I have a strange problem perhaps someone has seen it before or has some advice. First I'll tell you the problem, then I'll tell you what I've checked/tried so far...

New plane with new engine (Ultra Sport 40 Plus with Tower .46). Engine was broke in meticulously and was running great for the first few flights. It's swinging a 12 1/4 x 3 3/4 APC. Running to max RPM then backing out about 1/4 turn on HS needle yields 11,700RPM. Now here's the problem.

The plane starts and runs PERFECT when sitting on the ground horizontal (in holding saddle). When taking off, and full throttle is hit, the engine will almost die (only with forward movement, not when it's stationary in saddle). If running in saddle, when plane is picked up at ANY throttle setting, once it hits about 45 degrees or less, the engine either dies, or if I'm running it VERY rich, it will increase RPM first, then die.

Now here's what I've tried / checked so far...

First thought was the clunk stuck in the front of the fuel tank. Though it hasn't had even seen so much as a rough touchdown. The clunk was riding about 1/4" off the back of the tank and everything is fine with it.

I tried replacing the glow plug, including trying one with an idle bar (since the engine is inverted), no results.

I tried richening the idle mixture, no results.

I checked ALL the fuel tubing for possible airleaks or holes, INCLUDING fuel tubing inside tank. No leaks found anywhere.

I bypassed the quickfill valve, just in case it was sucking air.. No results....

I pulled the tank and verified no cracks or air leaks.

I checked for any leaks around the crankcase or carb, nothing.

I verified that there are no kinks in fuel or pressure lines. Pressure line was hooked to muffler. Blowing on pressure line does force fuel out of fuel line. Made sure pressure fitting was not plugged.

Changed to a 10x7 prop (same one used for break in), no results.

And now I've run out of ideas... Has anyone seen anything like this before or have any idea what could possibly be causing it? Thanks in advance for any help!

If you're sure the spray bar isn't clogged in any way (try blowing it through with alcohol), it sounds like there might be a crankcase leak. Are you sure the backplate or carb seal don't leak at all?

-David C.

I'm pretty sure the spraybar is fine, I did remove the needle valve, blow through, then replace the needle valve and blow through again... Seemed clear, and should have been after blowing... I'm pretty sure there is no leak around backplate or carb... The backplate is tight, and has never been removed. (and this just started after several flights) The carb is seated and the oring is in great shape and compressed. Would an air leak cause that problem anyway? I know it would play hell with getting the needle settings right, but it should cause problems at ALL times, not JUST when the nose is tilted up right? This seems more like when the nose starts to tilt up it just completely loses fuel. Yet I can't for the life of me figure out why!

Assuming you are using fresh fuel:

Did the engine tend to konk out at the beginning of the throttle or the end (wide open) ?

Did you adjust your idle with the plane right side up or upside down?

How was your transition? Is there a difference with the engine is right side up or up side down?

If you open the throttle slowly up and down, one click at a time, was there any sag in rpm or even konks out after a few seconds? Was that with the plane right side up or up side down?

Looking at the plans of the US+, the carb centerline with an upside down engine is quite a bit lower than the tank, and the tank is pretty far back from the firewall. I am assuming you set up the plane per US+ plans.

Yup, fuel only about 1 week old...

If the plane is sitting horizontal in the saddle, it will not konk out at all...

If I lift the nose 40 degrees or more, it will konk out regardless of throttle setting.

initially plane right side up (engine inverted), though I did try adjusting with it upside down (engine normal) and that made no difference...

No, we tried the same thing with the plane upside down, and same thing, as soon as the nose comes up, it seems to lose all fuel flow...

No sags really, though at one point from 3/4 to full throttle seemed to have little effect... This was correctly later though, I think through HS needle adjustment.

Yes, it is set up exactly as the plans show. The centerline of the tank is on the centerline of the crankcase, but that does drop the carb centerline just about at the bottom of the fuel tank. It's low enough that with the carb open and the plane just sitting on the ground it will constantly drip fuel out the carb. And yes, the front of the tank is probably a good 7" behind the carb.

GregG:

This is the kicker.

If the problem were due to a set up problem it would have been there at the start.

Which leaves us with finding out what has changed.

Cheapest/fastest/easiest: Replace all fuel hoses, the glow plug, and get a fresh gallon of fuel. After checking all the fuel and air passages in the carb.

If the problem persists after this, you may well have had a bad lean run and fried the piston and liner.

Bill.

rusirius,
Did you check the brass lines in the tank or just the silicone? Look for a crack in the hard line, perhaps near the stopper. This can easily be checked by just letting the plane run out a complete tank. If you have a fuel line crack the engine will stop as soon as the fuel gets down to the level of the crack.

Here's my guess....somethings changed....right...?

