Super Tigre G30

[Chris Walby]

I recently obtained a L4 Cub with a ST G30 installed, but not run for a couple of years. Being a 4 stroke man as I blame my youth and small but expensive collection of Bultaco racing pistons with holes through the top! there seemed to be a black art reasoning behind it all.

 

Anyway the model came with just over a gallon of Southern Modelcraft glow fuel (no nitro) and no instructions so once filled up and the onboard battery charged it was off to the field. After a bit of tinkering the engine sprung to life and warmed up nicely with a lack of castor smell (not as much as I was expecting so perhaps its a mostly synthetic blend).

 

Tuning and operating advice please? What's normally said "Assume nothing!"

• Clearly start engine with onboard glow switched on and run until cylinder head has some heat
• Switch on board glow off and run at various rpm until engine is nicely warm/hot
• WOT and set for max rpm
• Check engine picks up from idle to WOT cleanly
• Switch on board glow back on (it auto switches off above 1/4 to 1/2 throttle anyway)

 

I noticed a couple of things which might be due to firstly not switching the on board glow back on, just a feature of the ST G30 or the need for further adjustments.

• If I set WOT for max rpm its pick up is not clean when I snap the throttle open, but if I tweak the needle I get that but it won't rev out 
• The engine note has a real crack/pop once I switch the glow off, normal?
• If I hold it as constant revs (anywhere between tick over and WOT) it will every so often do a very slight hick, the rpm does not change. Its just my 4 strokes don't do it, but I seem to remember lots of 2 strokes (strimmer's etc) tend to do it. Any concern?

 

I would like to fly the model with the G30 for a bit, but if its going to be unreliable/need a load of work then I will progress to plan B (4 stroke) which is the long term plan anyway. ?

 

 

[Frank Skilbeck]

Chris, we've run the 25cc version, sounds like for your pick up problem it's "underfueled" i.e. lean when you snap the throttle open, you could try richening the bottom end a little and see if that helps, the other thing I do is put a slight slow on the throttle channel, so it opens up more smoothly (on my Tx throttle slow only applies on opening the throttle).

 

Normal Southern Model craft fuel is generally synthetic with a couple % castor (but they also do a full synthetic mix too).

 

The big Supertigres were OK on reduced oil and you used to be able to by specific Supertigre fuel which was i believe 10% oil.

 

Edit - here it is https://www.jperkins.com/products/5515370

Edited April 16, 2022 by Frank Skilbeck

[jeff2wings]

IIRC the the carburettors on the big ST's all had an issue with low/midrange transition that was only fixed with the introduction of a new carb on the ST 3250 and 2300 engines ,I think one of the fixes back in the day was to use  a OS 70/90 fs carb,I have a OPS 61 carb on my 2500,and the fuel recommended was called big brute .

[Alan Gorham_]

The fix was to use an OS 7D carb as used on the 90FSR or 1.08FSR. However they are rare and expensive these days.

[Geoff S]

14 hours ago, Chris Walby said:

I recently obtained a L4 Cub with a ST G30 installed, but not run for a couple of years. Being a 4 stroke man as I blame my youth and small but expensive collection of Bultaco racing pistons with holes through the top! there seemed to be a black art reasoning behind it all.

 

Compression reducing pistons aren't exclusive to 2 strokes (though the only Bultaco I owned was an old trials bike).  I had the same problem with my 1953 BB34 500cc BSA Gold Star (a very rare model, I wish I still had it) and I still have one of the holy pistons to prove it.  The cure was to replace the aged Amal TT carb with an Amal Monobloc.  It seems, from the other replies, carburettor replacement is the answer in both cases ?

[Engine Doctor]

Your carburation problems are likely caused by using normal fuel ,ie 20% oil. Big Super Tigers or any large glow engine will benefit from a lower oil content. 

Super Tiger specified 10% oil with no nitro. It was called " Big Brute" .  It works well and will transform your engine. Nothing wrong with the ST carb if uts set up correctly.  The fuel slit in the bottom of the spray bar should be pointing straight down. This is indicated by the fuel nopple pointing towards the front left hand mounting bolt hole.

 

Southern Model craft will mix it for you but you will have to collect from his home in Tonbridge or at a show. You can give Alan at Weston UK a call he will mix some for you and can deliver if you order 4 gallons .

The 10% oil allows for more methanol into the cylinder and with the larger volumes of fuel these engines use the 10% oil is more than enough for lubrication.

The "hick you mention at WOT sounds like rich mixture. Check mixture is ok at wide open throttle and at idle. Allow engine ,once warm to idle for 10 seconds. Now open throttle smartly , don't snap it open. If engine coughs and splutters and gradually picks up speed with smokey exhaust, it's running rich and likely is the fuel mix.

This is caused by excess fuel collecting in the bottom of the crank case and being thrown up into the cylinder when the throttle is opened. Reduce idle mix 1/4  turn. And repeat. If opening throttle smartly causes engine to hunt and die with little or no smoke thren its running lean. Find the sweet spot that will allow extended idle with clean pick up then leave it.

Only change carb if you present one is knackered.

[Chris Walby]

Thanks ED and others for your posts and info. I really don't like fiddling just for the sake of it so I'll take the advice on board and make adjustments with probably a tweak of the bottom end as its a bit lean at the bottom end.

 

Some engines don't mind snapping the throttle open and others smartly is the way to go. As the engine is in a Cub its only going to be pottering about.

 

Thought I asked, but do you do all the tuning with or without the onboard glow switched on or off

[Gunnar Borseth]

Hello,

and greetings from Norway. 
 

In my experience the needles on the ST carb interacts a lot more than on other carbs. So you may have to make several adjustments to both needles to find the sweet spot. Once set they are great carbs. 
 

Adjust with onboard glow switced off. 

[Engine Doctor]

Try to get the best results with a warm engine but without the OG switched on.  Once happy certainly use the OG set to switch on below 1/4 throttle to give a very reliable idle .

You may have to make a few attempts with adjustments getting very small for best results.

The big Super Tigers also take a lot of running in unlike modern ABC  engines so ensure that engine will hold WOT for extended period without showing signs if overheating.

[Peter Christy]

Do you have a picture of the throttle? On the smaller STs (up to 12 or 15cc) you could adjust the mid-range mixture by rotating the inlet assembly. This is held in place by two screws.

 

On the smaller engines, the advice was to have the inlet nipple pointing at the front mounting bolt hole. This makes quite a big difference to the pick up from idle on these motors. I'm not sure how this would translate on the bigger engines, a picture of the inlet side would help.

 

You probably aren't using nitro in an engine that size anyway, but STs do not like nitro, and run far better on straight fuel.

 

Once set up properly, ST carbs are as good as you will get, but there is a bit of an art to getting them "just right".

 

--

Pete