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Super Tigre 90 Quits When Inverted?


craig procter
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22 minutes ago, Ron Gray said:

I may have not interpreted previous posts correctly but have you tried bench running it inverted (with the tank rotated of course!) using your ‘crude’ mounting system?

I haven't yet to be honest, the only thing I done was I removed it from the vice and turned the whole thing upside down whilst it was running, seem to go quite well until I moved the throttle to idle and then it cut...

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It seems ST engines are difficult to tune. One club member had one which gave no clue we were edging close to the correct setting until we finally found it. We could blame it on the rather quirky carbs they use but the strange thing was, they worked perfectly well on early Laser engines.

I have heard that ST engines tend to have rather small transfer ports which contributes to tuning problems.

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10 hours ago, craig procter said:

 I have been using different types of fuel one of them being Opti Fuel 20% nitro and 18% oil.

 

No! No! No! Do NOT run it on high nitro fuel! They were designed to run on STRAIGHT fuel (no nitro at all)!

 

Unless you have some serious shims under the head, it will run like a dog and be difficult to tune!

 

I run all my STs (and my old Webras) on straight, and they run like sewing machines on it.

 

A good way to set the carb up is 1) aim the inlet nipple at the front mounting bolt. 2) open the main needle quite wide, then close the carb to the point where it just traps a pin. Then attach a length of fuel tubing to the inlet and blow. Adjust the idle needle until you can JUST hear the faint hiss of air getting through. 3) put the main needle back to a slightly rich running setting.

 

Setting it up this way will get you very close to a good running setting, and you should only have to do fine tuning to get it spot on.

 

I cannot emphasise enough how - unless you put some thick shims under the head - an ST will never run properly with high nitro fuel! They don't need it, don't like it, and it costs you money! Don't do it!

 

--

Pete

 

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6 hours ago, Andy Stephenson said:

It seems ST engines are difficult to tune. One club member had one which gave no clue we were edging close to the correct setting until we finally found it. We could blame it on the rather quirky carbs they use but the strange thing was, they worked perfectly well on early Laser engines.

I have heard that ST engines tend to have rather small transfer ports which contributes to tuning problems.

I must admit I have not had trouble quite like this with any other glow engine!

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1 hour ago, Peter Christy said:

No! No! No! Do NOT run it on high nitro fuel! They were designed to run on STRAIGHT fuel (no nitro at all)!

 

Unless you have some serious shims under the head, it will run like a dog and be difficult to tune!

 

I run all my STs (and my old Webras) on straight, and they run like sewing machines on it.

 

A good way to set the carb up is 1) aim the inlet nipple at the front mounting bolt. 2) open the main needle quite wide, then close the carb to the point where it just traps a pin. Then attach a length of fuel tubing to the inlet and blow. Adjust the idle needle until you can JUST hear the faint hiss of air getting through. 3) put the main needle back to a slightly rich running setting.

 

Setting it up this way will get you very close to a good running setting, and you should only have to do fine tuning to get it spot on.

 

I cannot emphasise enough how - unless you put some thick shims under the head - an ST will never run properly with high nitro fuel! They don't need it, don't like it, and it costs you money! Don't do it!

 

--

Pete

 

I hear you Pete lol... I'm used to using high nitro on my helicopter OS motor and my Weston UK Velocity. I thought it could only be a good thing to use that fuel on the Super Tigre as well and give me lots of power hehe. Okay I'll some different glow fuel, think I have some other kicking about the garage. I think I have it close to being setup nice  but I will definitely take note of how you told me to set it up, thanks for the info...

Oh, I've seen people saying to point the inlet nipple at the rear mounting bolt???

Edited by craig procter
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24 minutes ago, craig procter said:

Yes they did, okay rich on the high or low needle?

 

If the revs drop it can indicate that the plug is cooling caused by an excess of fuel so lean the low first then re-tune the top. You’re aiming to get it so that the motor transitions from low revs to high without hesitation or stuttering.