Your quote...
The plane starts and runs PERFECT when sitting on the ground horizontal (in holding saddle). When taking off, and full throttle is hit, the engine will almost die (only with forward movement, not when it's stationary in saddle). If running in saddle, when plane is picked up at ANY throttle setting, once it hits about 45 degrees or less, the engine either dies, or if I'm running it VERY rich, it will increase RPM first, then die.

Your motor is leaning out....alot of planes when "punched" at take-off will lean out....do to gravity pulling the fuel to the back of the tank....

....or if I'm running it VERY rich, it will increase RPM first, then die.

...it's leaning out....first picking up rpm, then dying....like a plane
running out of fuel....

There's only one built in factor in the plane....designed to offset these characteristics....or laws of physics (if you will)....

....fuel pressure. Your lacking fuel pressure....causing the
funny running. I'll bet your fuel pressure nipple may be
partially plugged. You said it seemed to open....but is it
1/2 open.....there is no doubt, you have a lack of fuel pressure.

Take the nipple out, and lock-tite it back in to eliminate any
pressure loss at the threads....then drill through the hole, just
a bit bigger than the stock hole.....give the tank some pressure.

Assuming that your carb is clean....the tank is close to the proper
position....lack of fuel pressure is the only thing that will result in
the symptoms you are describing.

And....FWIW....you should run that motor on 15% PowerMaster fuel, with a Fox Miracle plug....and a 10-8 MAS prop. That
engine is made to turn....no to lug....with a tree branch hanging
off the front........these are not guesses....your motor will
perform well with these middle of the road....tools. Forget the
idle-bar plug.

Dave.

Yup, checked brass and sil. Everything looked good... and it will still run with barely any fuel in the tank... Basically if it can reach the clunk it will run...

Tank is way to far back and way to high. I would fix those problems first. there should be a big change in fuel settings when you turn the plane over. there should be a big change when you hold the nose up, in trying to draw fuel that far.

I agree Dave, it definately appears to be losing fuel, which means either clunk coming out of fuel, which isn't happening, or the tank is losing pressure. I checked the sil. lines from tank to engine, (pulled them off, plugged one end and blew into the hose while stretching it.. no loss of pressure).. I did pull the nipple and made sure it was open. Everything looked great. I also blew through it and there didn't seem to be any difference in flow between blowing through a straight piece of tubing and the the same tubing attached to the pressure fitting. I have not drilled it out further, which is something I can try, but i don't understand why it would have suddenly changed... Yes, it was a Fox plug originally, but I replaced it with the idle bar plug just in case (figured it might help since the jug is inverted).... You really think swinging at 11700 is lugging? I figured around 12000 was pretty optimal???

There is one other thing I found that I have not tested yet. Though the motor seemed to run perfectly at both hs and ls, according to the manual that came with the engine, for tuning the ls needle the "starting position" that is supposed to be close is with 3/32" between the needle and the spraybar. Mine was set at about 1/64"... It didn't seem to be running too lean, but I've backed it out to about 3/32" and will try adjusting it from there and see if that makes a difference.

Have you tried putting a one way valve to hold pressure in the tank? As stated it sound as if the engine is leaning out. This may also help because the tank is so far back. I also have a Tower 46 and it turns a 12.25x3.75 at 12,300 on Omega 15%. I had a little problem getting the low end set so it would transition between low and high but it runs fine now.

The trouble with using a check valve without some form of regulator is that you will have too much pressure when you go to part throttle. A cline regulator would be just the ticket for your problem.

....opening up the low end needle closer to the factory
recommendation is probably your best move....carb
settings can change as the engine breaks in. Sometimes
a new set-up plane will work fine for a while....and then
heh heh heh....the Gremlins strike....and things get silly
for no apparent reason....

....Hobbsy is right....the Cline pump/regulator will scare off
all the Gremlins permantly....[8D]....

....for Heavens sake....take that JUNKY APC off that thing,
and save it for scaling fish....or digging weeds........
yes 11,700 is lugging that motor....use the 10-8, and it
will pick up revs into the 14K range....and the plane will go
15-20 MPH faster....

....make 100% sure the carb is clean in the nozzle, and the
low speed needle....and the carb is down tight against the
O-ring. I don't know how many times a Fella has had some
problem crop-up....we all troubleshoot the darned thing
from afar....and the Guy comes back a few days later and
says...." I cleaned the carb, and the engine runs Great now,
....thanks Fellas ".

But on the other hand....this is fun....people participate...
and in the end, we all learn from it.

That's what these Forums are all about........

....keep us posted....

If you haven't tried it already. you may want to check if your muffler is loose and losing backpressure. If I remembered correcty, you may get as much as 1/2 lb of untimed pressure off a muffler to the fuel tank. If the muffler isn't tight up against the exhaust or a gasket isn't sealing, you may actually lose that 1/2 lb easily.

