R

riobison

Well Known Member
Carb leaning

It's like my engine is always running lean?

In leaning my RV4 w an 0360 and FP prop I'm not able to lean to peak power. I fly out of an air port at 3700 asl and when leaning to max power I'm not able to see on my digital tach the increase in rpm. Nor am I able to hear it. I will keep leaning to until it starts to miss and that part is normal . I took it up to 12,500 asl and pulling 2600 rpm (maximum) and tried to lean again for max power but again I could not see nor hear an increase in RPM to tell me I'm at max power. Instead I would lean until the engine would start to miss. I have left the fuel pump on, checked and cleaned the air filter and inspected everything that I can see externally and everything seems normal. I have 10 hrs on the plane and it has done this since I have had it.

Has anyone any ideas or suggestions on this?

I have adjusted my carb heat and now I can see about a 30 to 40 rpm drop with it on. Not like a Cessna but from what I have read this is normal for the RV's

When apply full power from an idle or go around it will always hesitate before going. This I think is because I don't have an accelerator pump so this is probably a different issue.

Otherwise the engine seems to run good and seems to get off the ground quick at 3700 asl, climbs over 1600 fpm at 2250 rpm and top end is 200 mph. Oil temp is normal. As far as EGT and Cyl head temp the gauges always seem to be on the low side so I don't put a lot of faith in them.
This leaning thing seems a little weird to me.

Thanks

Tim
 
The hesitation is normal on an O-360. Never saw a MA4-5 carb that didn't have a accelerator pump. But there is no external indication they have one all the parts and linkage are internal.
You say you have an egt gauge.... use it to determine the amount you are rich of peak egt rather than looking for a rise in RPM. If you see a rise of 75 degrees or more from full rich to peak egt, in cruise, at altitudes below 4500 feet the carb isn't all that lean. If you are seeing less than 50 degrees then it could be richer but still Ok in my book. Less than 25 degrees of leaning capability at 4500 asl is too lean and you should pursue it in my opinion.
EGT will give you an excellent indication of how rich or lean you are, by analyzing the spread from full rich to peak at any power setting.
Good Luck,
Mahlon
 
I put on 500 hrs in my Cardinal 177A with an 0360 and it never hesitated not even once but it had an accelerator pump. My RV4 has an 0360 A1A and there is no accelerator pump, at least no externally. I'm not sure of the carb model but I will pull that data next time the cowl is off.

This is my 1st experimental so some things are new to me and are specific to these aircraft due to their design differences. Most of them are good and some questionable but are acceptable.

I'm not a high time pilot but I do have over 700 hrs in a dozen different models from the big three and I could always hear and see an increase of 50 to 75 rpm when leaning for Max Power on the ground or in the air. This is the 1st plane that I have not been able to do that with. And at 12,500 ft I would really consider that abnormal.

On a side note it is hard to believe the performance out of this thing. Doing circuits and only burning 6 gap is unbelievable (my 7ECA burnt more than this) I was triple checking my numbers as it seemed so low. But being throttled back to stay with the flow of the traffic explains it.

I just completed my 1st 2 hr XC between 6500 and 8500 ft @ 2600 rpm while burning 8.75 gph and 200 mph TAS.

Thinking about it still excites me.
 
Can someone explain to me in simplistic step by step terms how to determine ROP, Peak and LOP using EGT i guess.
 
Ryan: slowly lean (slow so the gauge can catch up) and watch the EGT. It will go up, up, up, then go down, down, until the mixture gets so lean the engine stumbles and/or stops. Put the mixture control in the position where the EGT was a maximum, you are now at peak EGT. Go richer, you are rich of peak. Go leaner, you are lean of peak. Note some carb'ed engines may run rough before even getting to peak.

Tim, it sounds to me like your carb is too lean. There is an idle mixture adjustment screw. Usual ground test is to idle about 800 RPM, full rich. Suddenly pull the mixture to cut off. Just before the engine dies there should be a small, like 50, RPM increase. If none, you need to enrichen. If it's 100 it's too rich.
 
Hello Bob,

When shutting it off, it does not pickup any rpm what so ever. So I will en richen the idle circuit with that screw.

But with it being on the idle circuit, will that have much if any effect on the mid to top rpm where I spend most of my time and could be the most costly if it's not set up properly?

I'm competent in tuning Hi Perf 2 strokes like in snowmobiles but I'm not overly familiar with these carbs so I'm making some assumptions here that's all.

Thanks

Tim
 
The answer is yes. Although it is set at idle, it will affect the mixture thru the whole range of power.
Let us know how this works out.
 
Seems to me that a carb needs to be set up so that it is rich enough at the condition that requires the most fuel flow.

Wouldn't that be at sea level on a cold day?

