hsukaria

I tried blocking the exhaust with my finger temporarily as I was cranking the engine. That is where I saw that the fuel wasn't getting sucked in, so I suspect that there is a fuel draw problem. I will clean the carb tomorrow. If that still doesn't help, I will mount it on my test stand to verify that there isn't anything still wrong with the fuel tank/tubing.

1QwkSport2.5r

H - what kind of clunks do you use? Felt? Sintered? Regular run of the mill clunks? Perhaps the clunk might be plugged?

downunder

Check to see if the pressure nipple on the muffler is blocked with carbon.

hsukaria

Tim, I checked the clunk to make sure it is not clogged. It wasn't. It is a regular brass clunk.

I took the carb apart and cleaned it. I soaked the spraybar in denatured alcohol for 8 hours and re-assembled the carb

I went to fly the plane this afternoon and had a few deadsticks. I kept retuning the HSN and LSN while thinking to myself that this engine has never been so finicky. But I did finally tune it rich
enough so that it would not quit. I did not see any more fuel bubbles in the carb line.

I came home and read the suggestion from Downunder and went to the plane to check if the muffler pressure tap was clogged. Well, the pressure tap is not clogged, but the fuel tubing was
cracked at the bottom of the nipple, so it wasn't visible until I checked it. That explains the random dropouts.

Well, I feel silly!!! At least I got all the other fuel issues resolved as well (there was a kink in the fuel tubing as it passed through the firewall also). I will go to the local hobby store and buy a whole bunch of new fuel tubing and replace it on all the planes I plan to fly this season.

1QwkSport2.5r

Buy a spool of fuel line, I think the Dubro spools are 50 lineal feet. I paid like $32 at the hobby shop for the spool, has lasted me like 4 years and I have half of it left. Otherwise the stuff is $1/Foot.

My rule of thumb when it comes to an engine that is normally well behaved and suddenly runs like crap is to do the simple stuff first. Check and replace all fuel lines, replace the glow plug if it is more than a season old or if it's been sitting a long time and clean the carb out. Simple stuff first which involves the consumable stuff; fuel line, glow plugs, and O-rings. Only after you've exhausted checking the simple stuff do you then tackle the harder big ticket stuff like bearings and piston rings.

Nonetheless I'm glad you figured some stuff out.

1QwkSport2.5r

For anyone that wants more power from their Super Tigres with round spraybars, shave the spraybar down like the old flat ones that came in some engines. It's good for a 500-800rpm gain depending on prop. This is a spraybar (flat) from my S90 and next to it one from a G51 (round). Both engines are Italian made.
Before:

After:


I used my dremel with a reinforced cut-off wheel, 60 grit sanding drum (small size drum), 120 grit sanding wheel (not the flat disc kind), and a rubberized polishing bit. The spraybar is 4mm thick and the flat part is 2mm thick in the S90 spraybar. The cats eye discharge orifice is slightly wider in the G51 spraybar so I didn't take it down quite as far - 2.1mm. I'll be testing the modification this weekend sometime. This engine (G51) is going to get some timing modifications yet, and perhaps more carburetor modifications. It runs nearly identical rpm to a low runtime TT .46 using a .46 sized Jettstream muffler (Red) and the flat spraybar. It might just become an FX/AX killer.

Mr Cox

Is the midrange still tunable?
That's one of their best features with the carb I think. Ones the carbs are dialed in properly, for a specific fuel, they deliver a very smooth running all over the rpm range.

The X.11 has a very large intake bore from the factory, with a removable restriction in it. So there I don't think that there would be any gain to flattening the spraybar...

1QwkSport2.5r

Yes the midrange is still tunable. I ran the S90 spraybar in the G51 on several props and IIRC needed to adjust the midrange (rotate spraybar about 5 degrees off straight in) on one of the bigger props, a 12x6 I think. The 13x4W had a very slow spool-up and was quite rich in the midrange but I didn't bother adjusting it because it will never be run with a prop that big. It turned 10,800rpm on the 13x4W APC on 5% fuel and the S90 flat spraybar.

I would think this modification would not be wise to do on small engines with big bore Carburetors unless you're running a bladder or a pressurized tank. Fuel draw will suffer I'm sure. If the G51 spraybar fits the S29 carburetor, I'll test run the S29 on it. It too has a round spraybar which I think really holds it back.

