SC61 & SC52 engine issues

[Simon Lumsdon 1]

So have a couple of SC engines which are very bad starters and looking for advice please. Have googled all the threads on setting up high speed needle, low speed needle and trick blowing air into carb etc but no success. I have checked o-rings but they seem ok.

First one is an SC61 in an Extra, inverted,12x6 prop, is a sod to get started but once running goes well, it throttles down ok although low speed idling is poor. High speed is fine, leans out nicely and throttles ok but low speed running a struggle. Getting it to start is hard since its enclosed in a cowl, inverted and doesnt draw fuel well when cranking WOT. Have tried the blowing into fuel feed when throttle open (ok) and when closed (blocked), adjusting idle valve doesnt unblock air flow, should it?

Second engine is SC52 and its equally difficult to start, low speed idling is poor as is throttle up. 

Puzzling thing is neither engine seems any good at drawing fuel when WOT? Using a 12v gel battery and control panel flow feed which work fine on various 4 strokes and an fp40 (but they are all OS) Starter isnt the strongest, do i need a geared starter?

Just to be clear, i can get the engines to run eventually and they sort of behave, its initial starting which is the main challenge?

 

All ideas appreciated

 

Many thanks

 

Simon

 

 

[Brian Cooper]

I don't know what "WOT" is but try squirting a bit of fuel into the exhaust/silencer and then rotate the model to make sure the fuel gets onto the piston, and then turn the engine by hand to ensure that the juice has found its way round the engine. . . . And then turn the model again to let any excess fuel back out through the exhaust.  We don't want to have too much fuel left in the engine or there is a risk of hydraulic locking and causing some damage. 

 

Basically, the engine needs to be wet (primed) before it will fire. . . But not flooded. 

[Simon Lumsdon 1]

Sorry WOT wide open throttle

[Denis Watkins]

The trick with Wide Open Throttle Simon, is to have your finger over the carb intake at the same time.

A similar effect is to momentarily block the exhaust outlet while cranking.

There is very little draw with WOT alone.

Your glow plug elements need to look like chrome, and not look a dull grey.

The blow method 1st tune is an excellent method, so revisit that.

Edited May 4, 2022 by Denis Watkins

[Nigel R]

 

 

There is lots of fuel draw at wide open throttle, BUT, only when the engine is going at 10k rpm.

 

I usually do the exhaust outlet trick, and turn the engine by hand 5 or 6 times. That forces some fuel up to the carb. Obviously not with the electric starter though. That carries a big risk of hydro locking the engine and busting the rod.

 

If the engines are hard to start I would recommend making sure the needles are tuned nicely for best operation. Full throttle, nice idle, good transition, etc. From your description it sounds like the needles are not quite there yet. If set right then most engines are somewhat easy to start. Usually they are difficult if one or other needle is not set right.

Edited May 4, 2022 by Nigel R

[Engine Doctor]

For starters , ex pun, don't start or try to prime with  wide open throttle unless turning by hand with finger over carb inlet or exhaust. It's very easy to flood and lock up an engine especially  if mounted inverted and damage internals.  From cold try  as per earlier posts, opening throttle to fast idle position and block exhaust then flick until engine feels wet and free. Then try starting.

If idle is poor then  fue lmix is still wrong and news some fine e tuning. With the 61 an onborad glow that activates at low throttle may help but I would try adjusting idle mix first. 

[extra slim]

engines which seem to run ok once going but are tricky to start for me anyway, tend to need the slow running needle richening up 1/4 turn or so.. Not a fan of SC52 two stroke carbs, you seem to either get a good one or a bad one... Clubmate is struggling with his, and I suspect O ring issues.. 

[Simon Lumsdon 1]

Well i didnt know the trick with blocking exhaust to draw fuel in so will try that. Will also check plugs are good. Agree with comments about these engines being sensitive to idle valve settings. Thanks

[Richard Acland]

How old is the fuel you are using. I had a similar problem. Getting 5 litres of new fuel sorted things out.

[John Wagg]

1 hour ago, Simon Lumsdon 1 said:

Well I didn't know the trick with blocking exhaust to draw fuel in so will try that. Will also check plugs are good. Agree with comments about these engines being sensitive to idle valve settings. Thanks

This only works if there is an exhaust pressure connection to the tank, which I assume you have.

I have 2 SC's like you, a 61 and a 52. The 61 is good at full throttle but only passable at lower throttle. Starts reasonably easy.

The 52 I just can't get to throttle at all. Again starts easy enough but something not right with the carburation. ?

 

 

[Simon Lumsdon 1]

Thanks John, sounds like a similar experience to myself, poor throttling being the main one, point about exhaust pressure makes sense and is going to be very helpful priming a cowled engine. Im also going to buy a Just engines geared starter, current one is too gutless

[SIMON CRAGG]

How old are the engines? Do you know their history? Were they stored with after run applied?.

 

I would be tempted to strip both of them and replace both bearings in each engine.

 

They are not silly money from your local motor factors.

