poor running sc 46

[Codename-John]

afternoon folks, as the title suggests my sc 46 keeps dying after a few minutes running, its only about 10 hours old max, bought brand new about sept last year.

on the ground it runs sweet, tunes fairly easily most of the time tho sometimes does falter when opening up the throttle from tickover, my clubmates have spent quite a while trying to set the needles but it seems to change its-self somehow, the last time i flew it first flight was great, nearly 20 mins without a problem, second flight ran for 5 mins then died, on landing there was air in the fuel line, started again and had another 10 mins problem free, 3rd flight 5 mins died, landed started again took off then weirdly it runs ok during straight and level flight but during turns starts spluttering, then died.

called it a day there and went home with advice from clubmates to check tank, fuel lines, clunk etc which ive done, checked tank and lines under water all fine, clunk is free away from edge of tank etc so its not a problem with tank.

ive taken the carb off to check it over for debris, worn o ring, loose screws etc and all looks good

one thing i have noticed is that is no gasket fitted between the backplate and the engine case and was wondering if this is correct, or without it maybe its expanding when its heating up and letting air in, hence the air in the fuel line, and general sickness ?

any advice welcomed, cheers, neil

[Phil May]

I have an SC 61 and I had intermittent running faults and this was traced to a worn 'O' ring on the main needle vale. Don't think this should happen though on yours with such few hours, but just a thought

B.P

[Gaz Elliott]

Does the clunk have a filter?? Is it full of debris??

 

Could it be the glow plug needing a little hotter plug??

 

So many varibles. i am no expert though.

[Alan Cantwell]

is it a rear carb version? that has a piece of tubing to the carb up front? had similar, and it turned out it was this bit of tube, he had renewed it, and the bore was too big, it was letting air in, as for the backplate, remove the thing, traces round the boss, onto bit of brown envelope, cut out the circle, place it on the backplate, coat the paper in oil, bolt it up as normal, and trim round with a balsa knife,

[i12fly]

If it is a rear needle, these seem to be susceptable to sucking air into the interconnecting tube/joints, probably as the the restriction of the needle makes the 'negative pressure' in this tube stronger. Tiny splits in this tube can be difficult to spot particularly close to the nipples. I had a similar problem, swapped it to front needle (remove the hex plug at the carb & fit the needle housing from the rear) and problem was solved. The only downside is that it brings fingers close to the prop, but that's another post......

[Codename-John]

thanks for replys, o rings in carb look ok, clubmates checked all through it, took needle out blew down it etc, took feed nipple off to check there all fine, clunk doesnt have a filter, its filtered when being pumped in, plug is an enya no 3, tried 2 different ones, its the front carb version, (so i can trim my finger nails while tuning it, who says men cant multi task ! lol)

ill cut the first few mm off the nipple ends of tubing and try the brown envelope, for next time and let ya know, many thanks

neil

[i12fly]

I once had an SC 40 that was 'bottom tolerance' on the carb barrel, and prone to deadstick if it dried out. A couple of drops of after-run oil on the barrel every month cured it completely, but you did after remember to do it.... Don't know if it helps.

[Bob Cotsford]

My SC52 needs a length of silicon tube over the needle thimble to seal it to the spraybar in order to run reliably, even though the o-rings look ok.

[ZigZag]

Had a similar problem with my rear needle SC40. It was a tiny split in the fuel line to the needle valve letting air in but almost impossible to detect when ground running the motor. May be worth double checking fuel lines.

[Steve Hargreaves - Moderator]

Might it be a or hole in the clunk tube? The one inside the tank.....as the fuel level drops it exposes the split & draws in air.

 

Possible vent blockage causing a partial vacuum?

 

Re-occuring blockage somewhere in the plumbing? We had an SC61 with a rear needle that wouldn't hold a tune......turned out to be a grass seed in the carb, just where the fuel entered the carb.....the seed was floating around causing a lean run as it restricted the fuel flow.....oh yes it took a while to find that one!!!!

[David Mundy]

I had a similar problem with a SC 40, mixture difficult to set and cutting out . After checking tank and fuel lines etc I then found problem was caused by small lumps of rust growing in needle valve seat in carb. Blowing with airline and flushing with fuel will not remove them. To confirm this remove main and idle needles and look through from main needle side. If you can see obstructions you will need to remove them, I used a 1.3 mm drill turned by hand. Since doing this and resetting mixture it runs like new again. I know of a SC 46 that had the same fault and it occurs after a few weeks without use.

[Ed Darter]

Have had similar issues twice before, though not on SC's.

