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SC 52 2-Stroke keeps cutting out.


Ben Kelly
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The problem i have is the SC 52 that is installed in my Seagull edge 540. It likes to cut out when the fuel tank is about half empty, now originally i noticed the needle valve was leaning itself out and i have fixed that, then i thought it was overheating so i flew it without the cowl and this problem still persists.

I have checked the Clunk in the fuel tank and it is not trapped or restricted in any way.

 I just cant figure out what the problem is.

Any help will be appreciated.

Cheers. 

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Ohh ye i never thought of that, i checked all the fuel line from the tank to the engine, but it never dawned on me that the fuel line inside the tank can get damaged aswell.

Well i'll check that and if its not then you will be hearing from me again haha.

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its a 3 line setup but as the vent tubes are so near the top of the tank I didnt bend them upwards however when I take it apart to replace the fuel line I will bend those up aswell. Would leaving them straight cause a problem with the running of the engine?
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You say it only runs through half a tank when you fill it ,are you sure the tank is filling all the way to the top ?.

Your next step is to fill it and look to see if the tank is full.

If  your  vent pipe is straight then when fuel reaches the vent  its giving you a false reading because the vent is not near top of tank  The fuel doesn't have to reach top of the tank before it starts to flow down the vent hence why you are only getting half tank runs .

putting bends in the tank vent pipes will cure that ,but make sure they don.t touch the side of the tank so as to block them off  guess how  i know about that..!!!

Hope that makes sense

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i have watched as i filled the tank up to the vents as they are near enough the top of the tank to get it more than 3/4 full but the problem is when the fuel level reaches the halfway point on the way back down it just likes to cut out.
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It certainly sounds like a tank plumbing problem to me too. For the vents an old trick is to file a vee into the top of them. Even if the ends of the vents are pressed against the top of the tank then they can still..er...vent OK.

Make sure you clean it throughly before putting the tank back together though....brass filings in yer fuel equals a short engine life!!!! 

Are you using silencer pressure??

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  • 2 weeks later...
looks like it was a problem with the fuel tube inside the tank, I re-plumbed it and have now been able to run the tank with the fuel level lower than the pipes and it runs perfectly. Now all thats left is to test fly it hopefully this weekend. Thanks for all the suggestions and help. Happy flying.
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  • 1 month later...

Hi all.

The first time I tried a ABC motor It was the same old story as Ben, on the ground fine in the air dead stick after dead stick, and I tried all the same things but It turned out that they just need that little bit more running in than the old motors I was used to it is nice to have good advice on hand as often we do not now witch way to turn.

thanks everyone Owen.

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Im having the same problem, with the same engine. Its in an irvine wildcard if anyone could help that would be greatly appreciated, heres the story: Firstly I ran 3-4 tanks through it, took it to the field and flew it around at about half throttle (would splutter if you messed with the throttle setting to much, although I expected this from a new engine) Then the problems began it started to cut in flight, some of the more experienced guys at the club had a look at the needle settings but still it would cut in flight. Then one of the guys had a look at the carb as it was sticking, and solved that problem. Then the high end needle fell out in flight, by this time I was about ready to go all electric. Then the threads on the bolts securing the carb stripped, so I bought a jen carb, they sent me the carb with the non-remote high speed needle. As I didn't want to wait around I fitted that carb and ran the fuel tubing from the tank straight to it. I also replaced the tank as I suspected a leak. With a brand new tank and carb I was sure that I had fixed all of the possible problems, and yet this time I couldn't even get the plane into the air, it would run perfectly on the ground , in the pits, but cut as soon as you added throttle to take off (this had happened a bit before the new tank and carb, but the plane would atleast recover and head skywards) By now I think this thing is scared of heights or something, Sorry for the long post but if anyone had any suggestions that would be hugely appreciated. Thanks Michael
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The suggestions are only going to the same as those for every similar case really Mike. The 2T motors we use are pretty simple things really, with very few moving parts or complicated seals etc - they dont ask much from us and put simplisitically they are

1) clean air and fuel in the carby supplied from a properly positioned vented tank with no leaks anywhere

2) compression in the cylinder

3) a glowing plug element.

