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O-320 Help!

8213C

Member
I am having issues with my EGTs on my O-320 . My mechanic looked it over and concluded that I needed to have the carb replaced. So I did, flew, and this was the result. I could never get #3 cylinder to go under 1500 degrees even in cruise at full rich and, 2400rpm. My temps are, #1 1380, #2 1260 #3 1510, #4 1378 full rich. On takeoff on the ground it wouldn't rev past 2200 rpm, where it use to be 2350 with the old carb. She seemed super gutless in climb out and takeoff roll. In the climb out now, I saw 1605 and 1590 on #3 and #4. I'd have to throttle down to 2200-2300 rpm to get #3 into the 1470s in cruise at full rich; she feels real rough overall and more so on the left mag. I tried different power n mix settings for about 20 minutes but no change, just higher EGTs. I had the mags sent off and one was rebuilt right before all this at the time of the new carb install. Twice now I have been told she runs great, and the mechanic has released it like this. On the 1st test flight attempt, it was backfiring bad on run up with one mag dropping 500, so I didn't even fly it. They then cleaned the brand-new plugs which have barley 50hrs on them and richened it some. I don?t understand why the plugs would be fouled already since I always lean on the ground and always lean out for cruise but anyway no bad mag check or misfiring with mags dropping 100 on both L & R. Now still the EGT issue. They are higher temps then I had before and a greater spread between hottest and coldest. The other thing is my highest temp cylinder before the carb was #4 at about around 1500. Also, when I kill it now, it has a slow drop and no rise at all.

My compression is mid 70s and had no metal in the oil. The engine has about 800hrs SMOH. At this time, I had the 4-cylinder EGT gauge installed and I realized it was too hot and was told to change the old carb out for a new one would solve that issue. I have flown it 55hrs since the annual and now decided to go for it and replace the carb in effort to help those EGTs. I feel like I should have just left it alone at this point.

My mechanic seems to not be sure what to do right now.
Do I just need someone who knows how to tune this thing or any other advice out there?
Why would #2 be so much colder?
Why is just once cylinder so hot?
Why the lower RPM on the ground after being richened up?


:confused:
 
I’ve had similar problems recently on 2 different O-320’s I’ve built, just don’t have enough leaning authority. If you have a fuel flow it might be helpful to post those numbers. In my case both engines had to have their carburetors modified to get enough fuel flow with one going through multiple carbs. Having dyno’d several 320’s I can tell you carbs with the same model # flow differing amounts of fuel right out of the box. It seems the new “billet” carb bodies flow different than the traditional cast bodies, with the cast ones generally flowing more fuel. This seems to be happening more and more with the new stuff. I’ve heard fuel formulation is part of the problem as well. Bottom line-you need more fuel and will have to have the carb modified by a shop familiar with the problem. I’ve read posts hear where individuals have had success drilling out the main jets on the MA-4 SPA’s themselves.
When doing some carburetor swapping on the the dyno I found the -5217 to work better than some of the others.
I feel your pain ��!
 
EGT reading can be very confusing. Most have found that the position the probe is installed into the exhaust and its distance from the cylinder head will make a huge difference in EGT values. The exhaust cools very rapidly as it exits the engine. Most are installed about 2 inches from the flange and usually in a position that makes it easy to get to other stuff. More importantly to your issue is that they are all the same dimen from the flange.

See where that #3 is installed relative to the others ( distance from the flange) and if it is aligned any way differently. Or have damaged wire or even a bad connection back on the firewall where they are probably plugged into the harness. EGTs are a thermocouple and operate on a very minute voltage difference between two different metals in the probe and are very sensitive to resistance.

Also look up the 0-320 -XXX model number certifications and see which carb it should get . There is a mile long list of dash numbers which usually indicate jet orfice size ranging from 150 to 160 HP. Be sure you 've got the Correct carb dash number.

Another thought would be to swap the #3 EGT with another cylinder to see how it reacts.

Best of luck
 
I?ve had similar problems recently on 2 different O-320?s I?ve built, just don?t have enough leaning authority. If you have a fuel flow it might be helpful to post those numbers. In my case both engines had to have their carburetors modified to get enough fuel flow with one going through multiple carbs. Having dyno?d several 320?s I can tell you carbs with the same model # flow differing amounts of fuel right out of the box. It seems the new ?billet? carb bodies flow different than the traditional cast bodies, with the cast ones generally flowing more fuel. This seems to be happening more and more with the new stuff. I?ve heard fuel formulation is part of the problem as well. Bottom line-you need more fuel and will have to have the carb modified by a shop familiar with the problem. I?ve read posts hear where individuals have had success drilling out the main jets on the MA-4 SPA?s themselves.
When doing some carburetor swapping on the the dyno I found the -5217 to work better than some of the others.
I feel your pain ��!


