Rough O-200

[Eric Brown]

Started my freshly field overhauled O-200 for the first time, today. Engine is in a C150. The engine has a scatter miss below 1200 RPM. Is the same on either mag. Mixture setting makes no change. Both mags were oh'd. Carb was oh'd with latest float and nozzle. Above 1200 RPM it is smooth with 50 RPM mag drops. Almost feels though one cylinder is not firing all the time. Sticky valve ? Have not run above 1500 RPM.
Has new Millenium cylinder assemblies. Whada ya think ?

[Tom Downey]

Started my freshly field overhauled O-200 for the first time, today. Engine is in a C150. The engine has a scatter miss below 1200 RPM. Is the same on either mag. Mixture setting makes no change. Both mags were oh'd. Carb was oh'd with latest float and nozzle. Above 1200 RPM it is smooth with 50 RPM mag drops. Almost feels though one cylinder is not firing all the time. Sticky valve ? Have not run above 1500 RPM.
Has new Millenium cylinder assemblies. Whada ya think ?

Do you have the Intake spider mounted to the case with the proper stat-o-seals? Check the IPB to see the part number.

these symptoms are typical of a carb/intake spider that is mounted solid.

[jam0552@msn.com]

Measure spark plug resistance with Volt-Ohm Meter. If greater than 6000 Ohms, you need new spark plugs. With such high resistance the spark is very weak, which manifests in rough running at low RPM when fuel/air mixture is very lean. Increasing RPMs increases fuel air mixture and engine smooths out.
Joel Marketello

[Eric Brown]

I do have new stat-o-seals at the spider mount. All spark plugs are new, but I could check each one just in case. I'll let you know.

[Tom Downey]

Next step, sniffer test around all of the intake hoses. see if the engine surges when a little WD 40 is applied at each hose. (both ends)

After that, disconnect the primer line and cap it at the spider.

[Bill Greenwood]

Unlikely that new plugs are the fault. There are advocates of 6000 ohms resistance being significanat and others who say if it fires well on the screen under pressure testing it should be good. A defectivee plug is not likley to clear up at 1200 rpm unless it was fouled, and then more likely to need more rpm to burn off.
The carb may have problems at idle and low speed and then engine runs good when it is on main metering system above 1200.
If you start engine from cold and it fires right up it is likely that ignition system is good. You can start from cold,run 20 sec with it missing, then shut down and check which if any cylinder is cold or if any spark plug is cold, ie not firing.

[L16 Pilot]

I'd tend to agree with Bill on this one. I've seen "overhauled" carbs that show the described conditions coming off the idle circuit on to the main circuit usually due to the passages not cleaned out completely or have sat around with old fuel in the bowl.

[Bill Greenwood]

Eric, what brand of spark plugs do you have? The issue of resistance is emphsized by Tempest. Seems to have come to the fore in regards of Cirrus and lean of peak running where is it claimed a problem with Champion. I havent heard much about this in the last year, and Champion has a new design of part of their plug, I have used Champions for decades, never had much trouble other than a cracked one. I do know of cases where the pilot thought engine was running fine, no complaints and then tested resistance and decided the plugs were defective on that basis. I rely on mag test while runnng or on pressure tester when plugs are serviced. I have checked resistance but only changed one plug on that basis. A C150 engine should be easy on plugs, not demand much.
Let us know what you find asap?

[Eric Brown]

Gentlemen.
Here's what I have done so far. Visual check of induction system. Different spark plugs. Tried another O-200 carburetor. Removed both ignition leads from one cylinder at a time and ran engine below 1000 RPM to see if miss would disappear with the dead cylinder. Tried setting the idle mix very lean (1/4 turn). Tried very rich mix (3 turns). The miss is still present below 1200 RPM.

Riddle me this. If the crank and cam gears were off by 1 tooth, would this create this problem ???? There were no index marks on my gears. I set them by feel of the #1 cylinder valve overlap per the OH manual.

