andrewskj

I just finished a new U can do SF but having problems with my engine and was wondering if its because of the position the engine is in that causes the problems . I changed the tank just for good measure , run it in on test stand , use power master 15 fuel even tried another fuel. I also went to a K$B idler plug . the engine starts and runs great for a few min however if I go to mid throttle and stay there a little it dies when i advance to full.throttle . I ve tried to reset high end and low end but still problem there . could i perhaps have a bad carb ? has anyone had this problem with this set up ? Im going crazy because I have not gotten to fly the plan yet ... I have the same band engine in another plan with the engine up right and it works flawless. Could the barrels inside the carb be in wrong position ? I would not know how to reset them unless you can tell me how to do it..I did notice that some fuel drilling out the muffler and last but not least i notice it loads up in mid range and i think that is what causes it to die even if I let it run mid throttle it will die . I would really appreciate and help on this matter and I want to thank you in advance .

bruceal

I would say that the low end is too rich or too lean. It depends what it does when it quits. if you try to open the throttle and it sputters, it could be too rich, if it shuts off sharp it could be too lean. Try the pinch test. If you're not sure what that is, it's just pinching the fuel line while the engine is at idle. The rpm's should rise before the engine quits. That's what I would look at first.

hsukaria

First, adjust the high speed needle to achieve peak RPM's at WOT. Do not back it out to richen yet, do the pinch test first. With the pinch test, the rpm's should rise at most a little or not at all and the engine quit after a while. If the engine speed picks up noticeably and runs a long time before quitting, then it is too rich. If it quits soon after pinching, then too lean. Adjust the low speed needle accordingly and re-run the pinch test. When the pinch test is set, do the throttle up test as described above. Once satisfied with the setting, go back and richen the high speed needle a bit. Then re-check the idle, transition, and WOT for good performance.

The carbs on these engines are perfect, unless you have a bad o-ring. The o-ring on the high-speed needle on my 55AX tore up within the first couple of years of use. So check that o-ring and the o-ring at the base of the carb. Replace if they look bad.

By the way, what prop are you using on this engine? Is it within the recommended range by OS? That can also mess things up.

tdevince

Try a new OS glow plug also. Had a similar problem on an OS61. Changed the plug and all was well.

Tom

gdwrench

I'm having a similar problem with my 55ax, after getting the engine warmed up and running for a time, I'll go from idle to full and sometimes it will cut out but not all the time. Other times I'll go from full back down to idle and it will cut out.... very inconsistent. I've tried all needle settings till blue in the face lemme tell you

Tried new plugs, I've got new fuel, prop is a 12x5, tank is at the right height and I'm using yellow fuel tubing which I believe to be 3/32. I'm becoming disheartened cuz I don't want to fly this thing dead stick, plane and engine are both brand new

When looking at plane from the front the carb is at 8 o'clock if that's an issue

A. J. Clark

Try a little richer fuel setting. Especially the idle.

gdwrench

Thanks for the reply AJ.... The high end I have set to "tone" minus a couple hundred rpm. The low end I do have slightly lean but if I richen it, it will start to load up with 30 sec to a minute of idling and lose transition response, again, frustrating

Should I try an F plug perhaps? Larger fuel line? Tank is at a good level, the lines from the tank are 6 to 7" I believe and seem to be getting enough fuel to engine. I'll try another new #8 today and get my temp gun on it and see what happens

A. J. Clark

A new engine will run a little leaner each flight until it broken in. The high end needs to be checked each flight for the first few flights. Probably first ten flights.