The other places to check are the nipples and carb needle recepticle that screws into the carb body. If any of those have loosen up over time or the gaskets are bad, they may cause you to lose suction from the carb.

If all else fails, then run the engine at a higher rpm; they will improve the suction and backpressure tremedously. There may be nothing really wrong with your setup; you may have just discovered the engine's operating envelope as far as fuel draw goes.

Just for the record, I'll give you $5 for the engine.

Sounds quite similar to a problem I encountered with my profile fun fly some time back which originally had the tank buried in the wing. The engine would run great in any horizontal position but as soon as the nose was raised it died. The only way it would run with the nose raised was to set the H/S needle very rich which cut the power significantly.

The folks here were more than helpful in assisting in trouble shooting my problem. After numerous suggestions and as many trials on my part, nothing worked. Then someone suggested I try a test tank closer to the engine, as it was a sure thing that I had a fuel draw problem. l rubber banded on a test tank to the fuselage closer to the engine and presto, my problem was solved .

It turned out that even thought the engine ran beautifully for a short while at first, the clunk supplying fuel was just too far away from the engine when the nose was raised causing the engine to go lean and die. The plane did look quite sleek with the tank hidden in the wing, but it sure fly great with it mounted on the side of the fuse. HTH

If as you say " the front of the tank is a good 7" behind the carb " that means that the clunk is another 3" or so further back which makes for a fairly long fuel supply line for that size engine.

I have an Ultra Sport 40+ with a OS 46FX. Runs awesome, I was concerned about tank location at first, but it has turned out to be a non-issue.

Yeah, I understand what everyone is saying about it being a long draw for the fuel etc... But at the same time if that IS the problem I'm experiencing it doesn't explain why it was working perfect for the first several flights, then just suddenly stopped. It doesn't make sense that it would "suddenly" require a pump to be able to draw fuel that far. I'm gonna swap the engine with another bird and see if the problem stays or follows... If it stays I'm gonna try a new fuel tank with new lines and try it up next to the firewall for testing... If it's still good, then I'm gonna put it back into normal position and see what happens....

I did try the new needle valve adjustments today and with no luck.. the "book" settings were WAY to rich... it's set now running very rich with a small bog in the transition to full throttle, but nothing major... Though i'll wanna lean it out a little more once this problem is solved..

I'll keep everyone posted on tommorows "swapping" and let you know the results...

Refer to post #6 in this thread.

Bill.

Bill,
Right, if the cyl/pis were shot, that would certainly be something that could change, but what I mean is something that would "change" that would now require me to use a pump or regulator... That's why at this point I'm trying to stay away from seeking that avenue. I also don't think there is anything wrong with the liner or piston cause it still has plenty of compression and more importantly will hold the compression. I've replaced the tank with a different one, and strapped the old one to the side of the plane right behind the engine... When I get home tonight I'm gonna run some tests with them and see if either the new tank runs it regardless of being in the same position as the old tank, or if the old tank now works since it has been moved up close to the engine. If the problem persists with both I'm going to look closer at the engine.

Ultimatly....I think moving the tank all the way forward, and
some good fuel pressure is gonna be the correct answer.

You should have the tank fuel outlets sticking through the
firewall....with a foam donut around the front of the tank.

Dave.

No go... I'm still checking a few other things out, but it looks like it's unrelated to the tank location. I've swapped tanks and no different... Then I took a brand new tank as well as the same old tank and strapped them to the side of the fuse right behing the engine... Ran short (maybe 3" each) lines to carb and muffler... Still does the exact same thing... The moment I pick the nose up she dies out on me... I also put a new pressure fitting on the muffler, this one with a much larger inner diameter. As well as making sure the muffler was sealed tight everywhere and no leaks. I'm now going to swap this engine for an OS in another plane... Then see if problem follows the engine... If it's still doing it then it's gotta be something with the engine... I dunno... Will keep everyone posted...

....perhaps an exorcism, then....???? ....

....I'm out of ideas, Dude....

This has been a very interesting thread!

This reminds me of an engine that did the exact same thing. I could adjust the needle valve and get her screaming, but every time it rotated on take-off, the engine would die. As a last resort, I replaced the piston and cylinder. Took care of the problem. Like I said, this was a last resort, because I had good compression. The engine was just "worn-out" and couldn't take the extra load at lift-off, or a nose up attitude.

Now this was a COX TD09 engine, however, it demonstrated the exact symptoms described here. I know that your engine is not as old as was this 12+ year old engine, but it sure makes me wonder if you had a lean run causing your engine to lose efficiency and act like a worn-out engine.

Food for thought, cause it sounds like you've troubleshot about as far as you can go.

Best of luck finding the culpret.