Leaking Super Tigre G90
 

I'm hoping someone can help me with this. I have an old Super Tigre G90 that has a leak around the carb. Can anyone tell me if there is supposed to be some an o-ring or seal of some sort that fits around the HS needle body? The HS needle body was knocked off of the carb body when trying to use a stick to rotate the prop to start the motor. It looks like there should be an o-ring there. If so, does anyone know the size?
Attachment 2227212

Attachment 2227213

This looks like it is missing an o-ring or seal.

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Attachment 2227215

I don't think they had an O-ring there.

No o-ring there from the factory. However there is no need to be one present if the spraybar is intact. I'm 100% positive that carburetor needs a new spraybar assembly. The attached picture shows what the spraybar assembly should look like. Usually the .61, .75, and .90 have a flat spraybar unlike the round one I pictured. The same principle applies.

I think I have a couple of extras, I'll see if I can fix you up

I like an engine that has a carb that is designed from the start not to rely on o-rings that wear our or tear up. Less things to watch out for.

There is more to this story than we are getting here.

You can see that someone has been diddling with that carb. The bolts which retain the spray bar have been chewed up. They don't come that way from the factory. That's the result of a hacker.

In the first pic, you can see where near the top, both the spray bar and the carb body have been mangled. Marks are quite obvious.

In the third pic, you can see the remains of where the long shaft end of the spray bar has been broken off the base. There is a crumpled looking bit sticking up by the needle valve. Fuel will come out there, not in the carb throat as intended.

Super Tigre engines do not use an O-ring between the spray bar and carb body. The fit is quite precise. However, if you are trying to use broken parts and destroy the fit between the spray bar and the carb body, things won't work properly.

Both round and flat spraybars have been used in the various SuperTigre engines. From the pictures, the spraybar is broken and completely useless. With a properly-fitting spraybar installed in the carburetor, fuel cannot leak between the spraybar and carburetor body. If the seating area was not cleaned from both components the last time they were taken apart and reassembled, foreign matter can get between them and a small leak can result.

Unfortunately, the parts are no longer available, so you'd have to locate them online somewhere. Try looking in the ad sections, here, on RCU. You may wind up having to buy a used carb or even full "parts" engine to effect repairs.

There is always more to the story! I purchased this motor used around 8 years ago and the vast majority of the blemishes were from the previous owner. This was at once a fine running little motor until the chicken stick incident, knocked it clean off it did. I've never removed the spray bar assembly until now was not sure of anything other than it being the source of a leak.

So mine at once looked like yours? What purpose does the internal spring serve?

Attachment 2227372

In my first picture there is a screw and spring combo on top of the carb, what is that for?
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I'm learning pretty quick that is the case across the board for me. I got out of the hobby almost 8 years ago. I had this Super Tigre mounted on an old Hangar 9 .60 Corsair (the one with the horrible retracts) controlled by 72Mhz transmitter and receiver. She sat in my shop since then and would you believe it cranked? I couldn't. The Hangar 9 Mustang PTS fired up and my youngest son is flying it. Eureka!

Now, coming back in, replacement parts for this and that are almost non existent. Upgrading to 2.4ghz is expensive. But...we're flying.

That is the idle speed screw with modern radios just back it out until the barrel is fully closed and set the idle speed with the radio. The internal spring stabilizes,the barrel,it keeps it from bouncing back and forth.

FL, see if you can measure the venturi diameter and the neck diameter.

That would be most appreciated!

As it turns out I had a spare that came along with engine when I bought it! Installed and runs like a scalded dog!

It will idle and transition better if you point the inlet nipple at the rear motor mount bolt.

David

I think it best to start with the orifice pointing straight in as it came from the factory and adjust only if necessary. Many ST engines run fine the way they came from the factory. Just my $.02

Good point. From my time with ST engines the 90's were among the easiest to tune. I ran 14x6 APC on mine and rarely touched the needle. I hope the OP has the same luck.

David

Don't forget that there is a tiny O-ring with a spring behind it inside the needle valve outer shell. You have to look hard to see it if it has gotten hard and is stuck in there.

Like this, and it resides in it's own little pocket.

Your small block Ford equation is more like a 275 than a 255 LOL.

My S90K needed the spraybar adjusted with stock muffler used during the long break-in period, but after about 2 gallons, it ran lean in the midrange with the spraybar adjusted. Once reset to straight in, it ran great. I re-ringed it with a Bowman ring and it ran normal with the stock muffler during the re-break-in. Put a tuned muffler (red Jett) on it and it ran rich in the midrange again. I don't fly this engine, but rather use it on an RC airboat. I prop mine a lot lighter when using the tuned muffler so it gets "on the pipe" in the 13-15k range. Typically I use a 12x6 or 13x5-6. The fuel, prop load, and muffler play a huge role in how the carburetor needs to be set. The tuned muffler provides much better pressure than the stock muffler, so the midrange can tend to run rich without any adjustment of the spraybar from the OEM position.

By my calculation I get 255.2688304 cubic inches.
Radius==1.84
Radius squared==3.3856
3.3856 times 3.1416==10.6362
Times 3" stroke==31.908 cu. in. per cylinder
Times ====255.27 rounded off a little.

I had a ST .90 Diesel conversion, it turned a 14x7 3 blade at 8,500.

I only have one ST engine, a G51 that I used extensively for 8 years and had the ring and bearings replaced. All this talk here is motivating me to build the next plane for it. I plan on building a Sig Kavalier for the G51. Should be a nice combo.