I like to set the idle a little on the rich side. If you get a lean run for some reason you can pull the throttle back to idle. With the idle a little rich this helps cool the engine and keep it running. Which will give you time to land. If both high and idle are on the lean side probably end with a dead engine.

tedsander

Old traditional recommendations were to have the spray bar in the carb about 1/4" above the centerline of the tank, to avoid fuel draw problems.
An engine mounted upside down (more or less) is prone to having the fuel tank trying to drain into the carb, due to gravity. More "head pressure" than is optimal. Hence the fuel buildup in the muffler, and likely dripping out of the carb. And the very touchy needle valves. In flight, great bank angles, or flying inverted, totally change where the tank is in relation to the carb, and with the gravity pressure gone or reduced, the engine gets too little fuel, at worst causing a seize up due to being too lean.
Sometimes marginal problems of this sort can be dealt with just by a different plug, or putting a vertical loop in the fuel line (acts as a mini-reservoir) to help smooth out the pressure variations. I've even seen guys try using a 1 oz tank, fed by the main tank, mounted in a better position. No idea how well this actually worked, though....
The real cure - figure out how to drop the tank lower, or raise the engine higher (either move the whole engine up, or rotate it to get the carb higher). Even a little bit may do it. You may want to explore different shape tanks, and get one with a lower height (but wider/longer so you get the same capacity), to get the effective centerline lower.

And...you are compounding things with a new engine, many of which will tolerate a "bad" tank position after they are broken in, but can be very fickle early on.

rogergh

My Feedback: (3)

[
Had nothing but problems with an os engine mounted inverted in a u can do. Finally mounted it horizontally and all problems resolved. No doubt tank position is the issue.

Roger



QUOTE=tedsander;12634914]Old traditional recommendations were to have the spray bar in the carb about 1/4" above the centerline of the tank, to avoid fuel draw problems.
An engine mounted upside down (more or less) is prone to having the fuel tank trying to drain into the carb, due to gravity. More "head pressure" than is optimal. Hence the fuel buildup in the muffler, and likely dripping out of the carb. And the very touchy needle valves. In flight, great bank angles, or flying inverted, totally change where the tank is in relation to the carb, and with the gravity pressure gone or reduced, the engine gets too little fuel, at worst causing a seize up due to being too lean.
Sometimes marginal problems of this sort can be dealt with just by a different plug, or putting a vertical loop in the fuel line (acts as a mini-reservoir) to help smooth out the pressure variations. I've even seen guys try using a 1 oz tank, fed by the main tank, mounted in a better position. No idea how well this actually worked, though....
The real cure - figure out how to drop the tank lower, or raise the engine higher (either move the whole engine up, or rotate it to get the carb higher). Even a little bit may do it. You may want to explore different shape tanks, and get one with a lower height (but wider/longer so you get the same capacity), to get the effective centerline lower.

And...you are compounding things with a new engine, many of which will tolerate a "bad" tank position after they are broken in, but can be very fickle early on.[/QUOTE]

gdwrench

Well, once the engine cuts out there is not a consistent drip of fuel coming out of carb in fact, I do need to prime engine to get it running (cold). "But" unless I have the low speed needle excessively leaned out it will load up on idle and have very poor transition & cutting out comes into play.

The plane is cowled so I can't change engine position. The tank is oval in shape so I could try to lay it on its side if that can make a difference? The tanks platform is established and I don't see a way to alter it. I'm also going to get a couple F plugs today so I can give this thing another shot tomorrow when I have time.

I really appreciate the responses as it's giving me hope that I can get something figured out here so I can fly this thing with reasonable confidence of not going dead stick

A. J. Clark

Another way to go at it is adjust both low and high setting just a little rich. Then make 4- 5 flights at full throttle or close to full throttle. This will help break the engine in and should help the transition from low to high throttle.