[Bill Greenwood]

I dont know about setting gears. But youve ruled out plugs and carb it seems. So, sounds silly but Check each ignition wire with a lead tester as well as visual and that they are connected correctly, I have seen this switched.
My next gu ess is a valve problem, and a compression test may find any valve leak, wont be surprised if you dont find one. A sticking valve is most likley on a engine started cold. That sort of leaves mags, but cant see how they would clear up at 1200 rpm, but may be worth a look inside for a crack or crack in cap and the timiing setting.
It would be worth a phone call to try tech support (770-358-4430)and just might be able to help.

[Tom Downey]

Gentlemen.
Here's what I have done so far. Visual check of induction system. Different spark plugs. Tried another O-200 carburetor. Removed both ignition leads from one cylinder at a time and ran engine below 1000 RPM to see if miss would disappear with the dead cylinder. Tried setting the idle mix very lean (1/4 turn). Tried very rich mix (3 turns). The miss is still present below 1200 RPM.

Riddle me this. If the crank and cam gears were off by 1 tooth, would this create this problem ???? There were no index marks on my gears. I set them by feel of the #1 cylinder valve overlap per the OH manual.

First of all, set the idle mixture by allowing the engine to run 3 minutes, then pull the mixture to idle cut off (full lean) and watch the tach, you should get a 10-to-50 RPM rise as the engine dies, above 50 lean it, below 10 enrichen it. after that leave it alone.

Next, when you have no timing marks. you must inspect for them prior to teardown, If you don't have any place #1 cylinder at TDC by the crank flange and mark the gears.

So that has not been done, we are now guessing where the gear goes.
To dial in the cam gear, you need two dial indicators, set them up on the two rocker arms to both valves in #1 cylinder turn the crank and watch the opening and closing of each valve, When #1 cylinder is at TDC on the compression stroke, the two valves should be midway between touching there respective cams. Both should be fully closed.
To change the gear mesh, remove the crank gear, and rotate the cam, then replace the crank gear.

Now that we've been thru that, answer this, is this engine making full power, as in does it make rated RPM static. If it does the gears are correct.

If you wish to send me the cam gear I will place the correct timing mark on it.

PM me for the address if interested.

[Eric Brown]

I've run the engine with the idle mixture very lean (1/2 turn) and very rich (3 turns).No change. I did the gear meshing procedure during assembly. No dial indicators. I used my fingers to feel. It always came out within 1/2 tooth.

NEW SUFF. Removed entire induction system and inspected. Installed new intake elbow gaskets. No change. Ran on a cool morning. The missing was worse, especially on RH mag (top plugs). Cyls 2 & 4 were the hottest. 1 & 3 were the coolest (not by much). Engine still runs fine above 1300 RPM. Have not run engine above 1700 RPM. Still feels like one cyl. just cuts out.
Am going to try an old ign. harness on RH mag.

[Eric Brown]

GENTLEMEN;
This one is "kicking my butt". No progress. I removed the RH Bendix mag and installed a Slick 4001 with it own harness. No change. It's not mags, harness, plugs, carb. primer, induction leakage, or idle mixture. The only thing left is sticking valves and these are new Millinium cyl. assemblies. Any additional ideas ?????

[Sam Buchanan]

I know this sounds too basic.....but are you positive you aren't experiencing carb ice? The O-200 on my Fokker replica will ice like crazy while taxiing for the first take-off of the day (the carb is still cold). It will run rough up to about 1200rpm until carb heat is applied.

[skyfixer8]

I would go with possible carburetor problem and ask, was it overhauled by aviation carb overhaul shop or someone local ? I have seen some bad ones done by people who don t do it completely. Also, if it has new one piece venturii, was the "flash" left by manufacturing process cleaned off before installation ? Just listing some of the things I have seen over the years. Also, was new gasket installed between carb and intake mount ?

Bill L

[Bill Greenwood]

Bill L. you may have missed it but Eric wrote that he had tried an entirely different carb on the engine and no improvement, same as he tried other plugs, other mag , other harness. etc.

[Bill Greenwood]

Eric, when you tried the new mag was it with an whole new cap and harness? Caps can have fine cracks.

And since we are at the Ouiji board stage, are you sure the engine is missing and not just a vibration. I once in flight lost an entire cylinder on at 4 cylinder 0360 in a Mooney and it was definterly rough no doubt about . Turns outh the OH had not secured the valve guide right and it worked its way out of the head and hammered both plug gaps closed.

