Surging engine
 

While I was flying, my engine (Magnum XLS .46) suddenly surged to full throttle or so and then back to normal. It did it several times. Why does this happen?

oops

because you say it went back to "normal" it sounds to me that your throttle servo is going bad, I have had a servo do that, also, check your Arm on the Carb, see if it's loose, see if your Carb is loose, if it is loose push down on it and tighten it up...

or, it could have been that your RX was not receiving the signal well while in flight ???

Jim

K thanks I'll see. I wondered if maybe it came from my engine needles not being adjusted right or something.

Is there a way to tell if the servo is shot? Cause it's been working fine when it's on the ground and we're watching it...

I would try by loading the servo a bit with my finger, work the servo with the stick a bit/more than a few times, see if the servo holds up.

check your linkage, make sure it's not loose.

what type of radio do you have, a real cheap radio will have a weak transmitter and could give you trouble in areas with a lot of waves in the air, I don't know what else to tell you. maybe find a club near you and ask some one to take a look

Jim

I have a tactic ttx 600 with a tr625 twin antenna receiver that I haven't had stress with yet... Are those considered a cheap controller brand?

well, in the wold of RC Planes, it's a $100 setup you can buy for $80 new, so yes it's a bit cheap, sorry for that !!

but I looked them up on-line and I saw something, are you using the "4-Cell “AA” Battery Holder" with Duracell batteries or Everready batteries, if so THAT could be your problem, we do not trust these type batteries in the RC plane hobby, you should be using rechargeable batteries and you should charge them every 2 or 3 flights

Jim

Yes I'm using rechargeable batteries... I'm not sure what brand

edited, for both the Receiver and Transmitter ??

Jim

I have regular AA Duracell Batteries in my tx and 4 hydrimax ultra 2000 rechargeable batteries in the receiver.

On my Rx I only have foam pads underneath not all the way around. Is that a problem?

I usually am the only one flying at a private field so... And also as far as dependably giving signal i use it on my flight sim and it's never had any issuues. I don't know if that's a good way to tell or not though...

well only if you do not know how much power is in the batteries

no problem as long as nothing is touching the RX

well you can not tell how far the signal can travel inside the house

Jim

Yeah I walked away from the plane with the transmitter and kept moving the ailerons and elevator with my friend watching them and I went way farther the I'll ever fly so I think the range is good. Thank you very much for all your help. I really appreciate it. I am sort of new at it.

As you can tell it can be a wide variety of things, so start by trying to rule things out.
1. It's not the needle adjustments. It would either run poorly pretty consistently at one throttle setting, cough and sputter when you advanced the throttle, or stop dead. Ditto for the fuel system.
2. It may be that the receiver is going into failsafe, and it is incorrectly set. Pretty unlikely if you still had control of all the other functions, but read up on it for your system and double check how to set it. Typically it should go to idle when failsafe happens, but yours may be set backwards. You could stake it to the ground while running at part throttle, and see what happens when you turn the TX off.
3. If the batteries are clipped into a battery holder, they may be momentarily losing contact. Best would be to swap for a pack that is all one piece (batteries actually welded together). But check all the connections to make sure they are strong. Wrap the pack (any kind) in lots of foam rubber. Install so that it is in firm, but not strapped tight - the foam needs give to be able to reduce engine vibrations. Ditto on the receiver. Use real hobby store foam rubber. At least 1/4" thick all around. 1/2" is even better. If it is a battery problem, you would be losing all the other controls too. But test to eliminate it as a possibility.
4. Try a new switch, or for a couple of test flights, skip the switch and plug the battery directly into the receiver. May not be practical if it is a pain to get at them. Ditto on all the other controls going out if it is a switch problem, but if you can test it would eliminate one more possibility.
5. While your system is "affordable", it's not a bad system, so again unlikely to be the problem, unless everything else is tried.
6. Do a range check - how to should be in the radio instructions. Do it with both engine off, and then when running. Distance where you begin to loose control should be about the same.
7. Look closely at where the throttle plugs into the receiver - is it tight, undamaged, with no damaged wires?
8. Make sure the servo is not somehow partially coming loose.
9. As the Wasp noted, make sure the pushrod connections at both ends are solid.
10. Unlikely to be the carb, but do as the Wasp said, and make sure it is seated well. Go over all the engine bolts checking for looseness (but don't crank them down super duper tight!)
11. Make sure the engine is mounted solidly - no wiggle at all.

If after all the above seems to pass, I'd blame the servo...throttle doesn't need anything high end, cheap is fine. Going through the above first also gives you a check on the rest of the system, to verify you aren't seeing any quirks there.

K I'll do that but I did notice the carb was a bit lose, it wiggled when I would put the throttle up and down. I could see it looking at the end of the highspeed needle(mines on the end of my carb). Could that have caused it? I just tightened up the screws underneath.

I can offer some information that may be helpful. Then on the other had it may not be related or the cause of your problem.

From 1965 through 1977 I flew control line models. I often had engine surging problems. Now here is the clue. The surging only happened when the fuel tank was almost empty

I don't know . My tank was nearly full.

I did notice the carb was a bit lose, it wiggled when I would put the throttle up and down. I could see it looking at the end of the highspeed needle(mines on the end of my carb). Could that have caused it? I just tightened up the screws underneath.

Yes. IMO. Any variation in the fuel supply can be detected by an audible change in the engine

Almost a guarantee that you found the issue.

K thanks for the help.

the carb is noted for stripped threads, you'll probably need to retap the holes.