I have an O-320-E2D, and the carb was too lean on the ground. I ended up drilling the jet, and: ...Much Better! Search for extensive threads on the pros and cons of drilling the jets out.

You can always lean the mixture, but you can't make it any richer if you are already at full rich. And if full rich is not enough, you are running too lean at high power settings at low altitude, such as during takeoff.

You might try leaning at fairly high power on the ground, and see if you can lean to a peak EGT. If not, then you are likely too lean at full rich on the mixture.

Hope this makes sense, and other more expert folks please chime in.
 
BobTurner said:
The answer is yes. Although it is set at idle, it will affect the mixture thru the whole range of power.
Let us know how this works out.
Click to expand...


Is this correct? I have always been under the assumption that just over idle, the idle mixture went out of the circuit and it ran on only the main jet. If that assumption is true;), then adjusting the idle mixture would have no effect on higher power settings.

I'd just like to know which is correct.
 
I only am familiar with the MA4-5 on my former 182. There, the idle jet was always on if the mixture control was forward. At higher throttle settings, you had both the idle jet and the main jet flowing fuel. Note the above referenced adjustment makes the idle mixture too rich (which is why you see the RPM rise during shut down, as the mixture momentarily is optimum). But supposedly that would make the full power mixture the correct amount of over-rich.

PS I agree with a previous post, this test should be done near sea level.
 
Idle circuit has absolutely nothing to do with mixture control. Idle circuit loses almost all effectiveness once the lip of the throttle plate moves away from the bleed hole in the venturi. A tapered pin is withdrawn from a orfice near full throttle to allow passage of "extra" fuel. This is called the power enrichment valve. If you fly at full-rich, WOT and cannot see a substantial EGT rise your carb is definitely out of whack.
 
If you fly at full-rich, WOT and cannot see a substantial EGT rise your carb is definitely out of whack.
Click to expand...

If you fly at full-rich, WOT and cannot see a substantial EGT rise WHEN LEANING your carb is definitely out of whack.

Brain to keyboard interference.
 
It shows maybe a 200 deg climb when leaning to roughness but it never goes over 1100 deg. It is hard to see exactly what I have as where the gauge is located at a bad viewing angle and with the seemingly low temps I don't have a lot of faith in it.

I tried again today with wide open throttle at 8000' asl and 2650 rpm. I tried to see an increase in RPM and I could not see anything. Nor could I hear anything as far as an increase in RPM. I pulled until rough and then en richen slowly and still no change even back to full rich.

I'm thinking the carb is slightly out of wack. With the ram air effect, K&N air filter and Vetterman Exhaust the engine is probably flowing better and could be making a little more power than stock because of this. We know the vast majority of the factory AC the air intake is so choked and these engines and carbs are set for those planes.

Putting them into the Vans that flow better could put them slightly out of calibration or running leaner than normal. Just my thoughts.

Lots of options but I will take the carb out and rebuild it to make sure nothing is plugged and if need be I may have to go one size bigger on the main if that is possible.

Or another option is find one with an accelerator pump to help take out the bog. Nothing I hate worse than over shooting a bad bounce I mean landing and having it hesitate for a second when I really need the power.

Tim
 
If you have a 200 degree EGT rise when leaning to peak, your carb is not to lean. Likely your tach isn't that responsive. If you are seeing the EGT go up 200 degrees, then you are getting an RPM rise but not seeing it.
1100 degree EGT at full power or cruise would indicate a rich mixture not a lean one assuming the probes are reading correctly and located within 2-4 inches of the exhaust port.
The idle mixture adjustment on an O-360 updraft carb will have no effect on the higher power mixture. The idle mixture on a horizontal draft carb model HA-6 will effect low cruise power. The idle tube in a MA4-5 carb which is what is used on the vertical draft O-360 delivers idle fuel through the idle tube and then at about 1200RPM the idle tube starts to transition to being the air bleed for the main discharge nozzle. When in transition, the carb very often produces a flat spot or hesitation in acceleration.
The flat spot produced can be of varying severity but it is almost always there if you look for it. Sometimes it is downright scary and sometimes it is an aggravation and sometimes it is only noticeable to a very fine tuned feel. But 95 percent of the time it is there.
To see if you have an accelerator pump or not, simply pump the throttle several times and see if fuel drips from the airbox. If you get fuel you have a functioning accelerator pump and if not it is either missing or inoperative. The accelerator pump on a MA4-5 carb will shoot a stream of fuel 10 feet when activated with the carb off the engine.
Good Luck,
Mahlon
 
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When I pull my carb heat on I do see an RPM drop of about 30 to 40 rpm. I'm thinking the tach is sensitive enough.

So I should see an increase when I lean it and I still don't.