I once had what I thought was a miss on cliimb out in my TSIO 520 in Bonanza, just a slight rough, could see it in the magnetice compass rocking. All gauges normal , but with a passenger and rougher terrain ahead I returned to the ariport and took an airline. Didnt get attacked by thugs on the ariline and had the equivalent of a checkup and tuneup on the plane the next 2 days. No problem found. Came back to fly home and still the same, a very slight vibration, worse with more rpm. Decieded it was not a miss but a vibration and took it to the shop. And a simple answer was found, where the deice boots on the prop went into the hub, a small piece of rubber had come off, hard to see, and just enough to slightly unbalance prop. So small that putting one tie wrap on the base of the prop made it smooth again.

The hard part on yours is clearing at 1200? Try that phone number I gave, supposed to be an expert on this engine.

[Eric Brown]

Gentlemen, I think this will be my FINAL REPORT.
Took cold compression checks. All 77/80. Confirmed correct crank to cam gear indexing thru the RH mag mount hole. Reinstalled RH Bendix mag. Swapped spark pugs top to bottom. No change. Don't believe it is a vibration. It's scatter miss. Da......... da ......da..da..da...................da .......da.da.......... Shakes the airplane. Put the cowling on it and took to full power. Turns a smooth 2425 RPM with a Sensenich 6948 prop. I'm going to use it this way and see if it may improve (spook theory) over time. Figure to have the airplane back together and flying within 30 days.

[Bill Greenwood]

Eric, is "spook theory" like elves theory? That is overnight a group of magic elves , all a&ps, sneak into the hangar and clear up that little miss.

There are engines that just run smoother above idle. My Tsio 520 is slightly rough below 1000 and much smoother at just 1100. Lots of Merlins will pop, bang and even backfire near idle, and smooth as anything above 1500. Some of this is due to an aggressive cam profile probably due to overlap, dont know why it would be true in a simple 0-200? I once had a small homebuilt that sounded like a trash can of loose rocks at idle but flew well, but that was a 2 stroke Rotax 337.
Its unlikely you are going to have a grahic engine monitor in a C-150, but if so it would confirm the miss as well as show if it is consistently on just one cylinder each time. Aanyway stay near the runway on your first flights, and please keep us posted on this, even if only that it flys well when not at idle.

[rwanttaja]

I know zip about engines. Our Fly Baby engine guru has chimed in on similar problems in the past, and I keep his responses online:

http://www.bowersflybaby.com/tech/fenton.htm#a65_hesitation

It's a tale of woe with similarities to yours. In the later sections of this, he mentions that spark plug problems can manifest problems only under pressure or after a few minutes operation. Though it sounds like you've pretty much eliminated the electrical bits from the problem.

Here's someone with an O-300 (which, believe, uses the same cylinders as the O-200) with a miss, where where the guy describes the missing almost identically to you. In this case, our guru suggests potential valve/lifter issues.

http://www.bowersflybaby.com/tech/fenton.htm#O-300_Missing

Just throwing these out there for you.

Ron Wanttaja

[Tom Downey]

Gentlemen, I think this will be my FINAL REPORT.
Took cold compression checks. All 77/80. Confirmed correct crank to cam gear indexing thru the RH mag mount hole. Reinstalled RH Bendix mag. Swapped spark pugs top to bottom. No change. Don't believe it is a vibration. It's scatter miss. Da......... da ......da..da..da...................da .......da.da.......... Shakes the airplane. Put the cowling on it and took to full power. Turns a smooth 2425 RPM with a Sensenich 6948 prop. I'm going to use it this way and see if it may improve (spook theory) over time. Figure to have the airplane back together and flying within 30 days.

Your two symptoms of, it runs worse in cold weather, and it makes no difference where the idle mixture is set. makes me believe the carb idle circuit is not providing enough fuel when you are below the RPM of the cruise circuit.

So my question would be, Is this a newly rebuilt Kelly carb?

[Bill Greenwood]

Tom , remember Eric said he had even tried a totally different carb and no improvement. And if carb is really lean at idle then it would likely be hard to start, need a lot of prime and die soon when on idle. And there isnt a fuel pump in the system so even less to go wrong.

