the engine will jump to high speed with no sputtering or stalling and when you jam it to idle, it will drop down to idle without stalling.

The key to tuning the carb is to do it in small steps. 1/8 turn maximum at a time for the idle jet and one click at a time on the high speed needle. It takes a bit of time for the engine get the new mix, especially at idle. When you are just about there on the idle, 1/16th turn is all you want to move. Also you need your high speed set first, with the idle way rich to get a good adjustment. Screwing with the idle before getting the high speed set will just cause you frustration because you will not get it balanced out correctly.

All this assumes that your tank is set up correctly, right height in relation to the carb, and no leaks. The clunk is free to move, but will not bind in a corner. Same for the fuel lines, no leaks allowed. This allows air to get into the mix. Good fuel is also needed. If your fuel has sat open for a few months, it will not be at it's best. Borrow a tank of fuel from a buddy if you are unsure of the fuel. If it runs good on his fuel, and bad on yours, get a new jug. No difference, you can put the fuel out of mind.

Don

Did anyone else notice that there is no backing plate on the spinner? This seems highly unusual to me, especially on a trainer.

I totally missed that Bruce, but you are correct. Is this they way you are trying to run the engine?? You'll either need to put the backplate on, or take the rest of the spinner off.

Ken

Good one Bruce ,I missed that.

what difference would that make im a newbie

will it make any difference in flight or engine running performance

It could throw things out of balance and even fly apart and pieces hit someone causing injury. Do NOT arbitrarily use/not use parts until you gain more experience. By then you will be able to determine the possible consequences of the act.

daz3nt,
You can run the engine without the spinner without any issues. You do get a couple of small benefits from having one. First is that the spinner actually covers up the root portion of the propeller. This portion of the propeller actually causes drag and can reduce the overall output of the prop. By putting the spinner on you cover up the portion of the prop that causes these problems. Second, with the spinner you get a small amount of flywheel effect which can help the engine run smoother at lower RPM's. Are these factors huge? Not at all. In fact you may not even notice the benefits, so it's not necessary to do it.

But from your pictures you need to decide one way or the other. You will either need to put the backplate on the spinner, or remove the spinner completely. Trying to run the engine like you have in the pictures could be dangerous.

Ken

Thanks everyone before i try again should i use it like this. Pictures following please bare with me.

here is a pic

SC, ASP, Magnum, and at least one more brand name that I'm always forgetting, are all made at the same plant in ShenZhen, China. That's the reason why an SC engine would look like an ASP one.

I have a couple of those spinners. They act as a front washer for the prop. If you look closely at the photos, you will see a line around the spinner. That is wher the nose cone screws on to the base. I'm not a fan of that design as I expect that the nose cone would spin off with the starter.

Don

Guys, I have three different type spinners without back plates. It all depends on the type of spinner. In the first photo, the yellow spinner is made by Ishipla in Japan. I'm not sure who made the red one in that photo as the only markings if embossed from the prop. The second two photos are of a Sullivan Pylon Brand Prop-Loc spinner. Not a back plate to be seen on any of them.

Don

I guess they would work. Don't recall seeing before.

Graupner used to make a spinner like that for electrics.