I have a Great Planes .40 size Ultimate Biplane with a Sullivan slant style fuel tank and an OS 46 FX engine with a Bisson Pitts Muffler attached to it. I seem to have a problem somewhere in my setup on my plane because for some reason when I go full throttle it almost always shuts off completely. It doesn't sputter or anything of that nature. Just dead. I've tried putting on a new OS 46 FX to see if it was a problem with the engine but it did exactly the same. I have the new engine on a H9 US40 and it's doing great. I've replace all of the fuel lines and even went away from the dubro kwik fueler and went with a 3rd line for filling and that hasn't helped any at all. I've even had the most respected engine guy at my field look at it and he is completely stumped. Has anyone out there had any similar problems? More importantly, does anyone have a good answer to fix this problem?

Are you running the same muffler in both installations. I've seen others say that some PITTS style mufflers do not provide adequate back pressure for the 46. You may want to try plugging one of the outputs (if there is two) or fitting a smaller diameter tube or extention.

I have a 46FX with the stock muffler on a Sig SE and it's been great.

REgards,
Lee

Well, I sent a G90 back to Hobby Services twice. Turns out my fuel line from the tank to carb was crimped. It did not look it but it was enough to cause it to run okay on the ground but overheated within a minute of flight. I attached longer fuel line and it ran fine for the last 6 months.

Check your clunk in the tank and the tank's seals.

Other than that I'd start opening the needle or buying Thunder Tiger.

I see a potential for cooling problems resulting in overheating and the engine shutting down.

The Ultimate cowl needs plenty of air exit opening area for cooling where as the Ultra Sport engine hangs out in the breeze.This could be the difference.

It ain't the engine - its something you're doing wrong or have failed to notice.

bingo- we always seem to blame the engine. start at a point eliminate one thing at a time and you will find your problem. ps every body so far is spot on, its for you to find which one.

Somehow your engine is starved for fuel at full throttle. I would tend to agree about the Pitts muffler and reduced pressure to the fuel tank is causing a lean condition at full throttle. You may just need to run a little richer or switch to the stock muffler.

Lets not forget the glow plug in this situation. Go with the OS #A3 for rock-solid performance on this engine.

I had similar problems when my 46fx was installed inverted. It was flooding out. It ran fine after installing it glowplug up until I crashed it hard. Then it started acting the same way in a new plane until I discovered a cracked crankcase along the engine mount lugs. I replaced the crankcase and now it works well up, down and sideways.
A big Red X
Fred

You say it's not sputtering before it dies, this eliminates it being rich.

If the revs fall off quick as you go wide open, but you can catch it if you bring the throttle back down real fast, then it's real lean on the top end.

If the mix is fine, it just flat dies (idle to full) in the air or on the ground and has to be run as lean as possible to stay lit, try a fresh jug of fuel and a new A3 at the SAME time.

The bad fuel will ruin a new plug until it's run on fresh fuel for at least 3 tanks.

Kirk

Thanks for all the help guys. I'm going to try putting an extension on my stock muffler so I can put that on and see if that helps clear things up. Wish me luck. BTW: I have already tried the whole new glow plug, new fuel, adjust the needle thing. I spent 3 full weekends at the field working on that and still have everyone stumped. :stupid:

beardking,

You might want to check your idle mixture setting. If it's too lean, it can interfere with high-speed fuel flow. This would result in the engine shutting right down when you advance to high throttle settings.

Richen the idle mixture half a turn to a full turn, start the engine at 1/4 throttle, and see if it will advance to full. If it still cuts off very cleanly, then it's likely you have a fuel feed problem of some kind, such as the many posters have said above.

If it's in a cowl w/ pitts muffler, fly it with the same needle settings with, then without the cowl. If the top end gets real rich without the cowl, you've found the problem.

If it's not getting enough air, the top-end will have to be run very rich to keep cool at full throttle. This kills mid and transition.

Also, when an engine is way too hot, it won't sputter before a flame-out like it would if it was at normal temp.

Hope this helps!! Kirk

Hi!
The first thing you should do is to check if the fuel is coming out from the tank! Just fill it up and see if it comes out in the fuelline going to the carb....if it comes out real easy then connect the fuel line to the carb and try to start the engine!
No! do not put on any silencer extensions yet!!! It will increase backpressure and heat in the engine, which is not good! Later when you have the engine going maybe you could try it.

Some recommendations!
Use a 11x6 APC prop.
5-10% nitro
OS 8 or Enya 3 glowplug!
8-10oz fueltank.
Use a 12v 7-12A motorcycle batteri for starting and an automatic glowdriver to get the volt down to 2v for the glowplug.
1,2 v NiCads are useless...more or less anyway, only god for experienced flyers!

Regards!
Jan K
Sweden

lose the pitts muffler if possible.. had one on my .46 wouldnt run worth crap.. took it off ran fine.. plus maybe tune it up if that dont work.. with the throttle halfway open.. screw the second needle in to about 1/16 of the spraybar and tweek from there .. had to do that also.. os instructions are wrong. took the motor to the lhs here and the german guy tuned it up in 30 seconds... runs like a champ again..
just a thought