Eric , a very long shot, but I tallked to an a&p working on a C172, and he said to look in exhaust pipe that sometimes baffles can come loose and partially block it.About the only other thing you havent mentioned it the door for carb heat. Is it secure and off when you are running the engine? Even carb heat partially on would enrich the mixture, but hard to see how it would be the miss you describe.

[Tom Downey]

Tom , remember Eric said he had even tried a totally different carb and no improvement. And if carb is really lean at idle then it would likely be hard to start, need a lot of prime and die soon when on idle. And there isnt a fuel pump in the system so even less to go wrong.

Eric , a very long shot, but I tallked to an a&p working on a C172, and he said to look in exhaust pipe that sometimes baffles can come loose and partially block it.About the only other thing you havent mentioned it the door for carb heat. Is it secure and off when you are running the engine? Even carb heat partially on would enrich the mixture, but hard to see how it would be the miss you describe.
This would not be the first time I've seen two messed up carbs. and most folks start on primer fuel. and run above the idle circuit RPM.

It would seem anyone assembling a new engine would inspect the mufflers they install.

[Bill Greenwood]

Tom, re carbs, read Eric's first post again. The carb was Overhauled, along with mags etc. Then he even tried a complete 2nd carb with No change, No improvement, He doesnt say but Id guess the 2nd card came from an engine where it ran properly.
So we can believe in the improbable that both carbs were, as you say, "messed up" with the same defect or more likely that as much as this sounds like a carb problem it is really something else.
He could take his components, carb, mag etc, and run them One at a time on another engine that has been running well and see if he can duplicate the problem, thus isolating the cause, but that is a lot of trouble.

[Tom Downey]

Tom, re carbs, read Eric's first post again. The carb was Overhauled, along with mags etc. Then he even tried a complete 2nd carb with No change, No improvement, He doesnt say but Id guess the 2nd card came from an engine where it ran properly.
So we can believe in the improbable that both carbs were, as you say, "messed up" with the same defect or more likely that as much as this sounds like a carb problem it is really something else.
He could take his components, carb, mag etc, and run them One at a time on another engine that has been running well and see if he can duplicate the problem, thus isolating the cause, but that is a lot of trouble.
When he says the carb was overhauled, that is why I suspect the carb, Overhauled by who? the rest of your guess is just that, it would be pretext by he had several other engines to test stuff on. most don't.

[Bill Greenwood]

Tom, seems we have a communication problem, or just are thinking opposite.

Erics first post points out that the carb is overhauled, just as engine and mag are OH. So the carb seems suspect for the low speed miss. However in post #9 Eric writes "tried another O 200 carb", no improvment . Did you see that post?. So if the O H carb was the problem it is not likely that it would continue the same way with the 2nd carb. And he tried a 2nd mag and 2nd set of plugs so the problem is likely to be elsewhere.

I dont really understand the wording of your last sentence. My point is that another way to test a suspect carb or mag etc is to put it one at a time on a good running engine and see if the miss then transfers to theg good engine. If not then the item is not where the fault lies.

And Eric any updates for us? I really would like to know what cures this in the end

[Tom Downey]

Tom, seems we have a communication problem, or just are thinking opposite. that's the problem with trouble shooting on line, you never know all it requires to get it right. all you can achieve is a SWAG.
You don't know who overhauled what, or what the OP used to determine what the problem was. So all you can do is guess, So don't get indignant when I disagree.

[Bill Greenwood]

Tom, The trouble must lie with the first carb, the overhauled one,just as you say, even when it is no longer on the airplane, . Why couldn't I see that all along,rather then trying to discuss the symptoms and what Eric had already checked and ruled out?

So it must be the carb that was overhauled, and even when it is not on the engine, it must have left negative vibes, that only occur under 1200 rpm.

We once actually had trouble with an ovehauled carb on a SNJ, got it back from the oh shop and while the plane would start and run it would die at idle, Turns out the oh shop does a lot of duster engines which spend a lot of time idling and the shop had set the float level like they do in dusters, thus too lean for the SNJ.

