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  #1  
Old 01-20-2020, 11:25 AM
8213C 8213C is offline
 
Join Date: Jan 2020
Location: Seminole
Posts: 10
Question O-320 Help!

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?


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  #2  
Old 01-20-2020, 11:59 AM
theduff theduff is offline
 
Join Date: Jan 2012
Location: Fallbrook Calif.
Posts: 308
Default

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 ��!
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  #3  
Old 01-20-2020, 12:50 PM
DennisRhodes DennisRhodes is offline
 
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Location: Taylorsville, Ga
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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
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  #4  
Old 01-20-2020, 12:52 PM
8213C 8213C is offline
 
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Location: Seminole
Posts: 10
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Quote:
Originally Posted by theduff View Post
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.
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  #5  
Old 01-20-2020, 01:20 PM
avrojockey's Avatar
avrojockey avrojockey is offline
 
Join Date: Aug 2019
Location: Appleton, WI
Posts: 320
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Quote:
Originally Posted by 8213C View Post
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?


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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Last edited by avrojockey : 01-20-2020 at 01:30 PM.
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  #6  
Old 01-20-2020, 01:26 PM
8213C 8213C is offline
 
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Location: Seminole
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Quote:
Originally Posted by DennisRhodes View Post
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.
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  #7  
Old 01-20-2020, 01:33 PM
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avrojockey avrojockey is offline
 
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Quote:
Originally Posted by DennisRhodes View Post
Another thought would be to swap the #3 EGT with another cylinder to see how it reacts.
Do this too ^^^^^
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  #8  
Old 01-20-2020, 01:48 PM
patterson patterson is online now
 
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Location: Queen Creek AZ
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Default 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
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  #9  
Old 01-20-2020, 01:53 PM
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avrojockey avrojockey is offline
 
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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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Last edited by avrojockey : 01-20-2020 at 02:00 PM.
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  #10  
Old 01-20-2020, 02:00 PM
RVDan RVDan is offline
 
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Location: Frederick, MD
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Quote:
Originally Posted by 8213C View Post
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.
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