ro347

My Feedback: (13)

I have recently started flying an OMP ProYak which is great fun! For power I am using an OS 55ax with OS F plug and Xoar 13x4 prop. My problem is that I am only getting about 7 minutes on a 350cc/12 oz tank. This seems really low to me. The engine has about 1 gallon of fuel through it now. What could be the problem here? This seems very low in terms of fuel economy to me, but I havent flown a 2 stroke in about 3 years.

Any guesses?

jester_s1

You should get 10 minutes out of it unless you're flying hard the whole time. Have you leaned out your low end enough? What's your tank setup?

Charlie P.

How much fuel is left in the tank after a flight? By visual inspection, that is. You ought to be getting 10 or 12 minutes - unless you're at full throttle often as Jester said. Or burning very rich.

If you are doing hard maneuvers or the klunk isn't positioned well you could be leaving a few ounces in at the time she sucks air. Also, a fritterred klunk leaves more in the tank than a solid one with a single hole.

RCVFR

My Feedback: (7)

That's really unusually poor fuel economy. Have you checked to see if you are actually burning the full tank, or possibly you have a leak in the fuel line that lets air enter at about the time the fuel level gets to the position of the leak. Check the plumbing.

hllywdb

Another thing to check is your vent setup, to make sure you are starting with a full tank. If the vent is too low in the tank it will not fill all the way. Same with the pickup, to make sure you are draining it all.

How many rpm's are you getting? I usually get over 10 min on a 10oz tank with my 55ax, but that is spinning a 11X7, which is better on fuel.

mclina

I agree, you should be getting much longer flights. I have the same prop and engine on my Mojo 40, with a 10 ounce tank, and I am flying 15 minutes easy. I am also guessing that you are running rich.

It's hard to imagine that you are flying that plane full throttle for 7 minutes. I am very rarely at full throttle on mine, and then for very short bursts.

Good luck

rlipsett

I get over 10 minutes with an 8 once tank but I am not hard throttling it all the time. check for pinhole leaks or weaping around the bung hole

bigdanusa

On my phoenix extra 300 I noticed the fuel economy is getting better with the 55ax and a pitts muffler on it after it was broken in and a few flights on it.

big dan

Augie11

If the engine is running well you mostlikely don't have any leaks. I would go along with checking the tank visibly to see if it's getting completely filled. I get about 10 minutes on a 12oz tank with plenty to spare on my .55 AX's. Get a little more fuel through the engine and your economy should improve.

Gray Beard

My Feedback: (-1)

I usually figure one ounce per minute of flight just as a rule of thumb when buying a tank. It works out pretty close to that most the time. We used the OS .55 AX in the 60 size pulse using a 12X4 APC and were getting two minutes per ounce of fuel?? That was the best I have ever seen with a small engine. The Pulse isn't a YAK though and even doing stunts it isn't at full throttle all that much. Sounds like your tank isn't getting a full load or not getting all the fuel out of the tank as mentioned. It does sound like you have it tuned a bit rich too?? Throttle control means a lot when figuring mileage.

jester_s1

If you happen to be using a uniflow setup that can blow a lot of fuel out of the muffler when you let off too.

ro347

My Feedback: (13)

Thanks guys. I will take a look at my tank setup. I will keep flying it to get more fuel through the engine and see where I end up after another 1/2 gallon.

I was also wondering if the prop was too much for the engine and over working it. Seems as though many others are running the same prop/plug set up with good results. So it must be something else.

As far as fuel levels go....being that its a profile, its easy to see. After 7 minutes if flying...there def isnt enough left to even say I have a reserve amount left.

Seems like a great engine, good power and very quiet. Dont even have to use a starter to get it going. Just want to get this figured out.

jimmyjames213

My Feedback: (2)

i think what you should do is get a rpm number for your engine/prop combo that will tell a number of things.
a whole bunch of things could cause that
prop to big
bad plug
inproper tuneing
low range too rich
a combo of the above

edit

im thinking your prop is too big and your idle is to rich, my new ax55 had a very hard time turning a 13x4. i would try a 12x4 or 12.25x3.75 and see if that made a difference.
from the factory the idle is set very rich, maybe since your useing the f plug its hard to notice the rich idle cause it doesnt snuff out easily????? im just speculating here. have you tuned the low end yet?

ro347

My Feedback: (13)

I retuned the engine when I got it. I will try retuning again as its had almost a gallon through it so far. If no change I will change prop to a Xoar 12x4 and see what happens. I know I had the fuel economy problem on a saito a couple of years ago. It was swinging too much prop at the time.

ameyam

I am no expert on prop-engine combinations but (if I am not mistaken) the 55AX has a recommended prop of 12x7 or 13x6 so it should handle 13x4 quite well. I have one on my Reactor with 13x4 MAS K series and it does quite OK. I get about 8 mins at full throttle running rich (break-in) and about 10-12 mins of "normal" flying. I usually last about 8 mins but have set the timer for 10 mins on my TX. I like to land with a minute or so of reserve for a TOGA (Take-off & go-around) if needed. The 55AX should not consume that much fuel unless you are running rich and / or at full throttle for extended durations

Ameyam

CGRetired

My Feedback: (1)

You should be making minor tweeks to the tune at the beginning of each flight day, and as weather conditions change during the day. I have an OS .75AX on a Goldberg Skylark 70 and it has a 10 ounce tank. I time it for 9 minutes and then promptly land, and there is still fuel in the tank.. granted, not much, but there is fuel in there.