Thanks for the info. Its been super frustrating, im going to relay this to my mechanic.
 
I am having issues with my EGTs on my O-320 . My mechanic looked it over and concluded that I needed to have the carb replaced. So I did, flew, and this was the result. I could never get #3 cylinder to go under 1500 degrees even in cruise at full rich and, 2400rpm. My temps are, #1 1380, #2 1260 #3 1510, #4 1378 full rich. On takeoff on the ground it wouldn't rev past 2200 rpm, where it use to be 2350 with the old carb. She seemed super gutless in climb out and takeoff roll. In the climb out now, I saw 1605 and 1590 on #3 and #4. I'd have to throttle down to 2200-2300 rpm to get #3 into the 1470s in cruise at full rich; she feels real rough overall and more so on the left mag. I tried different power n mix settings for about 20 minutes but no change, just higher EGTs. I had the mags sent off and one was rebuilt right before all this at the time of the new carb install. Twice now I have been told she runs great, and the mechanic has released it like this. On the 1st test flight attempt, it was backfiring bad on run up with one mag dropping 500, so I didn't even fly it. They then cleaned the brand-new plugs which have barley 50hrs on them and richened it some. I don’t understand why the plugs would be fouled already since I always lean on the ground and always lean out for cruise but anyway no bad mag check or misfiring with mags dropping 100 on both L & R. Now still the EGT issue. They are higher temps then I had before and a greater spread between hottest and coldest. The other thing is my highest temp cylinder before the carb was #4 at about around 1500. Also, when I kill it now, it has a slow drop and no rise at all.

My compression is mid 70s and had no metal in the oil. The engine has about 800hrs SMOH. At this time, I had the 4-cylinder EGT gauge installed and I realized it was too hot and was told to change the old carb out for a new one would solve that issue. I have flown it 55hrs since the annual and now decided to go for it and replace the carb in effort to help those EGTs. I feel like I should have just left it alone at this point.

My mechanic seems to not be sure what to do right now.
Do I just need someone who knows how to tune this thing or any other advice out there?
Why would #2 be so much colder?
Why is just once cylinder so hot?
Why the lower RPM on the ground after being richened up?


:confused:

I would tend to think this was originally an ignition issue, and has been complicated by incorrect solutions. Poor ignition will slow burning and as a result will increase EGTs because the air/fuel mixture is still burning while exiting the exhaust. You can see this when you drop to one mag on a run-up...EGTs will rise and CHT will drop. The fact that EGTs are different from one cylinder to another is a little misleading and not necessarily bad, EGTs are not to be diagnosed like CHTs.

The fact you had a mag rebuilt and you were obviously having ignition problems at the same time tells me there's something wrong with that mag or that side of the ignition system.

Read this Mike Busch ARTICLE and then do a mag check.

Do a run-up in accordance with Lycoming SI 1132B. Make sure the RPM drops are within said limits, and note the EGTs and CHTS during the mag check. This will give you a good idea how your ignition system is running and possibly narrow down the problem.

If the run-up is good and you feel OK flying, then do an in-flight ignition check after leaning for cruise. This may give you more information regarding the health of you ignition.
 
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EGT reading can be very confusing. Most have found that the position the probe is installed into the exhaust and its distance from the cylinder head will make a huge difference in EGT values. The exhaust cools very rapidly as it exits the engine. Most are installed about 2 inches from the flange and usually in a position that makes it easy to get to other stuff. More importantly to your issue is that they are all the same dimen from the flange.

See where that #3 is installed relative to the others ( distance from the flange) and if it is aligned any way differently. Or have damaged wire or even a bad connection back on the firewall where they are probably plugged into the harness. EGTs are a thermocouple and operate on a very minute voltage difference between two different metals in the probe and are very sensitive to resistance.

Also look up the 0-320 -XXX model number certifications and see which carb it should get . There is a mile long list of dash numbers which usually indicate jet orfice size ranging from 150 to 160 HP. Be sure you 've got the Correct carb dash number.

Another thought would be to swap the #3 EGT with another cylinder to see how it reacts.