 

I have replaced countless bearings, and nine times out of ten the old items were rusty / dragging to a greater or lesser degree.

 

Hope this helps. Nothing more frustrating than spending ages fiddling with a bad tempered engine, for it to go dead stick just as you take off!.

[Doug Campbell]

I would check the o rings on the needles first. They age and leak air. Quick easy fix to try first

[John Wagg]

59 minutes ago, Doug Campbell said:

I would check the o rings on the needles first. They age and leak air. Quick easy fix to try first

That's a good point. I did put a piece of silicone tube over the needle on the 61.

 

 

[Nigel R]

Worth making sure the front bearing is sealed or shielded - engines can draw air through open races. Which can make for odd throttling and/or difficult idle needle setting.

[Simon Lumsdon 1]

Engines are both in good condition with smooth bearings, o-rings are fine (and i do have spares), think these engines are just very sensitive to idle needle settings. Fuel is also fresh. Think i will stick to OS engines in future

[Gunnar Borseth]

I owned a SC 52 some years ago. The idle needle was very sensitive because it’s blunt/square on the end. After 7 deadsticks in a row I got mad and pulled out the needle, put it in a drill and filed the last 2 mm of the tip sharp. After that the engine ran like a dream. It may be wise to check if spare needles are available before you go this route. 

[Simon Lumsdon 1]

Have noticed the same thing, also tried blowing down fuel pipe trick and carb is blocked when throttle closed, which suggests idle might be blocked, need to investigate that further

[Cuban8]

I have an ASP61FS that exhibits exactly the same starting chracteristics. The engine is old and well used and runs perfectly well and reliably once it gets going, but has very little suction to draw fuel through to start - its been like it for years despite several strips, cleans, valve adjustments etc etc. There is a definate knack to getting it going without wasting too much time and what I've discovered quite simply is that it need to be very wet to get going......wet but not flooded, allow the plug to warm up for a while and to clear the element, and then with a couple of back flicks to check for hyraulic lock, she'll either get going from that or a quick tap from the starter will usually see her away, presumably once a bit of exhaust pressure to the tank builds up.

Getting enough initial fuel into the engine sometimes means removing the main needle and squirting a bit of fuel into the carb (engine within a small and tight cowl) or even a bit down the exhaust and in via the head.

Hope this helps.

 

 

Edited May 6, 2022 by Cuban8

[extra slim]

3 hours ago, Simon Lumsdon 1 said:

Have noticed the same thing, also tried blowing down fuel pipe trick and carb is blocked when throttle closed, which suggests idle might be blocked, need to investigate that further

You need to leave a tiny fraction open (put a pin in) when using the blow down method, or else it will appear blocked if closed all the way

[Jeffrey Cottrell 2]

Hi Guys

Got a similar issue with mine, wonder if I could piggy back on this discussion and get some advice.
So, here's the deal:
Bought a second hand Ripmax Bullet at W & W, which had an SC 52 2str fitted. Had a couple of flights 'as is' enough to prove the model would fly well, then on to the bench for a little tlc.
My issue is trying to get the idle needle set.
On WOT, runs clean and absolutely screams on an 11 x 7 prop, but doesn't like to tick over, and transition is very hit and miss.
Obviously being an aerobatic model, won't be running flat out all the time, so could I get some ideas on how to set the needles for smooth transition?
Seems to me it's too rich at t/o judging by the amount of raw fuel coming out the silencer, but screwing the idle needle in seems to make it even richer.
At the moment, ticks over smoothly for a few seconds then gradually dies, and throttling up then might increase speed, with a lot of popping and banging, but more likely killing the engine altogether.
I have stripped and cleaned the carb, but found nothing odd. Before I did I measured how many turns out on both needles, and reset to that after assembly. However, no way of knowing whether the previous owner had done any tuning, so first of all, could I get some ideas on how to find starting settings for both needles?
Sounds like a good first stage to me.

Thanks

Jeff

 

[Denis Watkins]

In a quiet place Jeff, you can set the low needle with a piece of fuel tube on the carb, long enough to blow down.

Set the barrel on low idle, by hand, about 20-25% open.

Blow down the tube and you may or may not hear the air hissing.

Open the slow jet, turning counter clockwise, to hear a hiss

While blowing, turn the low needle clockwise slowly, - slowly -

Until the hissing just stops

Then open very slowly until the hiss just starts again

 

You are now very close to the correct low end tune

Fuel up and tune the top end for full chat and he amazed you can get back to tickover

Edited July 7, 2022 by Denis Watkins

[Jeffrey Cottrell 2]

Hi Denis

Thanks for that, exactly what I need. Will let you know how I get on.

Cheers

Jeff

[Denis Watkins]

This is a published procedure Jeff, not thought up by me

But it does work

You can listen for the high needle too being correct, hissing when the barrel is fully open.

[Jon H]

The blowing through a pipe method will get you into the ballpark but there will be more you can do with the engine running. Its great if you are totally lost, but it will not give you the perfect setting