[Eric Brown]

Gentlemen;
I have been to the Flybaby website and reviewed every condition I thought held some merit. I have recently installed the wings onto the airplane.
I have run the engine once since then. The miss and vibration were NOT as predominate as it was with the fuselage alone. Larger mass absorption ?? I have run several airplanes without wings that had small Continentals and did not experience this type of miss. At this point, all I can figure is that, mechanically (other than a possible lifter problem), there is nothing seriously wrong with this engine. Hopefully will fly I the next 30 days and re-evaluate.

PS: about the carbs. The original carb a 10-4115-2, I overhauled (A&P / IA). The second carb a 10-4894, overhauled in 1997 by Consolidated Fuel Systems and has 500 hrs SOH.

[Tom Downey]

Bill, I have been rebuilding and repairing 0-200 and 0-300 Continentals for nearly 60 years. In that time period I have learned that the 0-200 was built by Continental.

Next, how can any A&P rebuild a MA3-SPA carb and call it overhauled?
read FAR 43.2 and tell me how any A&P in the field can test it as required by the overhaul manual.

[Tom Downey]

Tom, I and others on this topic should accept your diagnosis. The trouble must lie with the first carb, the overhauled one,just as you say, even when it is no longer on the airplane, . Why couldn't I see that all along,rather then trying to have a logical discussion about the symptoms and what had already been checked?
And Im glad we disagree, if you agreed with me, I'd assume that I was wrong and change my opinion. And I dont have much experience with engines, other than Air Force mechanic school and owning and flying three small 4 cylinder Lycomings for 10 years or so, unless you count the decades of partial working on engines from small single cylinder to V-12s, in motorcycles, cars and airplanes.
So it must be the carb that was overhauled, and even when it is not on the engine, it must have left negative vibes, that only occur under 1200 rpm.
I am having some trouble with my car, a miss or cutting out a low speed. I took it to the shop and told them it must be the overhauled carb, and they looked at me kind of funny and claimed it had fuel injection instead of a carb. Im going to try another shop that might be able to find the defective carb hidden in that engine.
We once actually had trouble with an ovehauled carb on a SNJ, got it back from the oh shop and while the plane would start and run it would die at idle, Turns out the oh shop does a lot of duster engines which spend a lot of time idling and the shop had set the float level like they do in dusters, thus too lean for the SNJ.
And what does all that have to do with the ability to trouble shoot on line? All my years dealing with customers has taught me the only way to trouble shoot any problem is to do the whole job yourself. Step by step, square 1 step 1 to finish, Believe it or not you can't do that thru the computer screen. So don't get all up tight because somebody calls you on it.

[Tom Downey]

Gentlemen;
I have been to the Flybaby website and reviewed every condition I thought held some merit. I have recently installed the wings onto the airplane.
I have run the engine once since then. The miss and vibration were NOT as predominate as it was with the fuselage alone. Larger mass absorption ?? I have run several airplanes without wings that had small Continentals and did not experience this type of miss. At this point, all I can figure is that, mechanically (other than a possible lifter problem), there is nothing seriously wrong with this engine. Hopefully will fly I the next 30 days and re-evaluate.

PS: about the carbs. The original carb a 10-4115-2, I overhauled (A&P / IA). The second carb a 10-4894, overhauled in 1997 by Consolidated Fuel Systems and has 500 hrs SOH.
You do realize that the 0-200 with its remote mounted carb, is a known ice maker. they do make ice at idle on the ground.

At next run, feed it some hot air, use a hair dryer if need be.


have you run a cold cylinder test?

[Bill Greenwood]

I dont have much experience working on 0-200. mine is a C90, the predecessor to the 200. . And are vast differneces between C-90 and 0-200 and the small Lycoming 4 cylinder engines?

As for the difficulties of diagnosing on line, we dont have to do that, youve already done it and it was the carb overhauled by someone else, that must be the problem.
As for dealing with customers, Eric as an A&P/IA himself is more qualified than just a pilot owner.

For now, we can Politely disagree on the cause, hopefully without rancor or personal insults and maybe Eric will soon find definitley what the defect is.
And it is possible that both carbs, even though overhauled or to use your term rebuilt and by different people are defective, they could have some gum from fuel in the idle circuit.

