blw

My Feedback: (3)

That short length of fuel tubing is a source for leaks.

1QwkSport2.5r

I was just looking at that carb today but I have not done the work yet. I will be working on it soon. When I do I'll let you know.

Big or small bubbles can happen from vibration, nucleation is usually tiny tiny bubbles. What kind of clunk are you using?

1QwkSport2.5r

Enlighten me as to how that piece of tubing can be a source for leaks? In all reality it is not gonna cure fuel leaking out of a needle valve but moreso just moving the leak away from the needle some. Fuel tubing or not, air will not be leaking in; only fuel leaking out.

karolh

I still have a non PDP ST.35 and a Blue head .60 with the factory installed PDP, both of which have been updated with Bowman rings and Boca bearings. Both are sweet runners, you just have to be careful with their fairly brittle and easy to break carb needle.

jeffie8696

I installed a blasphemous Thunder Tiger carb on my 40,

1QwkSport2.5r

The ST carb is so much better though... The midrange adjustment is such a nice thing to have.

hsukaria

I also have my ST51 on a Great Planes Escapade. It hauls the mail, as they say. I am using a MACs one-piece muffler to lighten up the nose, there are no noise restraints at my club though,

I did check the fuel tank and tubing. I changed out the metal tubes in the rubber stopper to ones that were slightly larger diameter to ensure a tight fit. I also discovered that there was a small piece of thin tubing under the clunk tubing. It was very thin but I don't know how I missed it. It must have been dark in the basement when I replaced the tank. I also wrapped the tank with foam to reduce vibes. I remember that I had replaced the prop from a Master Airscrew to an APC prop of the same size. The prop is balanced and the plane does not shake.

So if this problem is resolved when I fly it next time, I would blame the extra piece of tubing that was on the clunk under the main clunk tube.

karolh

Back in the day a Perry carb was an excellent replacement for the old style ST carbs especially when the needle valve broke off in it's threaded housing as it usually did during our then frequent unscheduled landings. Are Perry carbs still available ??

1QwkSport2.5r

Perry carbs are still available AFAIK, but they are very sensitive to debris and the plastic bodies are prone to cracking. Personally, I'd buy an ST carb over a Perry any day of the week. The carbs that have the wire needle valves can have the spraybars swapped with the older style spraybar that uses the brass knurled needle valve which is much stronger and more rigid. I think the ST carb is an upgrade over most 2-needle carbs even with a wire type needle valve. If anyone has any Super Tigre carbs they dont want for whatever reason, I'll gladly take them off your hands.

blw

My Feedback: (3)

I meant the fuel tubing from the remote needle valve to the carb.Was I asleep at the switch again?

Evolution engines were shipping with cheap, brittle tubing that would start to suck air pretty soon after heating up.

1QwkSport2.5r

Barry - I think you missed a few pieces of information as to the engine in question. Below is the quote that started the recent discussion about fuel bubbles and leaks.

jeffie8696

When the needle broke on mine and I couldn't get a replacement from Great Planes I swapped it out, it runs great so I lucked out. ST parts are getting hard to locate, I have helped several people get parts with my contacts at Great Planes recently.

blw

My Feedback: (3)

I was just chipping in with a hard learned bit of info to add to things.

hsukaria

I know in the past I did have a bad piece of tubing for the clunk line. That allowed air bubbles to the carb. But this time, it was a new piece of tubing for the clunk line.

1QwkSport2.5r

Duly noted.


I think every new pilot should run their new engines on airboats before airplanes... Good way to learn the idiosynchrocies of stuff like this without losing a plane because of it. Haha. Okay some may not agree, but this worked great getting me in tune with the infamous SuperTigre carb. Good way to learn how hard it is to get rid of those pesky fuel line bubbles sometimes too.

Charley

My Feedback: (2)

What if you live in the desert?

Seriuosly, "infamous ST carbs."? I've only run Sarurno STs but I've found the Mag 3/4 carbs to work fabulously, if you know how to set them up.

CR

hsukaria

Other than making sure that the spraybar slot is lined up directly straight down before starting to tune my ST carb all the other tuning is the same as other regular 2-needle carbs for me. Since I switched to 5% nitro from 15%, I have not needed to adjust the spraybar rotation for throttle mid-range. The reputation of ST carbs being different, tricky, or difficult is exaggerated from my experience.

1QwkSport2.5r

Some people just don't understand the ST carb. The idle mixture is set for just that - a low stable idle. The idle mixture shouldn't be adjusted for leaning or richening the midrange like on typical 2-needle carbs. That's the misconception with them and why so many have problems. I've read numerous forums where guys swapped in OS 7D or ASP 1.08 carbs onto the various ST engines to cure the midrange burble they sometimes have. They just take a little but more time and patience to get them dialed in just perfect.

My S90 needed spraybar adjustments to get a nice transition/midrange until it had about 2-2.5 gallons of runtime. Now I keep the spraybar straight in on that one and it runs pretty good so long as the fuel isn't bubbly. The .29 and .51 I have didn't need any adjustments of the spraybar though I haven't shaved the spraybars down yet.

As as to the airboats in the desert comment - air filters and lots of thrust would do the trick!

aspeed

A plane can glide in, an airboat, you have to bring a boat, go swimming or go through the swamp.

1QwkSport2.5r

I bring a fishing pole. Much easier.

flyingagin

Well the desert is not a hazardous environment for a dead stick (is it called that for air boats?). We got these guys. This is a little guy. I ain't swimming after nothing! It is some what discouraging.!



Ken

hsukaria

Well, I tried running my ST51 with the corrected fuel tubing and wrapping the tank with foam. At first it would start for a while and quit. Then it wouldn't start. I tried a different glow plug, glow starter (with an ammeter), different throttle settings...start. I can see that the engine is not drawing fuel into the carb, like there is no suction. The fuel does come out when I disconnect the tubes from the carb and muffler and blow into the muffler pressure line. That's making me think it is now in the carb or loss of compression?

N1EDM

My Feedback: (2)

Could something have gotten into the fuel nipple and blocked the spraybar somewhere? That happened to me once.

Bob

1QwkSport2.5r

The G51 carb has great fuel draw under normal circumstances. Pull the spraybar out of the carb and pull the needle out of the spraybar and make sure there isn't any crud in there as mentioned in the last post. Not a bad idea to remove the idle needle and make sure that passage is clean as well. I've had it happen to me (finding fuzz in the needle assembly) and now I use fuel filters on almost all fuel tanks (between carb and tank).

The engine ran fine before, I remember you complimenting it quite a bit. Something changed that is making the engine not behave and run correctly.

aspeed

When starting, I usually put my finger over the muffler while cranking it with the starter for about two seconds. This forces fuel through the carb if it is dirty, and ensures that there is fuel in the line when it does fire up. Normally a bit will spit out of the carb. then you take your finger off before it floods. The same effect can be had by putting your finger over the carb but it will flood easier and you can cut your finger easier. Once it is running momentarily you can put your finger over the muffler to force crap through the carb too, or give you time to open the needle if that is what it needs.