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15 minutes ago, Ron Gray said:

If the revs drop it can indicate that the plug is cooling caused by an excess of fuel so lean the low first then re-tune the top. You’re aiming to get it so that the motor transitions from low revs to high without hesitation or stuttering.

Okey dokey I'll have ago, you obviously know your stuff I can tell, thanks Ron...

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42 minutes ago, Ron Gray said:

Lots of people on this forum have a wealth of knowledge far greater than mine Craig so you’ll get a lot of helpful advice, just try them out one at a time!

Yes other people on here have been great too, I appreciate yours and everyone's help on here, I now have a better understanding with what was going on.

It's funny because I can do most things and also have a fair knowledge of mechanics, I work on cars, motorcycles etc all the time so I should have been able to diagnose the problem myself and I've been r/c modelling for quite sometime now but I clearly failed when it came to an inverted engine lol... 

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11 hours ago, craig procter said:

I hear you Pete lol... I'm used to using high nitro on my helicopter OS motor and my Weston UK Velocity. I thought it could only be a good thing to use that fuel on the Super Tigre as well and give me lots of power hehe. Okay I'll some different glow fuel, think I have some other kicking about the garage. I think I have it close to being setup nice  but I will definitely take note of how you told me to set it up, thanks for the info...

Oh, I've seen people saying to point the inlet nipple at the rear mounting bolt???

It depends to some extent on which spraybar your motor is fitted with. The angle of the inlet nipple controls (to some extent) the mid-range mixture. The slit in the spraybar that allows the fuel to flow into the throat of the carburettor should not be facing straight down the throat. Offsetting it slightly improves the pick-up dramatically - especially if you have one of the older spraybars with flats on the sides.

 

The amount of offset isn't super-critical, but the standard setting is point the nipple at the front bolt, and fine-tune if necessary (get the idle and main right first!). I've never found it necessary to fine tune this setting.

 

Nitro will only give you more power if the engine is designed for it. It has a similar effect to advancing the ignition timing on a petrol engine, where if you advance it too far, you actually lose power!

 

Aside from Super-Tigres, I've had a couple of engines that flatly refused to run properly on even small amounts of nitro! One was an AirSupply 40 (Japanese helicopter engine) and the other was a Chinese .36 heli engine. Both ran very hot and spitty - even on 16% nitro - in choppers, and wouldn't tick over properly. After a lot of cursing and swearing, I tried them on straight and after some fiddling with the mixtures, they both ran like turbines!

 

If you must run high nitro, then shims under the head to reduce the compression ratio will help. But unburnt nitro can turn to nitric acid in the crankcase, to the detriment of bearings, and adds cost to the fuel. Avoid it unless you need it. Your OS heli engines (and probably Weston) are designed for it and need it. The ST isn't and doesn't!

 

Nitro is NOT a universal power boost, and can be quite detrimental if the engine is not designed for it!

 

--

Pete

 

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I completely agree with Peter's post

 

its no secret that i am not a fan of huge amounts of nitro. I have found that 5% is normally perfectly adequate for all 2 and 4 stroke engines but there are a few exceptions. YS engines are designed for high nitro, as are many racing type engines for cars, boats and planes. However, many European manufactured engines like Super Tigre, MVVS and Moki recommend either very low or no nitro. At Laser we used to recommend straight and only changed to 5% as there are some small advantages vs straight such as cold starting in winter and slightly reduced needle sensitivity. 

 

Nitro is often touted as the golden bullet for all engine problems and it simply is not true. When you run high nitro you naturally run a richer mixture (in terms of needle turns) as the nitro releases oxygen when you burn it. With more turns on the needle you get more fuel inside the engine and this cools the engine from within. This is handy in a helicopter, but not so much when you are struggling to keep the plug alight. With lower nitro and lower oil (15% not 20%) you reduce the amount of gloop the engine has to deal with and you are far less likely to drown the plug. 

 

Finally though, the root cause is likely as much to do with tuning as anything else and in my experience ST carbs tend to run leaner (number of turns) than most others. I recommend you get the top end peaked and then just keep leaning off the slow run until it will no longer throttle up from idle

 

 

 

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