What are all these screws on the engine for?
08-26-2002, 12:23 PM
#1
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What are all these screws on the engine for?
Hello,
I'm completely new to this RC plane stuff. I've acquired my Dad's old High Wing Trainer. I do beleive it did fly once!
Anyway, the engine was all stuck so I took it apart and cleaned it. Put it back together and realised that I didn't take not of the adjustment screw positions....
Okay, it's a OS Max 35 FP (About 15 years old?) Theres a big screw which seems to adjust the fuel and two other screws (one vertical and one horizontal) attached to the air intake thingy.
What does each of these screws do?
I've had it running for about ten secs - kinda like this....
.....twenty minutes of prop turning and random screw fiddling - Engine starts and runs for ten secs. Adjust all the screws randomly (ofcourse! I'm a newbie!) and now I can't for the life of me get it fired up again.
I obivously need help (In more ways than one)
Cheers in advance
I'm completely new to this RC plane stuff. I've acquired my Dad's old High Wing Trainer. I do beleive it did fly once!
Anyway, the engine was all stuck so I took it apart and cleaned it. Put it back together and realised that I didn't take not of the adjustment screw positions....
Okay, it's a OS Max 35 FP (About 15 years old?) Theres a big screw which seems to adjust the fuel and two other screws (one vertical and one horizontal) attached to the air intake thingy.
What does each of these screws do?
I've had it running for about ten secs - kinda like this....
.....twenty minutes of prop turning and random screw fiddling - Engine starts and runs for ten secs. Adjust all the screws randomly (ofcourse! I'm a newbie!) and now I can't for the life of me get it fired up again.
I obivously need help (In more ways than one)
Cheers in advance
08-26-2002, 12:33 PM
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What are all these screws on the engine for?
Carry the engine to an r/c hobby shop or flying field and get some advice,wrong fuel or running engine to lean will ruin it,on screw is throttle stop,the other is probably low speed adj,or the screw that holds the carb in place
Have a goodun,John
Have a goodun,John
08-26-2002, 01:27 PM
#3
What are all these screws on the engine for?
The big screw is indeed, fuel flow. Screw it all the way in, then back it out 3 or 4 turns. The other horizontal screw is probably low-end air adjustment. This will adjust the fuel mixture when at idle. The vretical screw is probably a throttle stop to regulate how much the barrel opens and closes.
08-26-2002, 02:59 PM
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What are all these screws on the engine for?
MinnFlyer got you started -- identified the screws. TerrellFlyer gave you an excellant suggestion -- hopefully that resource is available to you.
As MinnFlyer stated, the large screw on the left side of the carburetor (left side if you were sitting in the airplane and the engine was upright) is the air-fuel mixture screw. It is mainly used to set the fuel-air mixture for full throttle. A good starting value for this needle is 3-4 turns out (counter clockwise) from full close, that will give you a rich setting and prevent the engine from over-heating.
The screw on top is the idle stop screw and is strictly a mechanical stop -- when you close the throttle (throttle arm is on the oposite side of the carburetor from the large screw.) look down in the carburetor throat to see if it is totally closed or partially opened. You want it to be almost totally closed with just a slight opening crack -- about the width of a hair. You achieve this by adjusting the throttle stop screw.
The 3rd screw is the air bleed screw (in some engines it is also an air-fuel mix screw). It's primary purpose is to adjust the engine idle. Try a starting point about 2 turns out from stop.
Now you should be able to start the engine. Choke the carb by opening the throttle to full, place your finger over the opening and turn the prop counter-clockwise about 3 times. Bring the throttle down to idle stop and then back up a couple of notches. Put a glow starter on the glow plug. Slowly turn the prop counter-clockwise until it gets hard to turn. Flip the prop counter clockwise -- it should start after 1 or 2 flips.
If after several attempts you get no indication the engine is trying to start check the status of your glow plug -- replace if you cannot get a glow from it outside of the engine.
If the engine starts you should be able to slowly advance the throttle to full. It should now be blubbery rich and ready for adjustment. Slowly close the large screw clockwise a few clicks at a time. Listen for the rpm, after each adjustment it should get faster and faster -- stop when it starts to decrease instead of increase, then back off a few clicks. If you have a tach adjust to about 400rpm below max. This is the way you should always fly the engine -- the extra 400 rpm is usually made back up when the airplane is in the air and if you didn't have it on the ground it would lean out on you in the air -- stall and possible engine damage.
Now bring the throttle down to idle. Pinch the fuel line to the carb until the engine quits. If it surges just before it quits it is too rich -- close the airbleed screw 1/8th turn clockwise and restart. Repeat this until it just quits and doesn't surge then back off adjustment by 1/8th turn. If it simply quits when you pinch then it is too lean -- open the airbleed screw 1/8th turn counterclockwise and restart. Repeat this until it just surges before quitting.
Good luck!!!
As MinnFlyer stated, the large screw on the left side of the carburetor (left side if you were sitting in the airplane and the engine was upright) is the air-fuel mixture screw. It is mainly used to set the fuel-air mixture for full throttle. A good starting value for this needle is 3-4 turns out (counter clockwise) from full close, that will give you a rich setting and prevent the engine from over-heating.
The screw on top is the idle stop screw and is strictly a mechanical stop -- when you close the throttle (throttle arm is on the oposite side of the carburetor from the large screw.) look down in the carburetor throat to see if it is totally closed or partially opened. You want it to be almost totally closed with just a slight opening crack -- about the width of a hair. You achieve this by adjusting the throttle stop screw.
The 3rd screw is the air bleed screw (in some engines it is also an air-fuel mix screw). It's primary purpose is to adjust the engine idle. Try a starting point about 2 turns out from stop.
Now you should be able to start the engine. Choke the carb by opening the throttle to full, place your finger over the opening and turn the prop counter-clockwise about 3 times. Bring the throttle down to idle stop and then back up a couple of notches. Put a glow starter on the glow plug. Slowly turn the prop counter-clockwise until it gets hard to turn. Flip the prop counter clockwise -- it should start after 1 or 2 flips.
If after several attempts you get no indication the engine is trying to start check the status of your glow plug -- replace if you cannot get a glow from it outside of the engine.
If the engine starts you should be able to slowly advance the throttle to full. It should now be blubbery rich and ready for adjustment. Slowly close the large screw clockwise a few clicks at a time. Listen for the rpm, after each adjustment it should get faster and faster -- stop when it starts to decrease instead of increase, then back off a few clicks. If you have a tach adjust to about 400rpm below max. This is the way you should always fly the engine -- the extra 400 rpm is usually made back up when the airplane is in the air and if you didn't have it on the ground it would lean out on you in the air -- stall and possible engine damage.
Now bring the throttle down to idle. Pinch the fuel line to the carb until the engine quits. If it surges just before it quits it is too rich -- close the airbleed screw 1/8th turn clockwise and restart. Repeat this until it just quits and doesn't surge then back off adjustment by 1/8th turn. If it simply quits when you pinch then it is too lean -- open the airbleed screw 1/8th turn counterclockwise and restart. Repeat this until it just surges before quitting.
Good luck!!!