People will go on for ever about fuel mixtures and all sorts of other stuff....but if the basic ingredients above are there, it will run. The vast majority of running problems are down to either 1) or 3) and I suggest you get it out of the model. Take off the carb, remove the plug and clean everything thoroughly with clean fresh fuel containing 5 - 10% nitromethane. Throw away all the fuel tubing - even if its new / looks fine etc....throw it away, including the clunk line inside the tank. Fit new tubing, and check that the clunk tube inside the tank is free to clunk around - and be especially careful that it has no pinholes or tears in it from chaffing on the brass / ali pipework and so on. Set up the engine in a test stand, firmly fixed to the bench, and set the tank at the correct height ( centreline of tank roughly in line with the carby spraybar ). Throw away the plug and get a nice shiny new one an OS number 8 or similar ( you could even try a nice OS 4 stroke plug....sometimes they work well in a 2T motor ). Make sure the plug glows nicely when connected to your glowstart cell. Fit the plug with its copper washer to your sparkly clean engine. Fit a balanced prop, screw out the needle valve about 2 turns from shut, and light the fire. Spin her over with an electric starter, and stand back and enjoy the marvels of 2 stroke engines. Tweak the needle to peak it out, then richen it back slightly about a half turn. Now, fit it back in the model and if it doesnt do the same thing then your tank is in the wrong position, and absolutely nothing else could be causing a problem. HTH.

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Going by that it must be the tank position, but the tank is level, if a little high due to the semi inverted engine. The problem is there is no other place for the tank to go it literally just fits in the cavity with no spare space, it ran fine when the previous owner used it ( with a different engine) so my thoughts were that there was something fundamentally wrong with the engine itself. thanks for your help Michael
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Mike, I have this very model powered by an ASP52 (which is basically the same motor as an SC52) & it is one of the most reliable models I have every had....it always comes to the field with me as its guaranteed trouble free flying!!!! That said I'll probably have loads of problems next time out!!!

How is your motor fixed? About 30 degrees off inverted as per the instructions? If so then the tank position is fine & as you point out you can't change it anyway so lets forget that.

You stated in a previous post that the mixture needle fell out......it must have been screwed way, way too far out for that to happen (assuming the antivibration clip is in place!!) My feeling is a blockage or split tubing is causing the problem.....are you using a remote needle? The tube between the carb & needle can split or you can get bits of debris in the carb where the needle usually fits. As Timbo says above...replumb the tank...new fuel tube throughout & reset the carb needles (main & idle) to manufacturers settings (post again if you're unsure how to do this...) make sure everything is clean & unblocked, use fresh fuel & a new plug & your problems should disappear. SC motors & J'EN carbs are good dependable units....obviously there will be rogue items but these are very rare... 

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Thanks for all your help guys. Yes the engine is installed about 30 degrees off inverted so that the exhaust goes down the center line of the fuzz. I am not using the remote needle as the carb that jen sent me had both needles up front, so I just bypassed the old remote needle mount and went straight to the carb with the clunk line. I will replumb the tank, have a good look at the carb and clean everything out. What are the manufacturers settings for this engine? i.e how many turns on each needle. Yeah everyone at my club has great luck with the sc's so its just me thats been having problems I am using a three line system, when i changed to a new tank I was going to only use two line , as I love the simplicity, but I found that the bung had all three holes punched out already. The third line it hanging out through the firewall blocked with one of those fuel line pincher clip thingys. The club member who owned this plane before has kindly donated the engine that he used in it, so that I can see if its the engine or tank set up, I will try this if I have no luck with your suggestions. I am off to the states tomorrow so I will not get a chance to test it out for atleast two weeks. I will however post up the results when I have them. Thanks Michael
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