Best of luck

Thanks for the input. Prior to the new carb the #3 cylinder was running 1390 in cruise configuration. The prop shouldn't have been messed with when the new carb went on. Ill have to try to move them and see what reading i get. My mechanic claimed he matched the serial #of the old carb to the new one, but could be the old was modified and we dont know it.
 
if you decide to richen the jet

do it with a reamer instead of a drill bit. Works better.
And, a little at a time...careful to not overdo it. dismounting and remounting the carb is a pain and may take several tries. Also, be sure your jet is the aerated type.
.003 is actually a lot more fuel flow.
Ron
 
Also...look for induction leaks on the hot cylinder which could cause a leaner mixture. Lean in flight and see when that cylinder peaks compared to the others. They can certainly be off compared to the others because you don't have the fuel balance of fuel injection, but if it's running lean because of an induction leak it will peak much sooner than the other jugs.

What are your CHT's doing?
 
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Thanks for the input. Prior to the new carb the #3 cylinder was running 1390 in cruise configuration. The prop shouldn't have been messed with when the new carb went on. Ill have to try to move them and see what reading i get. My mechanic claimed he matched the serial #of the old carb to the new one, but could be the old was modified and we dont know it.

So one of the problems with messing with the carb jet sizes is that you can?t really match it by carb p/n. The engine and prop combo determine the proper carb p/ n. If you have a constant speed prop vs a fixed pitch, it can change the jet requirements. When you drill or ream out a jet, you fix your problem, but create a new carb configuration, that you can?t buy or possibly get overhauled without what you get back being different. There are several p/ns of carbs that are the same except for jetting.
That said, total fuel flow can be used to see if the jetting is off.
 
Also...look for induction leaks on the hot cylinder which could cause a leaner mixture. Lean in flight and see when that cylinder peaks compared to the others. They can certainly be off compared to the others because you don't have the fuel balance of fuel injection, but if it's running lean because of an induction leak it will peak much sooner than the other jugs.

What are your CHT's doing?

Cool, Ill give that a shot. I dont have any means of measuring my CHTs so I dont know.
 
Induction leaks are worst at idle when the difference between barometric pressure and manifold pressure is greatest. If your idle is not substantially affected you are not likely to have an intake leak.
 
There's more to carbs than just carbs...

My RV-9A had really high EGT on one cylinder when I got it. I called Marvel-Schebler to find out what to do about it and asked about enlarging the jet. NO! NO! or something like that...

I traded my carb for a MA-4SPA 10-3678-32. The significant part of the number is that part past "MA-4SPA 10," which by itself is an incomplete specification. The rest of the number, in my case, meant that my carb ran richer than other models. And, mine was bench calibrated at the rich end of the scale.

Call 'em up (if that's who made your carb.) They gave me excellent tech support and kept me from wasting time and screwing things up.
 
In the climb out now, I saw 1605 and 1590 on #3 and #4. I'd have to throttle down to 2200-2300 rpm to get #3 into the 1470s in cruise at full rich; she feels real rough overall and more so on the left mag.

Sounds like ignition issue. When one plug stops firing in a cyl, the timing is retarded, which causes EGT to rise and CHT to drop. It will also create a small to moderate performance loss and slight roughness. The mag drop tells the story. When you drop the mag that is not driving the bad plug/wire, you will be running on three cylinders and she gets rough. Dropping the other mag will be noticably less rough, as it is running on 4 cyl. Watch the EGT during the mag drop to see if you have a bad wire/plug. EGT falls like a rock if there is no spark in a cyl for the single, selected mag. Don't be afraid to do mag drops at cruise power. Some ignition issues (bad coils especially) will not appear at lower power settings like a runup.

Each engine is different of course, but 1600 seem a bit high for a mixture issue. If you see an EGT that is higher than the "known" peak EGT for that cylinder, the cause is not mixture related.

Larry
 
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Check plug wire

If the EGT in #3 rises faster than the other EGT's it can indicate ignition issues. Possibly only one plug firing and excess fuel is burning in exhaust near the sensor raising EGT temp and this condition causes rough engine. You mentioned checking plugs and mags, but not plug wires(unless I missed it). Could have bad plug wire.
 
If the EGT in #3 rises faster than the other EGT's it can indicate ignition issues. Possibly only one plug firing and excess fuel is burning in exhaust near the sensor raising EGT temp and this condition causes rough engine. You mentioned checking plugs and mags, but not plug wires(unless I missed it). Could have bad plug wire.