As suggested, make sure you tune it for optimal, or peak RPM then back off about 1/8 of a turn or so to richen it up a tad, then fly it that way.

You may want to turn in your HS needle all the way in, back it out about 2.5 turns, and re-tune your high-end again.

And, I'm not sure about that prop.. I do have an OS 55 AX but can't remember what prop I have on that engine. I am spinning a 14.4 on my .75 and it is way to little pitch.. (I chipped the original 14-8 and the only replacement I had was that 14-4 and I don't like it.. way to loud and no bang for that buck, for sure). I also have three OS 1.20 AX's and all three easily turn 16-8, but that's not the issue here.. I wish I could remember what's on that .55, though.

CGr.

tonyob

I've encountered the same problem with an OS 46ax. This motor is 2 years old, about 6 months ago I put it in a new plane with a tank that was smaller than previous planes but not what I'd call tiny.

I didn't take to the plane very well initially but timed my flights and after one particular 10 minute flight, kept the engine running and pushed it at full throttle on test stand to see what my total flight time to out of fuel would be, I ended up with 14 minute flight time.

Once I got quite used to the model, I changed my flying style from running at about 2/3rds throttle to wide open throttle. My flight times dropped to 7 minutes and after that very little fuel was left in the tank. I don't believe my mixture is over rich, the main needle setting is about 3/4 turn out from fully closed.

Discussing this with another club member, he also notices that his fuel consumption drops significantly when flying wide open throttle.

hsukaria

Somebody mentioned it already, but the Type F glow plug is hot, meant for 4-strokes. It may be that you have tuned the engine extra rich and not realilzing it. I would put an OS #8 plug and re-tune it.

racelikustolit3k

My Feedback: (73)

you nailed it buddy, running an F plug on a 2C is wrong wrong wrong, that plug has very robust coil that is built to stay hot, while the 4c engines take quite awhile to to fire again unlike a 2c.. so the plug is really eating up your fuel to compensate for it

swap to a #8 plug and watch how drasticly the engine will change because of being grossly RICH and it was stated earlier try and run a 12.25x3.75 apc prop, those are great for profile and funfly planes ( it really calms that engine down while harriering, rolling H, and hovers..)

good luck


RACE

freakingfast

My Feedback: (3)

I have several 55AX engines, set-up for speed, sport and 3-D. I have found this engine to be the most efficient glow fuel engine for the amount of work done. I'd think there's something wrong with your tank setup. Either your not getting it totally fueled or the vent is submerged as in a uni-flow setup and when you get off the throttle the excess pressure in the tank, dumps fuel out the muffler tap. By the way, I have found the an APC 12X5 works better than a 12.25x3.75 or 13X4...at least for me. I don"t run four stroke plugs in it OS#8 or K&B HD[sm=thumbup.gif]

KWJ48

I have 2 55's, both on profiles, both running mas scimitar nylon 13x6 props, both running F plugs, I have my timer set for 15 minutes. and still land with fuel. I say lean it out some.

zac137

I agree with everbody else. I think it is too rich. I have a 55AX on my Mojo 40, with an 8 ounce tank. I get about 10 mins of flight time(mostly run it at 1/4 to 1/2 throttle, APC 12x4 prop).
Zach

ro347

My Feedback: (13)

It just hit me...i def think my low end is still rich. My idle is at 3200rpms. Ive never dealt with it as it worked fine, no pulling issues etc....so IM SURE there is some room there.

Dumping fuel out of the vent if not properly positioned makes alot of sense. If i remember correctly I placed a small piece of fuel tubing on the vent line so the outlet should be hitting the top of the tank, but not 100% sure as its been a while since I assembled it. Ill have to check that again.

If the above fails to show a change, then will change the plug back to #8.

I will get to making these changes next week as ill be taking a few days off. I report back with the findings.

Thank you all!

gunny11

My Feedback: (6)

Definetaly change out the Four stroke plug and put in the OS #8 plug and retune to this plug. Have two of these in a cessna 310 and fly it WOT pretty much the whole flight and get 10 minutes.

Gunny

Michel

Hi

I have a 55AX . Broke it in with two tanks on the bench , as recommended in the instructions . W/O throutle , openning the needle rich , and leanning it out
At present I have about 30 flights , turning a 12X6 prop , and will be changing props to a 12X7 or a 13X6 . I run mostly W/O and have a 14 oz tank . I run well past my timer and have plenty of fuel left over . A 14 minute flight , minimum , 1 oz / min , and I have fuel left over . Not one dead stick
I think this is one of OS,s best engines . From read the thread , I beleive , it,s jst a matter of prop and tunning . Sorry no RPM . never needed it . Don,t wish to brag , but my idle is very very low

Michel