 

First time was because the copper pipe inside the tank had rotted through, the one with the clunk on it. Symptoms were that it was generally ok in level flight but as soon as you pull a loop etc it would die. wouldn't run below 1/2 tank of fuel either. Basically as the fuel level dropped the pipe would suck in air as well as fuel from the clunk.

 

Second time was eventually traced to using a pitts type silencer. This had two outlet pipes on it each with the same diameter a the original silencer fo the motor in question. Checked everything else out (including the above!) to no avail. Blocked one of the silencer outlets and its never missed a beat since. I assume too little back pressure for the engine to run reliably.

 

hth

Ed

[Martin Harris - Moderator]

Best to avoid copper - it's fine for the electric boys but mix in a bit of nitro-methane and copper corrodes rather nastily especially if you're not in the habit of draining the tank after a flying session. Aluminium tubing will last much longer.

[Bored now]

Hi, I seem to be having similar issues with my sc 46. It has run fine since february when I got it new but then a couple of weeks ago it became difficult to start and would constantly cut out.
I removed the rear needle etc and gave everything a check over and clean, I also replaced the short lengh of fuel pipe between the needle and the carb and fitted a new plug.
After re tuning it seemed to run ok again and has had 8 flights all fine, but last night it again became hard to start and when I did get it going it flew ok but I had a dead stick on the second flight. When I started it again it seemed to bog down at around half throttle, also I am pretty sure I could see little air bubbles in the small conecting fuel pipe. Should these be visable or is this my problem? I am starting to lose confidence with this motor but dont really want to swap it as I had it running sweet from new and it worked fine. Any ideas? Esp on the bogging down and wanting to cut out at half throttle?

Edited By Supermarine on 07/06/2011 07:18:17

[YakMad]

Do as Bob suggested and put a small piece of silicone tubing on the main needle, I do this with all my ASP's even from new as the only fault I have with these engines (ASP and SC) is the poor quality 'O' rings on the main and idle needles which wear out quickly. I recently replaced the main needle on an old ASP .61 FS (4 years old) which never gave me any trouble until suddenly it became very unreliable, normal service was resumed once a new main needle valve was installed.

[Bored now]

Yes ok i will try that tonight, is the idea to sleeve the whole shaft? Also where can I get new o rings? I looked on just engines site but could not find any SC spares.
Thanks for your input J

[Martin Harris - Moderator]

Just Engines supply ASP spares - they are, AFAIK, the same engines with different logos and made in the same factory.

[Bored now]

O rite, thank you Martin.

[YakMad]

Just push a short piece of tubing from the needle end up over and past the threads on the needle valve, the idea is to compress the tubing when you screw the valve back in. Just Engines now stock 'O' rings for all the ASP Engines which as Martin says are the same as SC.

[Bored now]

Have tried the tubing this afternoon and it seemed to improve things a bit but its still not rite. I then removed the engine from the airframe and installed an irvine53. The irvine fired up first touch of the starter button so the tank and pipework arnt to blame.

Just got no confidence in the SC now. Maybe its inexperience in setting it up?

[YakMad]

You should a set of buy low and high new needle valves or the 'O' rings to suit as if the tubing improved the performance of the engine then the main needle valve is leaking air, as I said Just Engines stock all the ASP parts which are the same as SC and the parts are fairly cheap. I would not give up on the engine as once they are sorted they run well.

[cymaz]

Thought I would revive this thread. I have the same problem just happening on our Club Trainer.

Excellent running all last year. Now it cuts in the air after 3-4 mins, flying only. I have just put in an entire new tank, plumbing, clunk. I have put tubing around the main needle. It still cut after 3-4 mins in the air only! There is air in the fuel delivery tube. I put a silicone ring from fuel tube off cut around the main needle. Took to the air again...usual cut, usual time. Only this time the fuel delivery tube was full of fuel.

Could this mean the air leak is coming in from elsewhere ?? But why does the engine only cut whilst flying and not on the ground?

I have bought a complete new carb from JE for £22 plus £2 p&p.

Any ideas any one ??

[Former Member]

[This posting has been removed]

[Don Fry]

Leaking round the spigot?

[gangster]

I had an Irvine 61 behave like this once, drove me mad ', tried everything still too many deadstick landings , many in the wrong place. The consequent wear and tear on a lovely Spitfire was disheartening and I vowed to destroy the engine and buy a replacement, (It would have been the first time I let something like this bet me)

With this threat the engine decided to reveal its secret at the 11th hour, I had actually removed the silencer, on the flying field to remove the engine prior to if going in the nearby lake. Cause of problem? pressure nipple almost totally blocked. Engine ran perfectly for years after that.