The plug wires where tested and checked fine. I did an inflight lean mag check at cruise power yesterday. Had a drop of 100 and 110 rpm and minor roughness. I also ran it with carb heat and seen an increase in temps on 3 cylinders but that hot #3 drastically declined in temp. About 70 degrees

When finding peak egt. #2 cylinder peaked at only 1350 degrees. Which seems strange to me and #3 peaked very early @1620 and actually fell 150 degrees when finding all other cylinders peak
 
Hot egt

Maybe this was covered already and I missed it But I would check those spark plugs- remove them; clean them; gap them make sure that number three spark plug resistance is within range and not broken or cracked.
Also redo the mag synch make sure it?s at the 25 or whatever the 320 is for TDC and both hit at the same time.
Calling carb TS is a great suggestion, they will know how your carb was set and what to do to get it corrected.
I feel your pain, for years I fought CHT issues but in time, I got it resolved, and so will you.
Best of success with your troubleshooting
 
Exhaust Valve?

Has the exhaust valve on #3 been checked to see if it is sticking or not seating?
 
Ign

I'd place my bets on ignition issue also. You mentioned fouled plugs which is meaning that plug is probably not firing but being dosed in fuel. The problem is real as you mention weak takeoff and climb power.

EGT is a tough problem to solve because the number doesn't really mean much. These EGT wires going to the engine monitor can also be very sensitive. I had one wire with a very minor pinch and it made the EGT number decrease by 400 deg.

You need to start by making sure the sensors are giving you valid data. Remember these probs can vary a lot based on position and they're giving you a value (to 1 deg accuracy which is useless) based on exhaust valve open 25% of the engine cycle. What you really care about is are they reasonable close to each other and how they react to leaning.
 
Also check the inlet manifold gasket

I have seen a case where #3 had a high EGT. In the end it was broken inlet manifold gasket. Hard to see.
 
Has the exhaust valve on #3 been checked to see if it is sticking or not seating?

+1

If the EGT on #3 didn't fall off during the high power mag check, that takes ignition off the table. If all other cylinders are peaking around 1400, it is still not mixture. An exhaust valve that is either not fully closing (typically due to the common oxidizd oil build up in the valve guide seen on lyc) or a cracked or bent valve will cause higher EGT readings. When the exhaust valve doesn't fully close, the probe sees more consistent heat (both the power cycle and exh cycle, not just the exhaust cycle) and therefore a higher reading.

checking sensors is prudent, but they typically fail reading low, not high.

Larry
 
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The plug wires where tested and checked fine. I did an inflight lean mag check at cruise power yesterday. Had a drop of 100 and 110 rpm and minor roughness. I also ran it with carb heat and seen an increase in temps on 3 cylinders but that hot #3 drastically declined in temp. About 70 degrees

When finding peak egt. #2 cylinder peaked at only 1350 degrees. Which seems strange to me and #3 peaked very early @1620 and actually fell 150 degrees when finding all other cylinders peak

Looks like ignition is ruled out as the cause of the #3 EGT, since your ignition checks are coming out good and the one EGT is still high then that's doesn't seem to be the issue.

When you got the results with carb heat application were you lean of peak EGT on all cylinders? Carb heat should enrich the mixture because the air is less dense.

1. Compression and borescope to see how that exhaust valve is seating.
2. Look for induction leaks...start with a quick check of fuel staining like this http://airplaneownermaintenance.com/wp-content/uploads/2017/12/IMG_7372.jpg
3. Swap EGT probs between cylinders to see if the indication follows the swap.
 
Looks like ignition is ruled out as the cause of the #3 EGT, since your ignition checks are coming out good and the one EGT is still high then that's doesn't seem to be the issue.

When you got the results with carb heat application were you lean of peak EGT on all cylinders? Carb heat should enrich the mixture because the air is less dense.

1. Compression and borescope to see how that exhaust valve is seating.
2. Look for induction leaks...start with a quick check of fuel staining like this http://airplaneownermaintenance.com/wp-content/uploads/2017/12/IMG_7372.jpg
3. Swap EGT probs between cylinders to see if the indication follows the swap.


I was not lean of peak, it would be considered rich of peak or like 1/2" forward from stumble . Then I applied carb heat and saw the drop in egt.
 
So my mechanic determined it was running to rich. He had enriched it before, and now they leaned it out by "a turn and a half". I test flew it yesterday and is running much smoother and my climb egt reading decreased by about 20 degrees on #3. However no matter what I do in flight besides leaning to stumble, #3 is constantly in the 1540s and # 2 still showing about 1280s. That spread is still concerning. He did called Lycoming on the matter and they said that spread wasn't to be worried about as long as CHTs where under 450. I dont know my CHT, maybe I should upgrade my gauge to a unit that does.
 
