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SC 70fs idle trouble

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JC01/06/2011 20:40:23
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Hi guys
 
The only way I can get my new SC 70 to idle is when the idle needle is about 15 turns out. Even with my limited experience this seems a lot. Also when it is running at speed I can open the main needle to my hearts content and it does not start to run rich. When I close it down it does lean out as normal. The main needle seems loose also. Looser than the main needle on my SC 52 fs. I cannot get it to idle correctly. It is either too fast or it dies shortly after the glow starter is removed. I have set up both 2 and 4 stroke engines and they run well. This has me beaten. Any ideas?
 
Thanks
Jon
Former Member01/06/2011 20:54:25
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[This posting has been removed]

Martin Harris01/06/2011 21:03:22
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I'm wondering if there's a restriction in your fuel supply - foreign object, kinked pipe, blocked breather perhaps?
 
That may explain why you have to have it set at what should be grossly rich to idle and transition (would explain it's readiness to cut when you remove the glow lead) and why the main needle is ineffective at wide open settings. It should cut the revs dramatically when you open it more than a couple of turns.
Myron Beaumont01/06/2011 21:15:50
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Martin
Totally agree -it's a plumbing prob . Too much air or too little fuel flow ,
Tom
In the case you mention,could it not have been a bad valve seating/closing problem remedied by using up a lot of fuel and depositing carbon etc on the valve/seat interface ? 2 stroke fuel containing more oil would help the "bedding-in"
JC01/06/2011 23:02:16
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The plumbing seems fine. The lines are short and kink free. I will strip out the tank and check the bung, lines, pick up tube and clunk. Thanks for the advice fellas. I had not thought of a fuel supply problem. De fueling did seem to be harder work than normal.
 
JC
Former Member01/06/2011 23:25:58
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[This posting has been removed]

Alan Cantwell01/06/2011 23:31:22
3039 forum posts
remove the nipple from the carb inlet, check the hole, i sorted one like this for a mate last year, the hole was not drilled all the way through, simple as that, if its new, send it back!!!!!
Richard Harris02/06/2011 00:02:43
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Jon,
I have had the same problem with the same engine, though it was well used. Turned out to be a broken valve adjuster ! runs like new again.
 
JC02/06/2011 16:49:52
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Thanks again guys. I checked the fuel lines and found that I had kinked the fuel feed when I installed the tank. I have rectified that but will check the valves and the inlet nipple as a precaution. I'm off up the patch in a moment. I will check back with any news.
 
Jon
JC02/06/2011 19:53:08
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Still no joy. It will only start and run with the idle needle turned a long way out from closed. The valves move freely and the inlet nipple is clear as are the crank case breather nipples. Block the exhaust and it draws fuel freely.
 
Yours stumped
 
I should add that I'm using 10% nitro robbe fuel. Good stuff according to my club mates. 

Edited By JC on 02/06/2011 19:55:34

Martin Harris03/06/2011 00:55:16
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I think I recall hearing about someone whose fuel pipe had a small flap inside or a weak section . Something like this could be acting as a valve - closing under suction but opening under pressure - as could happen when you block the silencer outlet.
 
It might be worth changing the fuel pipes?
Delta Whiskey03/06/2011 17:13:56
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My SC 70 never seems to idle low enough to stop it pulling the model, though one flight this week out of about 6, I managed to taxi out and all was well, 10 mins later, I could not get the tick over slow enough again, despite putting the throttle trim all the way down !
 
Now it could be that the model is just too light or I'm over powering it (Freestyle Sedcution) pic to follow soon......but why was it ok for the one time when nothing's changed ?
Delta Whiskey03/06/2011 17:25:01
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Stefan Hafner03/06/2011 17:28:46
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Have you checked the valve spacing, if the gap is too big it would mean that the valves aren't open long enough, so you would need to have it set rich to get enough fuel to run at all.
 
DW, theres no such thing as an overpowered Seduction , love mine to bits, on the 3rd one now. How long are you waiting before adjusting the needles, as it will warm up and affect the running properties of the engine, hence different at the end. I use a kill switch on my control set to shut the throttle completely, might be an idea if you have the facility
Delta Whiskey03/06/2011 17:44:43
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Thanks I do have a kill switch setup, in fact it's really a must for any IC flyer in my opinion ! I'd just like to be able to taxi it out rather than having to carry it out ....leaving for couple of minutes after starting and it's been warm this week too.....I'll have to fit some brakes to it !

Edited By Delta Whiskey on 03/06/2011 17:46:11

JC03/06/2011 18:20:15
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283 forum posts
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Thanks. I noticed when checking everything that the crankcase breather nipples were both only finger tight. I've nipped them up and will check the engine again. What is the correct clearance for the valves? I have an OS kit with two feeler gauges in it so I must have a read of the instructions. If this does not work I will have to remove the carb and check the idle needle. That means taking the engine off the model.
 
cheers
 
Jon
Alan Cantwell03/06/2011 18:52:25
3039 forum posts
valves should be set at TDC, both shut, clearance should be .025mm, to .1mm one should go under, one shouldnt
JC07/06/2011 13:16:50
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The valve clearances seem ok. It looks like I'm going to have to take it apart.
 
Jon
Delta Whiskey08/06/2011 21:13:29
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Anyone point me to the manual for this engine?
Martin Harris08/06/2011 21:33:25
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This will be pretty close...

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