STG

My Feedback: (26)

In a down line with motor in high idle (about 2,300 on the ground) my motor goes quiet (like it is not firing?) as RPM increases & engine is being turned over against compression by the prop(Down line breaking). I was a bit concerned that the motor was going to quit and about 10 down lines later it did.

I am trying to understand what is happening with fuel mixture on a walbro carb when this wind milling happens at a low idle setting. Could this cause the mixture to go too lean and & motor to quit?

nmking09

My Feedback: (61)

I would check the compression, sounds like you have a leak somewhere.

STG

My Feedback: (26)

The motor is a Brillelli 46 and compression feels good. The motor is performing well in all other aspects.

altavillan

My Feedback: (1)

2300 rpm on the ground is an extremly high idle setting. It would probably be running around 4500 if the prop was not there to slow it down. So when you point the nose down and the plane speed catches up to the prop speed you have little braking going on. That rpm also puts it in the dreaded midrange burble. No load on the engine yet getting all the fuel as if there was a load. No heat to keep it running either.

Recomend you set your needles for a low idle of about 1200 rpm and be able to idle for 5 minutes on the ground. Set your transmiter to kick up the idle rpms to about 1800 when flying. If it will not idle 1200 rpm then it might be too low on compression, timing might be off, rings might be stuck, reed block might be bad or wrong carb or carb needs rebuild. Few 50cc and smaller carbs have diaphram issues, they do not have a forked nipple.

altavillan

My Feedback: (1)

Ah... I finaly got my hands on a echo 4500 saw and converted one of those engines. Sweet! Mines in a giant UDO no cowl absolutely no airflow issues.
Has to be a carb setting thing.

STG

My Feedback: (26)

Low idle is ~1,700. I don't think it is reliable below that--Maybe I need to look at this harder. I have been flying on the high idle setting(~2,300) and clicking to low idle(~1,700) if I don't have a head wind to land into. Down line braking seems to be very good with a Xoar 20x8 prop at the high idle position.

Even if the prop speeds up to 4,500 in the down line from wind milling, I do not think the carb meters as it would under load because the butterfly is in a near closed idle position. [&:] It sounds like you think it is actually going rich?[&:]

altavillan

My Feedback: (1)

Yes I would say it's too ritch. Try going in an 1/8 of a turn on the low side. Then see if the idle is lower. Keep resetting it till you get the idle down a ways. Then keep experimenting till you get near 1200 or lower. If you get a good low idle then do the high side. Adjust it pretty much like a glow engine. Peek rpm then back off a little. You have to fine tune after a flight. You want just a little burbling on strait and level and a good 2 cycle when pulling hard. It takes me 5 to 20 flights to get one right, and they will need adjusting occasionaly

STG

My Feedback: (26)

on this carb, 1/8 on the low side will make it too lean on the ground.[&:]

I am trying to figure out how the motor is getting too much gas with the butterfly in the closed postion(idle) and the motor wind milling? [&:]

It is true though that I don't have much burbling on the the strait and level [&:]

rmh

your pictures shows why it goes rich - on most Walbros--with throttle blade closed --the low speed discharge is seeing very high vacuum.
some carbs run a tiny bleed hole in the throttle plate to prevent this enrichining- some run a tiny slit in edge of throttle blade .
same reason -

the picture is incomplete --among other things ---- the hole on one side of the throttle plate (left) --is from low speed needle --the two on other side -(right) high speed needle (which is not shown)

altavillan

My Feedback: (1)

STG; 2300 rpm is not an idle . It's 1/3 of your available rpms. However if you can't get it to idle reliably lower than that there probably is something wrong with the carb. Send it back or take it to a saw shop and have them try to adjust it.

RTK

My Feedback: (1)

Dick, maybe I am seeing something wrong, but I see (3) holes on the low speed circuit and (1) on the high with a needle.

Tired Old Man

My Feedback: (1)

If the engine will not idle low enough for the plane to sit still without being held then the carb is either incorrectly tuned or defective. 2,300 is outrageously high for that size engine. First thing if it was mine would be to set both needles back to a base of 1-1/2 open and start re-tuning.

STG

My Feedback: (26)

I should have listed my source for the picture: http://www.wind-drifter.com/technica...viceManual.pdf
I did not know if the picture is correct & I do not fully understand the workings of these carbs. Thanks for the help.

STG

My Feedback: (26)

My field is rough & I need full up elevator on the ground to keep the tail down. @2,300(high idle for flying) it is just moving with a Xoar 20x8 prop @1,700 it is not even close to moving (on rough grass field) and it will idle there reliably--might even idle down to 1,500, but I did see any reason to push it.