The G51 and S29 carbs never needed midrange adjustments in stock form or on tuned systems. The S90 suffered a very rich midrange until I burned 2-2.5 gallons of fuel. The spraybar was adjusted 30-35 degrees from straight in to clean up the midrange. Now it's back to straight in and running on a tuned muffler.

1QwkSport2.5r

Tested the G51 today. Jettstream muffler (red), 10x6 APC, 5/20 fuel, OS F plug, modified spraybar. Best peak rpm I got was 15,570rpm. It ran clean at 15,200 but loaded up during prolonged mid-throttle operation. Lowest stable idle I could get was 2,200rpm but it liked 2,400-2,500rpm better. I still have more work to do to get it throttling perfect but the results are promising. Picked up 400rpm from the round spraybar.

jeffie8696

Impressive

1QwkSport2.5r

I thought so too. I have more work to do with it..

Charley

My Feedback: (2)

Not enough prop.

CR

1QwkSport2.5r

It's not even getting on the pipe.

Charley

My Feedback: (2)

Are you sure? What's it turn with the standard muffler? Just curious.

CR

1QwkSport2.5r

Stock China muffler on the same prop, fuel, etc. was 14,970. Bob Brassel said to get the most from this pipe, it needs to be running at least 15,500rpm to be getting the best benefit of the pipe. 14,970 is with the S90 flat spraybar. Stock round spraybar it ran 14,550.

aspeed

I would be more interested in what it turns with an open exhaust. Mufflers are almost always a loss, open is kind of a starting point, and a pipe is then adjusted to improve on the open exh. rpm IMHO.

1QwkSport2.5r

I was testing against my runs I made using the Jettstream and the thin spraybar. I will have time to run the engine again tomorrow so I will test it with open exhaust. I was going to do it yesterday but ran out of time.

1QwkSport2.5r

Open exhaust on an APC 10x6 prop and mc59 glow plug I peaked it at 15,350rpm on 5/20 fuel. With the Jett muffler I couldn't shake the wet midrange. Open exhaust the midrange was okay and on the stock type China muffler it transitioned fine with the spraybar straight in. Peak rpm on the stock muffler was 15,330rpm which I was surprised by. The volume of the China muffler and the Jett muffler is about the same.

Edit: Running my TT pro .46 side by side. Open exhaust on the very same glow plug as the G51 and same 10x6 prop I got 15,350rpm and on the Jett muffler I got 15,600rpm.

Charley

My Feedback: (2)

Sounds like the Jett is coming on line somewhat. Otherwise it wouldn't be rich in the midrange. When they come on the pipe they need more fuel; come off it and it's rich. You could go down in pitch, say a 10x5,& see what happens. Is a couple of hundred RPM all that important or are you just having fun? I used to play like that when I was racing warbirds.

CR

1QwkSport2.5r

I'm messing around with carburetor and timing mods to increase power on smaller props. The TT pro has a 7.5mm carb and the ST carb is 8.9mm. Based on the open exhaust and Jettstream tach readings, it doesn't seem to be doing much. I think the Jett muffler provides too much pressure to the tank in the midrange on the G51, it runs perfect and smooth on the TT. Both engines are timed almost identical, about 154* exhaust timing. It is nice to see the ringed .51 hanging right with a good ABN .46. The .46 turns a 9x7 at 16,800rpm today on 5% fuel. I'm going to mess with the G51 some more and see if I can get it on the pipe and not be soaking wet in the midrange. It didn't quit at all, but holy smoke screen Batman! I think the bugs are still gone.

What my goal is is to get this poor G51 to turn 16,300-16,400rpm peak on a 10x6 which I think is feasible with more timing and the right exhaust. 165-170* would be more ideal I think.

JeffH

My Feedback: (43)

Does anyone make a flexible header for the ST 3000? I have a very narrow cowl and need to put the muffler below the engine(inverted engine) so that I do not have to cut a hole in the side of the cowl. I really do not want to run an older Bennett style "muffler" since they are soooo loud.

hsukaria

After a year of my G51 being shelved, I re-installed it in its original plane and will use it to train my son to fly this summer. Should be fun!!

1QwkSport2.5r

Yours is coming off the shelf and one of mine is going on the shelf. LoL. My ST S90 is getting yanked off one of my boats and is being replaced with something else.

I do think I'm gonna get my piped S29 going this year again.. Hopefully get the new ring sewted and get her hummin good!

flyingagin

I am building a new bird for my ST .90 from 2 salvaged wings (bi plane). Should power 90+ square inches nicely.

Ken

Charley

My Feedback: (2)

Er, did you mean 900+ ?

CR