I realize that although I like a good discussion of the facts and theories, that some people are not made that way and get uncomfortable with it. I do want to know the final answer to this riddle even if we may not get it.

[Eric Brown]

Next, how can any A&P rebuild a MA3-SPA carb and call it overhauled?
read FAR 43.2 and tell me how any A&P in the field can test it as required by the overhaul manual.[/QUOTE]



If you state that you overhauled in accordance with the current overhaul manual, you are in compliance with FAR 43.2. There is nothing so specialized in the MSACSM, rev 1 overhaul manual that can't be performed by a GA shop. Not all specialized tools will be needed. Equivalents can be found for those tools that are needed. The M-5 float gauge will be needed. The float valve and seat test can be performed with fuel in a standpipe and 6 psi of air pressure.
What part of the overhaul requirements would an A&P not be able to accomplish ?

[skyfixer8]

I would like to throw my 2 cents worth into this post about the carburetors. Although both part numbers that were given . 10-4115-2 and 10-4894 are correct for the TCM O-200. the 10-4115-2 was superseded long ago by the 10-4894 which , if overhauled by a shop should have been upgraded to a 10-4894-1 or -2.

Bill L

[Tom Downey]

Next, how can any A&P rebuild a MA3-SPA carb and call it overhauled?
read FAR 43.2 and tell me how any A&P in the field can test it as required by the overhaul manual.
If you state that you overhauled in accordance with the current overhaul manual, you are in compliance with FAR 43.2. There is nothing so specialized in the MSACSM, rev 1 overhaul manual that can't be performed by a GA shop. Not all specialized tools will be needed. Equivalents can be found for those tools that are needed. The M-5 float gauge will be needed. The float valve and seat test can be performed with fuel in a standpipe and 6 psi of air pressure.
What part of the overhaul requirements would an A&P not be able to accomplish ?[/QUOTE]

Kelly now owns the production certificate, they do not supply the overhaul manual for their carbs. any manual you see is a old Marvel or Precision manual, and no longer used. Kelly is now the only one that can legally overhaul the carbs by the manual. then test as required on a flow bench. the rest of us can only repair.

[Eric Brown]

Even though Kelly does not supply an overhaul manual, earlier manufactured carbs can still be overhauled under the older Marvel and Precision Aircraft overhaul manuals. In a decision out of the 1990's, the FAA considers the earlier manuals to be "current data" as long as the carb was manufactured during or before the time that the earlier manual was current. This would make an overhaul of an earlier manufactured carb to be in compliance with FAR 43.2 and 43.13(a). The only additional requirements for the overhaul would be the compliance of ADs issued against the carb up to the date of overhaul.

Now, ...... a civil court may have a different opinion !

[Tom Downey]

Even though Kelly does not supply an overhaul manual, earlier manufactured carbs can still be overhauled under the older Marvel and Precision Aircraft overhaul manuals. In a decision out of the 1990's, the FAA considers the earlier manuals to be "current data" as long as the carb was manufactured during or before the time that the earlier manual was current. This would make an overhaul of an earlier manufactured carb to be in compliance with FAR 43.2 and 43.13(a). The only additional requirements for the overhaul would be the compliance of ADs issued against the carb up to the date of overhaul.

Now, ...... a civil court may have a different opinion !

Nice,, now where are ya going to get new parts for them?

[Bill Greenwood]

Eric, since Tom has been doing 0-200 work "for 60 years", perhaps he has a current overhauled carb for them, maybe even a Kelly one, that he would loan you to try on your engine, with the agreement that if it cures your miss, then your carb was indeed the problem and you pay Tom a generous price for his carb plus shipping. If not you return it as received, paying shipping both ways.
I want you to fly safely when and if you do get in the air, but Id also really like to know the answer to the riddle.

[Tom Downey]

Just buy a new one.

[Eric Brown]

Gentlemen;

I have now flown the engine for 2hrs. It performs well. 2550 RPM on climb and 2750 in level flight with a 6948 prop. The roughness below 1000 RPM is now minimal. Idle is 650 an idle mix is +25. SPOOKS ? I thank everyone for their advise.