Ive got a Hobbico Superstar trainer with a Super Tigre GS-40. I prime it and it starts fine and runs for about 20 sec. and then dies. If i try to restart it it won't start. If i pull off the exhaust hose and blow in the tank it will fire right up again. I pressure tested the tank by blowing in it and pinching both lines then letting go after about 30 seconds and i can hear a puff of air come out so i'm sure it is sealed. I also pulled the exhaust off and cleaned it and made sure everything was clear. Also, when i prime it it will suck fuel up to the carb but it will not stay there. What else could be causing me to lose pressure after running for a while?

have you checked the nipple on the exhuast to make sure its not plugged?

Yes i have, thanks for the suggestion.

Your low speed needle valve may be too lean. If the tank is slightly lower than the carburetor, the fuel will flow back into the tank when the engine is off. This is normal. If the engine is tuned up right, it will start on the prime and then the carburetor will keep the fuel flowing.

But if you are starting at low throttle and the low speed needle is too lean, it will burn off the prime and quit.

Try starting it at one-third throttle or even full throttle. If the HS needle is open 2.5 turns it should start even if the low speed NV is off.

You may simply have the engine to lean to run after it runs out of prime. You may have dirt in the carb inlet which is causing it to go lean. Are you using a fuel filter?, if not , get one. Do you see bubles in your fuel line when running?, if so you have an airleak somewhere. Are your fuel lines reversed. Is this a new engine?, if so are you breaking it in per instructions. Did you try replacing the glow plug?

these may sound dumb but you might check that you don't have the lines crossed, done that one a few times myself and check that your exhaust tube in the tank points up

It is a new engine. I have ran it with the HS needle everywhere from 2 to 4 turns out and it runs best at about 2 1/2 out. I have started it at half throttle and ran it wide open and it will just all at once quit after about 20 sec. even at wide open or any other throttle position. I pulled the carb off and set the low speed needle so then end of the needle is right in the middle of the "cat eye" just like the manufacturer suggested and have even turned it out a couple turns. And i had the tank out last night and i am positive the lines are hooked up right. The vent goes into the tank then curves up to the top.

Given the information in the thread so far, I'd suspect an air leak in the engine (carb inlet, needle valves, maybe even front bearing), a bad glow plug, or bad fuel.

I have seen vent tubes that bend up and are flush with the tank - enough so to make a seal when pressed in hard with the stopper. I either nick mine with a file or pull a lip down with round nose pliers so it always allows air passage.

When your engine dies does it do so suddenly or gradually? Does it speed up slightly first?

check your fuel lines you may have a pin hole in them

Get some local experienced help if you can; these problems are hard to troubleshoot at distance.

You can isolate the problem by running the engine in a test station or by feeding the engine with a provisional second tank located higher than the carburetor (hold it with rubber bands over the fuse), or even by the fuel jug also high.

That way you will know if the problem is in the tank or in the engine.

Whatever you do, please, be very, very careful around that propeller.
They bite frustrated RC pilots easily.

This was on an older plane, han a split in the supply line in the middle of the stopper for the fuel tank. OS 40 would run fine for a while then die, bubbles in the fuel line tipped me off they were easiest to see when I held the nose up with the engine running now I ck this every flight.

Hi!
Open the low speed needle! The low speed needle interacts with the high speed needle. If it is turned in too far ...not enough fuel will pass to the carb.

Super Tigre 40 is one of my favorite engines among all my collection. (The previous italian version)
The unique problem with it, is that it is very misunderstood.
At first flights your low speed needle valve should be somewhat open; this normally will tend to stop the engine from running when you open suddenly the throttle.
You have to live with this issue maintaining the engine a bit open with your TX throttle trim. (Just for a short time)
After one gallon or so you may start leaning the low speed needle valve until the engine transitions from low to high with out any problem, after several more flight this task will have to be done again and from there you will never have to touch the needles again.

I hope this can be of help.

Best regards.

Alfred.