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Old Dec 20, 2007, 06:51 PM
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Joined Jun 2007
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SC40 engine doesn't stop with closed throttle

I have a new sc40 engine which has been run with a couple of tankfulls to bed it in. However with the throttle fully closed (the hole in the barrel is completely covered plus a bit of extra movement) the engine continues to run slowly and the throttle cut button on the transmitter moves the barrel a tiny bit further and the servo protests audibly but the engine still runs. I have fitted a fuel line clamp to stop the engine but would appreciate any suggestions as to what I might try to stop the engine with the throttle fully closed.

The engine responds well to the throttle with no hiccups or hesitation although as a relative newcomer to the hobby I cannot say that I haven't missed anything. I have only adjusted the main needle since unpacking the engine from the box.
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Old Dec 20, 2007, 07:27 PM
your gonna snap the wings
rctoyflyer's Avatar
covina CA
Joined Aug 2007
210 Posts
maybe an airleak

check that the carb is all the way down and tight to the crank case.is there an o-ring there .i think that if anything else were loose than your engine would probably not run as good as it does.i dont think that your low speed needle has anything to do with it, maybe somebody will know more regarding your question.thats all i can think of.
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Old Dec 21, 2007, 02:00 AM
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turk1's Avatar
Istanbul, Turkey
Joined Aug 2004
847 Posts
Also seal the carb retainer bolt on two ends.
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Old Dec 21, 2007, 04:18 AM
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Joined Jun 2007
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Thanks for the input gents. Both suggestions 'tested' but sadly not the answer.
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Old Dec 21, 2007, 11:14 AM
BAKO
Bako's Avatar
Tbilisi, Georgia
Joined Jul 2004
772 Posts
funny so u wanna tell that there is no airleak? maby your carburator barrel is worn and it leaks air?
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Old Dec 21, 2007, 11:46 AM
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on pipe's Avatar
Omaha Nebraska
Joined Nov 2004
193 Posts
If its not the carb to case, or the backplate leaking air, it has to be too much clearance between the crank and case. There must be a leak somewhere... Ross
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Old Dec 21, 2007, 12:02 PM
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Wayne V's Avatar
London, Ontario, Canada
Joined Jan 2006
1,491 Posts
Well my TT pro.36 has exactly the same problem, changed the o-ring on the needle, checked everywhere else only culprit seemed to be the front bearing leaking, sent it into ACE hobby and they replaced the crankcase, front bearing, pistonand liner. Got it back, fired it up and it did exactly the same thing, even with my finger over the carb pushing as hard as i could it would still run for about 20-30sec. So for my it's still either the front seal or something else in the carb.
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Old Dec 22, 2007, 01:53 PM
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I'm hoping to borrow another similar carb after Christmas which should narrow down the problem. I'll post the result as soon as there is progress.

Thanks for the input and have a good holiday.
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Old Dec 23, 2007, 06:27 AM
NM2K
Ringgold, GA, USA
Joined Jan 2006
1,045 Posts
Quote:
Originally Posted by vintom
I have a new sc40 engine which has been run with a couple of tankfulls to bed it in. However with the throttle fully closed (the hole in the barrel is completely covered plus a bit of extra movement) the engine continues to run slowly and the throttle cut button on the transmitter moves the barrel a tiny bit further and the servo protests audibly but the engine still runs. I have fitted a fuel line clamp to stop the engine but would appreciate any suggestions as to what I might try to stop the engine with the throttle fully closed.

The engine responds well to the throttle with no hiccups or hesitation although as a relative newcomer to the hobby I cannot say that I haven't missed anything. I have only adjusted the main needle since unpacking the engine from the box.

------------


Follow the advice of the other gentlemen. But don't get upset if the engine still keeps running after following the other gentlemen's advice. Sometimes the way the engine is made will prevent it from being stopped by just closing the throttle. It doesn't happen often, but it does happen occasionally. Good luck.


Ed Cregger
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Old Dec 23, 2007, 11:11 AM
Canadian Bacon
flypaper 2's Avatar
Kingston, Canada
Joined Jun 2004
13,176 Posts
One method I use on an ugly engine is to put a piece of plastic pipe over the carb intake,snug fit. Put the piston up till it just closes the ex. port. If it's an airbleed carb, stick your finger over the hole.. Take a can big enough for the motor,maybe cut an empty fuel jug, and fill it just over the motor with gas, kerosen, fuel oil, etc. Blow in the carb and it will show where the air leak or leaks is. Takes a bit of time but it's proof positive. One of the methods I used when I ran a small motor shop.

Gord.
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Old Dec 23, 2007, 03:36 PM
Calm winds and CAVU skies
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Lawton, OK
Joined Jan 2004
295 Posts
Sometimes that I've had that happen, running it wide open for a bit then slamming the throttle back with the kill switch already moved would get them to die. Otherwise just stick a gloved finger over the exhaust hole.
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Old Dec 23, 2007, 07:14 PM
RCAPA #299
jg4660's Avatar
Joined Sep 2004
320 Posts
As long as you can get the engine idle to an acceptable RPM i wouldn't worry about it too much. There's a lot of guys that would kill for an engine that wouldn't "quit", it's better than the opposite problem.

JG
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Old Dec 31, 2007, 06:50 PM
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pentaxman's Avatar
Braintree, Essex, UK
Joined Oct 2004
1,315 Posts
I have had the same with my new SC 52.

I have made one adjustment, and that is to unscrew the throttle barrel stop a little more that it was set.

That helped no end, but now with it beginning to bed in properly she will cut nicely on the servo without too many problems.
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Old Jan 02, 2008, 07:15 AM
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London, UK
Joined Aug 2005
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Same problem with my brand new, just broken-in K&B 20 sportster which is running well except for the closed throttle issue. This problem occurs only with only fuel and not with fresh fuel. The mysteries of glow engines...
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Old Jan 03, 2008, 01:29 PM
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pentaxman's Avatar
Braintree, Essex, UK
Joined Oct 2004
1,315 Posts
Mine is being run on fresh fuel so I do not necessarily think that is the cause.
I may fit a new plug to mine since I seem to be suffering one too many cuts in the air but can't stop the thing on the ground at times.
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