There is no accelerator pump on this carb. The engine is an 0360 A1A
 
miyu1975 said:
Can someone explain to me in simplistic step by step terms how to determine ROP, Peak and LOP using EGT i guess.
Click to expand...
Ryan:

You cannot go LOP on a carborated engine. If you try to and if you have a digital Tack and EGT you will notice that your RPM will drop. If it drops so does your PEAK point so you are never running LOP.

As for ROP - Easy...
And you can cross check your self with an EGT but! It is amazing how accurate your ears, hands and feet are...
Get to altitude. And slowly pull out the mixture until you HEAR & FEEL the engine stumble. Then richen up two turns or one click in. You are there.. Don't believe me? Cross check against the EGT. You will see the EGT peak and then when you richen up it will drop about 50 Deg F. BINGO you are there. That simple.

Barry
 
Barry_Barry said:
Ryan:

You cannot go LOP on a carborated engine. If you try to and if you have a digital Tack and EGT you will notice that your RPM will drop. If it drops so does your PEAK point so you are never running LOP.
Barry
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Barry,

I can sort of see the point you are making but what about a carb engine with a constant speed prop? Also why can a FI engine go LOP but a carb engine that happens to have even fuel/air distribution between the cylinders can not - what's the difference?? And lastly electronic ignition often allows a carb engine to be leaned past peak into what most people believe is LOP.

Fin
9A
 
Barry
You cannot go LOP on a carborated engine. If you try to and if you have a digital Tack and EGT you will notice that your RPM will drop. If it drops so does your PEAK point so you are never running LOP.

As for ROP - Easy...
And you can cross check your self with an EGT but! It is amazing how accurate your ears, hands and feet are...
Get to altitude. And slowly pull out the mixture until you HEAR & FEEL the engine stumble. Then richen up two turns or one click in. You are there.. Don't believe me? Cross check against the EGT. You will see the EGT peak and then when you richen up it will drop about 50 Deg F. BINGO you are there. That simple.

Barry
Click to expand...

It must be just me and my personality, very friendly, help out far too many people and yet when I see a post like this I want to reach down the computer screen and strangle the author for posting such garbage.

So please, understand that I am not picking on you, being a bully or any of that other stuff............ but your post is full of CHARLIE RAP.

Have you ever considered what happens when you fly an O-360 with a constant speed prop?

I can assure you, and with data backed from not just my own flying with many carby setups belonging to friends who have them, both fixed and CSU, that this is possible if you have a conforming engine and know what you are looking at.

Heck, if you dont believe me, take on George Braly in a debate on the matter, when you lose, come back and tell us what you learned! ;)

So back to the facts, once you get past peak EGT or where it would have otherwise been with a FP prop, fuel flow is what determines power, not MP or RPM.

I know what you are experiencing, when you hit peak RPM you are at 70-80 ROP, the curve is pretty flat for a while heading to peak EGT but the HP and CHT start falling. by the time the RPM really drops you are on the lean side anyway. The delta T in EGT is too great to be just RPM affect alone.

I challenge anyone from VAF to turn up at the next APS course in Ada OK in October, wear your VAF shirt, and say you flew in to the weekend in your RV. I think I am the only RV owner who has ever been there, but from Australia I had to use a Boeing! Anyway you will be a first!

Finley
Just a caution on your beliefs there, it all depends! If the electronic ignition is advancing the timing, when it does the EGT drops anyway. This is part of the problem when you have an EI and a magneto. The EI fires first, the magneto does nothing much, makes a good backup but that is all. Two EI's working together however are possibly better but as timing changes so does EGT and CHT and its harder to fault find with a variable.

So back to Barry, do you think 50 ROP is a great way to operate at all power settings?

It certainly is not, and today I was by phone coaching a pilot of an RV7 at FL155 about using 70-80 ROP which was quite OK, and 10 LOP which improved MPG a lot, but at no time did 50 prove to be beneficial, it was neither fast nor efficient. In no mans land. At high HP levels, this would be not good, but using your stumble method you could find that happens at 60-30 LOP at high powers (still not good) but definately LOP.

You should never quote a cookbook answer that applies to one scenario and not all others. There is more to it than that. This is why so many Lyc and TCM manuals are so full of contradictions and errors .....yet approved, by the FAA no less!
 
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Found the problem

My AME found my problem but it took us a good hour of messing around. The mixture lever was hitting the clevis before it could hit the stop on the carb. In short, there was about 1/8"+ gap between the lever and the carb so I was never getting full rich like I thought. We ground out a little on the lever so it would have clearance to swing into the clevis and give me full stroke. The plugs were very clean and almost too lean. It appears that this plane has always been like this for 500 hrs and no one else had realized there was a problem. Good thing most of the flying has been around here at the higher elevations and not down at sea level on a colder day.

With it being lean was also causing it to hesitate when advancing the throttle on a go around and that is now gone now that I have full rich.

Everything is back to normal.

Life is good.

Tim
 
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