Ok, I have a new 150 engine, just about broken in, the thing is awesome except when I go inverted it cuts back like it wants to die, (1/4 to 1/3 throttle) I can give it full throttle and keep it running but that is not something I want to or can do with all moves. It also looses RPMs on vertical for a moment.
I have checked the gas tank, twice. don't get no better. 50oz, large clunks, copper tube in tank to keep clunks from going forward, vent line open and unobstructed.
I have richened the low and high needles a 1/4 turn, no help there either.
Very annoying, Any help would be appreciated.
Thanks,
Wayne

have you tried leaning the main needle? You may be too rich.
It also often helps to connect a vent line to the carb vent hole on the stamped metal plate, and route that in a prop blast shielded "vent box" with constant pressure. A small balsa enclosure in the fuselage will do.
Sometime it is enough to rotate the stamped cover, or cover the vent hole with a prop blast shield.

Thanks Preivers, The carb has a prop blast shield with the pressure tube already attached. Came from the Factory that way. I will lean it out a little more, but i'm a little hesitant.
Again thanks.
Wayne

You won't hurt a gas/spark model engine swinging a prop by running it "too lean". Why? Because it won't run "too lean". That is glow fuel thinking. Get rid of it.

Nope, I ain't gona say it.

What!!????

It sounds like you have not fried a gas engine yet. They can run too lean and damage themselves just the same as a glow engine.

Back to the original problem of running erratic running while inverted there is one more thing to try. Get a couple of helpers that you trust and fire up the plane inverted. If it is still erratic it is most likely a mixture problem. If it runs smoothly then it is still an inflight airflow problem affecting the carb.

If you have a couple of friends hold the plane inverted and it dies, wouldn't that be a carb problem rather than a mixture problem? The mixture should not change with attitude. I'm talking no air flow at all here, static on the ground.

That would be a fine check.
And yes, a gas engine gets damaged when too lean. On the lean side of best power, combustion speed drops, and first the engine goes to best efficiency. When leaned still further, cylinder and exhaust gas temperatures rise dramatically, resulting in seizing pistons or piston lubrication film breakdown. The end results are the same: a fried engine.

Joe, I have thought of that. Even ask a couple of friends at the field to hold it inverted and let me crank it. On a 46% Ultimate with a real bad (as in good) 157 on it I cannot get any takers.
I just cannot understand it, it is as smooth as can be idle to WOT on the ground and in the air flying level, go inverted, for a harrier, or an inverted pass and it scares the help out of you.
Going to keep leaning it out just a little bit more. ( while watching the temp)
Wayne.

Lord give me strength to keep my fingers still and my mouth shut.
Still ain't gona say it.

Wayne, I'll have my buddies tip my 29.1% Edge 540 over and see how it runs at lower throttle settings. I'll let you know the results, won't be anytime soon, got the kids this week. Maybe next week.

BTW, I'm having this same exact problem on my DA 50, it seems like people all over the place are reporting this on their gassers of all brands. I had a close call a week ago, inverted harrier, not to far above a tree line, flamed out. Got it rolled upright and floated in. Could have been so much worse. I covered the hole in the firewall and put a wind block on the diaphragm plate like DA asked me. I haven't tested the inverted harrier at idle yet (I need the field cleared to do this).

Joe

A friend with a 1.60 MVVS had the same problem. This was solved by adding a backward turned scoop on the carb mouth, so no airblast or prop buffeting could enter.
Walbro carbs work great on chain saws, but when unpredictable airflows enter the picture they can be a beast to set up properly.

preivers, It already has a prop blast shield. A back wards turned scoop just as you described.
Joe, Thanks a lot, let me know what happens. I do a lot low and close to the ground, or should I say- I did, Glad I tried all this 2 mistakes high, as stated I am going to start leaning it out a little while watching the temp. Hopefully that will help solve this.
Again, Thanks.
Wayne

And anyone that knows Artisin, don't let him tune a gasser, make him take it to Macs' or bring it to Macon, we will try to help him from frying it. Or is he just funning me. [X(]

Wayne I have hear this problem can be caused by improper pop-off pressure in the carb's diaphragm. I'm tempted to check and adjust mine.

Wayne..try this..it eliminated that problem with both of my DA 50's

http://www.troybuiltmodels.com/CarbPlate.htm

or this http://teamsala.tripod.com/teamsala/..page down about halfway

Problem solved, leaned it out and re-calibrated the fuel metering. Flys GREAT now.
Thanks for the help.
Wayne

Wayne,

Can you be a little more specific on what you did? Which mixture screw did you lean out, and what is " re-calibrated the fuel metering"?

Chuck

Yeah I want to know more about the re-calibrated metering. Did you adjust the spring tension to set the pop-off pressure?

Would love to hear too.

Karol

Low end needle turned in 1 1/4 turns, leaned the low end out.
Replaced the spring on the fuel metering needle attached to the pressure diaphragm, with one with a little more tension. ( pop-off pressure). I do not like stretching springs, they tend to go back.
That is what I refer to as a recalibrating fuel metering.
Sorry I confused with incorrect terminology, but I come from an exotic engine
(Flattering name for them da** European Engines), tuning and building background.

I think we're all assuming that you mean you "ended up AT 1 1/4 turns" OUT from closed on the low speed, surely. And a longer spring DECREASES the pop-off, correct?

Those two things would seem consistent with info in other threads, but would like you to confirm, please??
Thanks.

Do you need a special tool to exchange the spring?

aerobob, you are 100% right.
Again I apologize for the terminology.

Josey, you will need a small Phillip screwdriver. And quick fingers.

Wayne,


ILLEGAL to SHOOT them!!! Darn, I did not know that. Can you get a licence?
Thanks for the info.

No problem, Thank you.... just wanted to be sure.

Now - where does someone BUY "different length" springs for these???

Longer spring increases pop off pressure (Do this if it runs too rich).
Shorter spring decreases pop off pressure (Do this if it runs lean).

If you think about it, the high pressure means the spring tension is too high (cut it). Low pressure means the spring tension is too low (stretch it or get a stiffer one). So the fact that Wayne leaned the low needle AND used a longer spring seems like it's backwards. I'm a little confused.

It's just past half way down on this web page:

http://www.geistware.com/rcmodeling/...n_pressure.htm