vease

Strange thing happening with my sachs 72cc.

No problems with it all when it was put away for winter. Got it out a couple of weeks ago and the engine was a little lumpy to start with but seemed to clear so flew it. It performed fine for a couple of minutes but landed to change some radio settings as I'd installed new elevator servo's. I didn't stop the engine while I was adjusting. Went to take off again and as I got to full throttle it died. Throttled back and it ran fine. I then couldn't get it above half throttle without it dyeing.

I checked the ignition batt through the ignition charge socket and it was very low. Took the batt out and it read higher but was still low. So problem solved I thought, and got a new battery.

Yesterday I tried it again. Same start, ran fine right through the range so took. Flew for about 4-5 mins then as I opened up after a loop it back fired once then the power dropped off a bit but was still reaching full throttle so continued the flight for another couple of mins. Then as I slowed up for landing it suddenly lost all power and died. Thankfully got it down OK. Started it straight up again and couldn't get over half throttle again.

So check the new batt through the ign charge socket it showed 4.4v (its a 4 cell pack), so assumed the new pack was faulty. Took the pack out and checked it direct and it was 5.2v so the batt was actually OK.

I'm getting very different readings direct and through the charge socket. So, could it just be the switch thats at fault or is it more likely to be the ignition unit itself.

I have changed the switch now which I'll try at the weekend and do have another ignition module to try but I just wandered if the scenario that's happening sounded familiar to anyone?

tomfiorentino

Vease,

I would rule out your battery issue since you are on it....but this almost sound like a dirt issue. I would check the in-line fuel filters for crap as it sounds like an obstruction that effects the higher fuel flow demand.

My 50cc behaved exactly the same, until I found what looked like the white part of a dandeline or milkweed seed on the screen in the filter. Perhaps something on the diaphram too?.

Please keep me posted....

Tom

vease

The voltage drop through the switch/charge socket is why I'm looking at that part. It also only happened once the engine had been running for a while.

I will check all the filters too.

coralcape

My Feedback: (4)

Simple to check if there is a voltage drop in the switch. Place a voltmeter across the input and output of the switch. If there is a drop you will get a reading. If no reading, no drop. Good luck, red

vease

yep, thats what I tried to explain. I do have a drop which is why I'm changing it. Would that cause whats happening though.

pe reivers

A faulty switch will be even worse under engine vibration conditions. Also carefully load check all plugs and wiring. Those mini uni connectors are near worthless in conducting any current..

vease

Whatever has happened, its happened whilst not being used. It last flew in October last year and didn't miss a beat. I'll be checking everything I can this week then try it again on Sunday.

karolh

A backfire usually points to fault somewhere in the ignition circuitry, so as Pe suggested give it all thorough check.

Karol

coralcape

My Feedback: (4)

It amazes me that we don't have a lot more trouble with the switches we use. I've taken some apart, and they are a simple slide contact. Your problem is probably caused by setting idle, and the contacts corroded slightly. Can you say WD-40. Good luck, red

thepamster

Wd-40 is good for stopping squeeking door hinges and not much else. DO NOT spray that on a receiver switch. If your receiver switch contacts are corroded, replace it.
I have seen a lot of people trying to fix things with wd40 in the electronic service industry for years. It creates more problems than it solves.

The Pamster
AMa 202345

speedracerntrixie

My Feedback: (29)

Agreed, I would not use WD40 for this but I did have an old '70 Nova that required a squirt of WD40 to dry out the distributor whenever I drove through a puddle. Back to the airplane. I agree that the connectors are corroded. Make sure they are of the gold plated type. If they are gold plated pins, usually pulling them apart and plugging back in a few times cleans them up.

coralcape

My Feedback: (4)

I still swear by WD-40, but with a caveat. My procedure is to spray the part, operate it several times and then wipe off excess. Did that in telecommunication industry for 43 years and retirement for 16. You just can't beat that fish oil ; why it's even good for your heart ) Keep smiling, it confuses 'em, red

speedracerntrixie

My Feedback: (29)

I was not knocking WD40 as an electrical parts contact, it's just that with extensions and switches coming from god knows where, I would not trust that type of solvents we can expose the plastic to. I think everyone should have a can of WD40 around the house LOL.

CK1

My Feedback: (60)

Going by the voltage drop that you have described- I would replace the switch if it were mine . I would not fool with cleaning it, a switch is 30.00 or less and I am sure your plane is worth more than that ......

vease

After testing the electrics at various points it proved that the switch/charge socket does drop the voltage by quite a bit. However I also new that I had flown the model a lot of times and not really worried about how charged the ign battery was...as long as it had some charge it never missed a beat.

Vibration could obviously be a factor bringing down the voltage more or even having intermittent power so the problem was still potentially the switch.

As Tom says though, the problem really does sound like a feed problem. In fact it is reacting exactly as a vehicle my dad owned did a few years ago. It would run fine for a while then choke up and die. Leave it a while and it would be OK again before choking up again.We eventually found that a feed nipple wasn't just a nipple but in fact a long filtered nipple that had what can only be described as a silicon worm inside!!

So, with that in mind the carb on my engine was stripped last night and bingo. The feed filter was cover in a layer of black something! The carb has not been apart before and the model has been flying regularly for over 2 years. The lay up over winter probably allowed the muck to harden forming a major blockage. Result! So, now that I'm 90% sure that is the problem I have left the switch as it looks in good condition but have changed the charge socket for a more standard one.

The onther findings in the 2 flights this year were that at the start of the flights the performance was noticeably better than its ever been! This now leads me to think that the blockage was leaning out the mixture. So, now that I've cleared the blockage I can turn in the top needle and give me more power for the whole flight. The engine was brand new in the model and has done approaching 100 flights so I guess its just starting to run in

Oh and this is the model

pe reivers

So you are not going to replace those ailing electrical connections?

vease

Initially, no. I want to see if the problem was JUST the muck first. However hoping and assuming that it was just the muck, I will then be changing those connectors too........ and putting extra filters in the system

Cheers

apalsson

My Feedback: (1)

Personally, I would replace the switch as well as servicing the carburettor (cleaning the screen, check membranes, etc)
These are routine maintenance tasks that only cost you a fraction of the value of the plane.

vease

I will be changing all those components but not till I've seen if my problems were just the muck. Changing the components will hopefully then just be preventative not cure

captinjohn

Another test would be to just remove the switch and plug in direct. Run the engine andfly the airplane a few times too see what happens then. Silicone spray is good for switches. It prevents further corrsion also. Capt,n

bcchi

You no the switch is bad,change it before you fly.Or go ahead and fly and maybe have a engine out in a bad place.Seems like a no brainer to me.The gunk was probably the main problem. A switch causing a voltage drop is not good.Put in a new one.
BCCHI

tomfiorentino

+1 to plug in direct, and I would ditch the switch altogether.

On my 50cc, and anything I'll build like that in the future...no traditional switches period. A direct plug in with a powersafe receiver (JR name but I think there are others) and a soft switch is a bullet proof way to deliver power to the whole system. I'm surprised I dont hear more guys using them. That, combined with the A123 chemistry, I don't even bother with charge ports cut into the fuse. Fly 5 times and if you don't go home after 5 flights anyway, pull the canopy, safety check connections, pushrods, pull-pull, servos, charge A123's and fly 5 more times....done. I use a volt magic too just to keep an eye on voltage along the way as the led lights are visibly through the canopy.

Anyway, glad to see you found your problem...but please ditch the switch! Beautiful bird!

Have fun,

Tom