I guess I should spend more time trying to adjust my low speed at lower idle settings. I know many with this motor have noted that they cannot kill the motor by closing the butterfly at low idle--thus far if I have tried anything below 1,500 for extended periods the motor would quit.

I find my low and high-speed needles very sensitive to any change. This Walbro carb may be different from most because starting H speed needle is 4-3/4 and L speed is 1-3/4. I hate to adjust anything from where it is at because the motor responds so well as adjusted.

So you guys set your low idle around 1,200 and your high idle for flying around 1,700? I am pretty green on this stuff so have a lot of stupid questions.[&:] I appreciate all the help from you guys.

STG

My Feedback: (26)

I found this artical By Branwell: http://www.geistware.com/rcmodeling/glowpower/gas.htm

I don't know if this info is correct, but he says " You might have to richen the low end to.... insure good down line breaking, but remember to keep the bottom end as lean as is practical, this will help insure a good midrange response. "

Why would he be saying this if wind milling creates a rich condition?

I understand how frustrating it is to give your time to help someone and then have him or her seem to not believe what you say. I am only trying to pump those more knowledgeable than me for information so I can get a better understanding on the Wabro carb. Again thanks all for the help.

rmh

I only glanced at the drawing -oops-
but ---- a high vacuum does exists on the engine side of the throttle plate -when the plate is closed .
as the plate gradually swings back over the other low speed holes (if there are anymore -some do - some don't) more fuel flows (depending on the needle opening- and depending on the engine -- the transition is better .
. (is that better? )
some engines will not shut off because there is no back pressure in the exhaust --typical of engine with NO muffler .
as for 4.1/2 turns open-- never seen that adjustment setting usually as you go over 2.5 turns you are wide open.-

STG

My Feedback: (26)

I found this to be interesting reading on the Walbro carb--I know this is not new for a lot of you.

http://www.drystacked.com/Walbro%20C...y%20ebook1.pdf

Scott Ellingson

My Feedback: (146)

The WT 349 carb has a very fine thread needle on the H side and does require more turns than the avarage 1 1/2. Walbro has many carbs like that.

I have also found being too lean on the low will cause a higher idle. If it is too lean it just will not idle low without shutting off. I have richened them up a hair in those cases and achieved a far lower reliable idle.

altavillan

My Feedback: (1)

STG By good downline breaking he means, you do not want the engine stumbling as you add power at the end of a down line. If you go too lean on the idle needle the engine will hesitate, and possibly cough and die when you accelerate rapidly. All fine settings have to be peformed after a flight to see what or where you have to adjust.
Dont worry my plan is for your patience to run out before mine

STG

My Feedback: (26)

[sm=lol.gif][sm=lol.gif] Though I do want the help from experts, it is hard for me to just follow what they say-- it takes me a while to digest and understand.

If the motor has low speed set well for all other flying and in a down line the motor windmills causing a bit richer mixture (than normal idle) than why would it stumble too lean at the end of a down line? [&:]

karolh

[quote]ORIGINAL: STG

I found this article By Branwell: http://www.geistware.com/rcmodeling/glowpower/gas.htm

Is this really the correct way to set the high end...no drop in RPM ??

karol

STG

My Feedback: (26)

I am no expert, but I did not agree 100% with anything I have read in any one article.

Depending on your flying style and set up here are some things that would allow you to set closer to peak--
1) Very good cooling
2) You don't fly at high or full throttle for very long
3) Sure it will not lean out any more in the air
4) Unturned motor that puts out less power and heat for its size
5) Very good oil and generous oil ratio

I think it best to set it back 100-200 or so from peak--again depends on your set up and flying style

karolh

That's pretty much my thinking and way of doing it.

Karol

Bob Pastorello

My Feedback: (198)

As Scott says - a LEAN low end end is not the road to happiness. Believe us. The too-lean-low end engine will idle remarkably-smoothly, but WAY too fast, and likely will not shutoff no matter what. That principle applies to many different engines, many different sizes.

The other main issue of too lean low end is hesitation in flight on throttle up from sustained low-throttle. Like exiting a spin. Or a Flat spin. Or at the bottom of a stall turn. All places where it is NOT a "good thing" to have any hesitation.

Richen it. Trust us.

RTK

My Feedback: (1)

I always set my low end as lean as possible, but not to the point where it will hesitate when the throttle is goosed/stabbed from idle (on the ground or in the air). It helps keep the lower mid range from running to rich when the high is set correctly. I have not yet owned an engine that could not be shut down by completely closing the throttle.
Being to rich on the other hand has almost cost me, I don't want the engine to have too clear it's throat for a couple of seconds.