jbarnes

I've been playing with gas engines for a year now. I have a couple of Fugi's and couple of Evo's and I always tune them for max RPM on the ground and then when I take off they seem to get rich. Is this a common occurance for gas motors. I land, lean out the motor and then its fine for the rest of its life. But, should a guy be leaning out the motor a little more on the ground before that first takeoff? All the instructions seem to indicate to make it rich instead of lean but I seem to find the opposite to be true. Maybe this is something unique to my altitude (6,000)?

Not a major issue just curious, figure you experts can explain it to me. Thanks, Jerry.

TLH101

My Feedback: (90)

You do the initial tune on the ground. Then after flying, you fine tune to make it run correctly in the air.

Flypaper 2

They tend to unload in the air causing them to essentially go rich or go into the 4 cycle stutter. If you put it into a steep climb it will tend to lean out. I set mine up so that when you put it into a long shallow decent it will go into the stutter but in level flight it will stay 2 stroking.

cuwaert

Hi, another possibility is air turbulance. These carbs are very sensitive to it. I know of a similar problem with a king 200cc in an extra. After closing the air intake at the lower cowl with some tape it ran well both in the air and on the ground.

Carlos G

Hi Jbarnes,

It could be a couple of things that happen to make a carb behave the way you've mentioned. Air flow around the carburetor will make a difference how the carb behaves. Usually they will go towards the rich side (but Not Always!). This could be because of a cowling that may be creating slight pressure changes around the carburetor causing it to go rich. If possible you want to try and have static air (neither positive or negative pressure) around the carburetor. It might just take a small air deflector plate mounted infront of the carb to do the trick.

The other thing that can be causing the engine to go rich is that there may be a governor in the carburetor. It works by resonating at a predetermined rpm and then it will allow extra fuel into the engine to limit the maximum rpm the engine can reach. A governor will drive a person nuts because the engine will run fine on the ground and no matter much needle tweaking or prop changes are done, once the engine hits the magical resonance number, the engine will go rich. The reason for the governor was to keep the chainsaw/weedwacker/concrete-cutter from overspeeding and self destruction.

I hope this helps with your engine questions.

Best Regards
Carlos G

tstotts

Like Carlos says try flying it without the cowling. If this doesn't work sounds like a regulator problem. the regulator is under the silver looking cover with 4 screws holding the cover on and a small hole in it. If you see any fuel leaking out of the little hole your regulator diaphram has been ruptured. slip off the cover and check the diaphram. Don't use a screwdriver or knife to remove the cover as you wil most likely wind up tearing a hole in the diaphram. use a small hammer and tap on the edge of the cover to dislodge it. If the diaphram is ruptured or stiff with old age replace it. hope this helps

Tired Old Man

My Feedback: (1)

You're probably tuning a cold engine at the beginning of the day. It didn't go rich, it just simply never reached it's optimum running temp. A VERY common mistake among newcomers to gassers. Let it warm up a bit before twisting the needles.

Other that the above, some engines have an issue with air impacting the diaphragm, causing unreliability at various attitudes and rpm levels. Takes a little time and experimenting but it can usually be worked out satisfactorily.

jbarnes

Thanks for all the comments. Once I get the needles dialed in the motors run fine for the remaining part of the season but I was of the opinion that the gassers could be adjusted on the ground and then they were good to go.

Flypaper 2

Don't worry about what it does on the ground. As said above, the pressures are different when it's flying. These carbes are designed for fixed industrial engines, chain saws, weed wackers, tampers,generators etc.

rmh

they can - once you learn which ground adjustment performs best in the air.
setting on th e ground at full throttle the engine is working it's hardest - as it moves forward the work load is less
here is a big secret
more work takes more gas - shhhhh don't tell anyone.
so depending on the work done - the engine will sound different.
It is working harder or more easily
because the carbs we use are fixed ratio devices - yo u have to compromise (just like being married)
if you make it run sparklin clean in level flight - the gas supply is not right for pulling hard going straight up from a hover. So adjust YOUR engine for the hard work it will do and if it bumbles a bit when the load is less - just tell the experts it "snorze" when it is resting.

captinjohn

How about the rotary barrel carb....seems like on a Echo leaf blower (big one) the engine runs pretty smooth at all RPM without burbling. Capt,n

rmh

thee load changes a lot at various rpm on the model airplanes

Tired Old Man

My Feedback: (1)

The rotary barrel Walbro brings about a new set of issues all it's own. The WYL carb is actually more of a pain to adjust than the butterfly type. I've been involved with them in my work for quite some time. Stay with the butterfly types for now.