tedsander

I downloaded and looked at the plane's manual. I'm assuming you mounted things per their instructions. While the carb is below the tank centerline, it isn't extreme. I'd go with what the others are saying - your engine isn't broken in, and you don't have the needles set quite right. Do as Hsukaria advises, and do the "pinch test" to get them right on. This is essentially an ABC engine, so should be run pretty close to normal operating temp's to break in correctly. You can be a very slight rich, but not much, or you will have to prolong the break in when you do fully lean the engine in. Go fly, but be gentle - no prolonged verticals, no attempts to hover, etc. Save that for later. It shouldn't die at any throttle setting, but until broken in, it may run rough in some situations. Probably too late, but for the first couple of flights, alternate between full throttle, and reduced, to get it up to temp, and then allowing it to cool off a bit. After a couple of tanks, start mildly stressing the engine with loops, and later stall turns. As you get toward 10 tanks, it will run better and better and you can be more aggressive. AND it will tune better, and hold that tuning better.
Periodically check all bolts - head, backplates, front plate, etc. for tightness. Especially when new, the heating and cooling cycles can loosen them up, again making starting/running very problematic. After the break in period, this will no longer be an issue.

gdwrench

Great input guys, much appreciated... Ya might be on to something here with the break in period. I would guesstimate total of fuel run through this thing to be about 3 - 3.5 tanks of fuel with all the fussing I been doing. Going to bust it down tomorrow and check screws, I did notice the engine is moving as if the motor mount screws have backed off somewhat so I'll walk the whole plane over

I did get those F plugs today plus a new gallon of fuel and a couple of different props

tedsander

Don't mess around with props yet! Pick a size that is within the range noted for the engine, and stick with it for the break in period. Stick with the same brand, as despite what they say, there is significant difference in the load from one brand to another. Ditto on nitro % of fuel (even better, stay with the same brand, all the way through break in!) Changing either will change the temp the engine operates at, which means all the metal parts will expand a different amount. Even though the engine is machined to a fantastic degree, it needs that final "polishing" for the piston/sleeve to get the perfect fit. Changing things can result in different wearing, resulting in an engine that might not ever be at it's peak. No, you won't ruin it, not nearly. But it may not ever be as good as it could be. After it is well broken in (at least a gallon) then you can start changing props or fuel to see what works better.

Break in is terribly frustrating - you want to see what the new plane can do - but one just has to restrain, if they want an engine that performs as it should, and lasts as long as possible.

At least it's not one of the really old fashioned iron ringed and sleeved engines. Those demanded a full gallon only on the ground, before a first flight attempt!

gdwrench

I see your point here and it makes good sense, I will do this but I think I'm going too run a couple tanks on the ground here before I venture out. I thank you and Ted for the helpful information.

I did do some things to hopefully help going in the right direction... I pulled the tank out and realized how long my fuel lines actually were, probably around 9 or ten inches as I was attempting on keeping the fuel supply closer to CG. The lines being 3/32 at that length makes me think that could be improved upon. I did lay the tank on its side and allowed it too slide forward and shorten the lines by about 4" and upped the diameter of the fuel line to 1/8", the reduced restriction is notable.

And yeah Ted, I won't make any other of those changes moving forward, I didn't get to run it today as it's a rain out.... we'll see tomorrow

tedsander

Yes, too long a fuel line will cause issues too! Hence why there was a market for Perry pumps, YS Engines with their built in pumps, etc. Fuel draw is just not great (especially when going vertical!), so one generally has to have the tank closer to the engine than might be desired. Your changes should make a big improvement, and not result in any very noticeable CG changes in flight. Maybe a click of trim, at the most.

Ditto on the rain - and cold. Supposed to be only 40 degrees tomorrow, and raining. Between that and the field shut down due to Trump making a stop today...it looks like my season is coming to a rapid end (will be out of town until almost November).

tedsander

One other tip - after doing the pinch test and setting things, and verifying that after a prolonged idle the engine will respond to quick acceleration, also do the very traditional "Go full throttle, and point 'er at the sky while holding" test. Just to verify that the engine doesn't sag when the plane goes vertical. Go a click or two richer on the high speed, until it doesn't sag, if needed.

You've had more than enough time on the ground, these engines really need to be subject to real conditions temperatures to break in correctly. So get tuning as good as you can, and go fly. Full throttle mostly is best. As said, gradually introduce verticals (loops, stall turns, etc.) with each subsequent tank full. You likely will have to do very small adjustments to the carb as it breaks in. OS says 10 tanks should pretty much do it.