i just finished my first plane(SIG SENIOR)from a kit.got the motor in,dragged it outside on the picnic table and ran two more tanks thru it(4 total).the motor is an GMS .47 and i'm running omega 10% thru it with a 11x7 prop.
HERE'S THE PROBLEM!!
i can get it to idle nice but i can't get it to go to full throttle.somewhere around half gas she quits on me. she does it when i throttle up slow or fast! very confusing for a newbe!!! i leaned out high speed mix to one full turn from bottoming out.instructions tell me to bottom it out then back it out one and a half turns as a good starting point. is it possible that it still needs to be leaned out some more?? ANT INFO WOULD BE HELPFUL!!!!!!!!!! IN PROSSES PICS!!!

Bring it to the highest rpm it will run without quiting. Then pinch the fuel line going to the carb.

If the rpm's speed up its to rich and you need to lean it. If it quits immediately its too lean.

Bring it to the highest rpm it will run without quiting. Then pinch the fuel line going to the carb.

If the rpm's speed up its too rich and you need to lean it. If it quits immediately its too lean.


Oops, didn't mean to post twice...[X(]

Follow Wings advise. That will fixer up....

Could be two problems.
Does the rpm drop down when you remove the ni-starter ? (Needs a new plug.)
Try opening the main needle 2 turns from close and once you open full throttle (while someone holds the plane) start leaning till you get max rpm, then richen 2 or 3 clicks.

why start from 2 turns out?

You may have to start from 3 turns out. It may be too lean at high end to start with. That's why Wings suggestion should work. Read it carefully, if you run the motor up to max rpm (not neccesarily full throttle) and run the pinch test, if it dies right away, it is too lean, and you will need to rich it up. Once you do it a few times, you will get the hang of the system...

It is confusing at first. Did I get from your original post that you are opening the needle valve to lean it? As you open the valve, you are richening the mixture.

big-bird. Not to point out the obvious, but from the pictures I don't believe you're quite finished! I don't think that dog's ready to hunt just yet.......maybe a little more covering on the fuse and wings????

Unless at your present setting the exhaust isn't blowing a lot of oil and unburned fuel, it's too lean. That's why you need to open a little more so that you can at least get max throttle to adjust for near max rpm. Does it burble stutter and die or just dies suddenly ? If suddenly, it's too lean. The forementioned pinch test will tell also. What about the glow plug ?
We'll save the low end needle for another thread.

i'm closing the needle valve then backing it out 1 1/2 turns to start.i've closed it 1/2 turn so far(turned it to the right(clockwise)).when i took the ni-starter off the glow plug i did not noticed any drop in rpm or sound.next time i'll try starting at 2 full turns out then try to tune it.

i just wanna say thanks for all your help guys but i got one more question.will a royal .46 power a us aircore trainer? i wanna use this trainer first to learn on! i put way too much time,blood,sweat and tears into my SIG KADET SENIOR to see it in a pile of sticks!!!!!!( a good way to see a 35 year old cry!!)

those are old pics. she's fully covered!! and beautiful!!!

I have found an 11 x 7 prop a little much for an engine in that size range. I have gotten better performance with an 11 x 6. When you get the engine running well try the 6.

46 will be fine on the Air Core.
Don't be worried about too little aileron movement ( 3/8"up or down) on the AirCore. I've helped students on that plane and it's more than enough to bank it.

thanks rreiss!!!

bybird, a .46 is fine for a Aircore trainer. I flew mine with both a .40 and .46. The larger engine was much better.

Sounds to me like your top end is still too lean. I'd start with the main needle 3 turns open at least, if it still won't go full throttle then I'd look for an obstruction in the fuel line or presure line to tank. You really can't open the main needle too much when first breaking in an engine, just run it up rich then lean from there. The settings given in the manual are suggestions, you gotta go with what works.

Andy

I find most transiotion problems are low end related. The engine runs on the low speed needle for about 2/3rds of the time. Only the last 1/3 is high speed needle. If no amount of high speed needle tweaking gets you there. And your glow plug is good. And you check for no air leaks around the carb base and the engine backplate. Try adjusting the low end needle. Any of the above can give you fits trying to get a good transition. One last question, is your fuel fresh? This also can cause fits. Good luck with it.

And to answer the Royal question, Absolutely! The older Royals were a decent and fairly powerful engine. Good luck with it.

Mark Shuman

hey phread59,first let me say thanks! second,how does one check for air leaks around the carb base and the engine backplate?you also said" Try adjusting the low end needle." does it adjust like the high speed needle? will the pinch test work at low speed also?

The pinch test is simple and easy. You've already monkeyed with the high speed needle so its not like you are going to screw it up.

What WILL give you fits if you screw around with the low end. I personally find this more difficult to fine tune. I would do the pinch test first before I touched the low speed.

Just my humble opinion.


Wings

I agree with phread59. Since you have the high speed needle well backed out I suspect that the problem is low-speed needle related, & I also suspect that it is too rich. When you do the pinch test and determine whether it is rich or lean, adjust the LOW speedle needle in 1/8 turn increments & test again. Another diagnostic test that has already been mentioned is monitoring HOW it quits when you open the throttle -- if it sputters & stumbles, the low speed needle is too rich, if it quits dead the low speed needle is too lean. When you are able to actually get the engine to run at full throttle, peak it then go back to idle & start the tuning process all over again. The needle settings are somewhat interactive & you need to have them both "in sync" for best performance.

Sound like you need to enrich the low end needle valve which is the screw inside the throttle arm,turn it out about 1/2 turn and try that.
I have the GMS .47 and it's a VERY good engine, NO problems here.

I'm no engine expert by any means but someone gave me this tip......

Low Needle Pinch Test (for adjusting low end needle)

Run full throttle 15 seconds
Run Idle throttle 15 seconds
Pinch line to carb:
if it runs, then speeds up until it dies, its too rich
if it dies, too lean
if it runs and then dies with little rpm change, its good


Dave...