So my mechanic determined it was running to rich. He had enriched it before, and now they leaned it out by "a turn and a half". I test flew it yesterday and is running much smoother and my climb egt reading decreased by about 20 degrees on #3. However no matter what I do in flight besides leaning to stumble, #3 is constantly in the 1540s and # 2 still showing about 1280s. That spread is still concerning. He did called Lycoming on the matter and they said that spread wasn't to be worried about as long as CHTs where under 450. I dont know my CHT, maybe I should upgrade my gauge to a unit that does.

What are the EGTs on 1 and 4? The issue isnt the egt sprea across cylinders, but whether or not there has been a change in readings now vs before at the same power configuration. If #3 used to run at 1300 in cruise when WOT and "1/2" from stumble" and now runs at 1540, I don't care what lyc specs are and your mechanic is "ok with it," something has happened and you should figure out what it was that happened / changed. It may me something minor that you can live with and it could also be a pre-cursor to a serious failure event. You do not want to swallow a valve one day. Not an enjoyable or inexpensive event.

My suggestion is not to accept this change as a simple matter of coincidence. EGTs do not magically rise 200 from one day to the next for no reason.

You still haven't told us where #3 used to peak. It seems you are familiar with leaning and peak EGT. We need to know this becuase any EGT higher than your previous peak EGT is not a simple mixture issue (too rich, too lean, intake leak, etc.), unless the sensor has gone bad and failing high. For example, if you used to peak at 1350 and now peak at 1540, the reason cannot be that you are leaner or richer than before, with all else being the same. Those conditions would net a new EGT below 1350. Many different reasons why you can have a higher peak EGT than yesterday, but mixture is not one of them.

Larry
 
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mixture

The mixture adjustment your mechanic made is only for idle mixture and has no effect at cruise power.
The actual number for EGT is meaningless for normally aspirated engines. The 0 320 is know for terrible mixture distribution and that will result in the wide variation in EGT. Wrap some exhaust wrap around the intake pipe on #3 and see if that drops the EGT.
You need to install CHT and if the CHT stays below 425 in climb and 400 in cruise your are ok. I think Lycoming calls for 1800 r/m or even 2000 rpm for mag check. 100 rpm drop at 1500 rpm would be ok but 100 is not good at 1800.
 
Just a thought. Are you sure you do not have a primer leak that is letting your fuel pump inject extra fuel into your engine through the primer ports on the cylinders that have them. Crack a primer line and, with the electric pump running, nothing should leak with the primer locked.
Chuck Ross RV4
 
The mixture adjustment your mechanic made is only for idle mixture and has no effect at cruise power.
The actual number for EGT is meaningless for normally aspirated engines. The 0 320 is know for terrible mixture distribution and that will result in the wide variation in EGT.

I think Lycoming calls for 1800 r/m or even 2000 rpm for mag check. 100 rpm drop at 1500 rpm would be ok but 100 is not good at 1800.

This is correct...

8213C...take a look at this DOC, it will give you some insight on operation of your carb. The adjustments that are done are only for idle, and idle mixture. Above about 1400 RPM idle fuel metering isn't delivering fuel and it's all controlled with mixture knob. This is assuming the mixture cable is installed correct and gives full control stop-to-stop on the carb.

The carb is a red-herring...highly unlikely it's causing high EGT on just #3.

This is what I would do now in the order from easy to hard, which means from cheapest to expensive.
  1. Swap EGT probes to see if the indication follows the swap, and determine if the probe is bad
  2. Compression check and borescope to check exhaust valve operation
  3. Check and test for induction leaks

One of the symptoms of an induction leak is no RPM rise when mixture is moved to idle cut-off. The fact that your mechanic enriched your idle mixture initially and you still couldn't get an RPM rise at cutoff points to this possibility. The fact that EGT is much higher on #3 than any other jug, and peaks much sooner when leaning, points to the leak being on #3. Is there a primer on #3? Check for leaks and cracks there, in addition to the intake pipe and fittings. Look for fuel staining...even mogas will leave some brownish/amber staining.
 
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Just a thought. Are you sure you do not have a primer leak that is letting your fuel pump inject extra fuel into your engine through the primer ports on the cylinders that have them. Crack a primer line and, with the electric pump running, nothing should leak with the primer locked.
Chuck Ross RV4

Cross beat me to it, but the idea is a little different. If you have a leak in the primer system that leak can suck in air when not priming, which will cause a leaner mixture on just that cylinder.
 
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