Paradise Lost

Paradise Lost

<HTML>Geez, I fired up my C150H at the crack of dawn Sunday and it ran just as it did before $2000 worth of repairs. Still hesitates below 2000 rpm when the density altitude is low. The pipes are dry and she burns 5.0 gph with no leaning and 100% throttle 50% of the time and 75% the other 50% of the time. New carb, overhauled induction system - what's left. I beginning to think the wag who suggested the carb jet is too small is right.  Perhaps the millinium cylinders and pistons are mismatched? Seems to me every possible root cause must be eliminated before attempting a larger jet. Is it even possible to re-jet legally?</HTML>

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Re: Paradise Lost

<HTML>The mechanic just did a full evaluation at 07:00 this a.m. and the motor performed perfectly. He suspects carb ice. However, the relative humidity was 10% Sunday morning with a huge dew point spread (Santa Ana winds). Another theory is a piece of the tube coil is still floating around and shorting out a plug. Sticking valves are also a possiblity. He says jets are never changed on the O-200-A. Help - am I looking at replacing a "haunted" motor?</HTML>

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Re: Paradise Lost

<HTML>Out of curiosity; have you had the mags checked??  Looks like the only thing you haven't gone through is the ignition system (unless I missed an earlier post).

Does it act the same when you cycle the mags from R/L/Both ??</HTML>

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Re: Paradise Lost

<HTML>Both Slick mags were new in 1997 with 80 hours on them now. Both just had complete 500 hour inspections at the annual (60 hours on the mags) because at the time we did not know how new they were. At runup they are dead on the same with 25 rpm drops and no variance. The timing is 28 degrees. Cycling the mags appears to have no impact on the problem. I suggested to my mechanic today that they might have BOTH been reassembled incorrectly in the same way during the 500 hour inspection. He says they usually work right or not at all. The problem essentially is at times you must advance the throttle very slowly or the engine balks or even dies in the 500-2000 rpm range.</HTML>

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Re: Paradise Lost

<HTML>After reading some of the other c-150 threads, could you have an obstructed or partialy obstructed fuel cap vent or crossover ventline? Faulty venting could cause a partial fuel flow and lean mixture that would be impossible to fix with carb adjustments. Could be right on the edge of fuel starvation? Maximum RPM sets up a vibration that temporarily dislodges the obstruction. Or maybe an RPM range sets up a vibration to cause the obstruction. I know it's way out in left field , but I'm used to having problems nobody else has ever had and things break for me that are indestructible for other people.    Joe</HTML>

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Re: Paradise Lost

<HTML>The balking during rapid advancement of the throttle....I had a similar experience...it was due to the accelerator pump not pumping.  If that extra squirt of gas doesnt happen, the engine will sputter and maybe even die because the wide open throttle sucks a sudden bunch of air without added fuel.  It takes a moment for the vacuum in the manifold to build and "suck the gas out of the jets" <very non technical explaination>
With all the work you had done, not counting the new carb, one would ASSUME that the carb isnt the proplem...I think if you push the throttle in and out a couple of times, when not running, you might be able to detect gas dribbling down.
Just a thought...
Michael</HTML>

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Re: Paradise Lost

<HTML>Pump it a few times and if the pump is working you WILL have fuel dripping!!!  (Yes, while working to lube the throttle cable I was pumping it when our A&P friend yelled from the front that I was washing the hangar floor with av fuel :-) )</HTML>

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Re: Paradise Lost

<HTML>Others have already mentioned the accelerator pump.  The pump lever has 3 holes in it for adjustment.  Normally the middle, or #2 hole is used.  But number 1 hole gives a shorter stroke (less fuel) and us sometimes better for hot weather or "high test" fuels (quotes are mine, to emphasize the mfr's wording) and No. 3 hole may be required in extremely cold weather (or dense air) weather.</HTML>

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Re: Paradise Lost

<HTML>The problem is identical with both the old and new carbs. When I pump the throttle a large puddle of fuel is created on the tarmac. It so happened that we used the same accelerator arm hole on the new carb as on the old one. Don't know which one, but we'll get right on it.

My latest epiphany is - THE PRIMER PUMP!  let's consider the evidence:

1) it works poorly. When I pull it out the first time it feels spongy as if the system is full of air and pushing it back in supplies very little fuel.

2) When pushed in it often hisses.

3) After priming I give the handle a good tug out to ensure that it is latched.

4) I have a faint recollection of manhandling it somewhat is the recent past.

5) Could be sealing intermittently based on how it was used and chance.

6) The theory has much merit except the pump does not seem to ever leak fuel.

At any rate, I think I'll replace the pump before entertaining my mechanics "$1000 a cylinder" top-end inspection fee. At this rate I might as well cut bait and get a brand-new motor.</HTML>

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Re: Paradise Lost

<HTML>Oh yeah, we did a fuel rate test - like a cow peeing on a rock. malfunctioned before and after the test.</HTML>

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Re: Paradise Lost

<HTML>  As I mentioned before, the only time I ever lost an engine in that RPM range was when the primer was loose on a Piper.

1000-1700 became unusable RPMs for me. 

  I suppose it would be easy to check.  Couldn't a mechanic just unhook the primer lines and plug them?  Then check the engine? 

  More brainstorming, I think I remember the primer is only hooked to three (not four) cylinders.  So if you have a four probe EGT/CHT, if you run the engine for a while in "sick" mode (sputtering and such), the three cylinders sucking extra fuel out of the primer and flooding will show different temps compared to the unprimed cylinder?

  Hmmm...I replaced the little o-ring on my primer once.  The old ring had suddenly given out (just went in and out fast, no fuel pumped).  Ask a mechanic if this is stupid, but maybe you can try running the engine with the primer removed and see what happens.  Maybe it's sucking extra fuel, or maybe it's sucking air in.

  Dunno, if the engine was getting extra air in the cylinders through the primer lines, would that cause this kind of problem?

  Hmmmm...

Mark</HTML>

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Re: Paradise Lost

<HTML>Thanks Mark and I'm sorry for overlooking your previous primer comment. My suspicion is the motors sucking extra air. The four EGT readings are very similar except for the newly overhauled #1 jug which runs slightly higher. My POH has a drawing depicting primer lines going to all 4 cylinders. Seems like it would be simple to plug the lines as you describe. I hope my mechanic has the pump out and is seeing what kind of suction can be substained on the outlet line while manipulating the plunger.</HTML>

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Re: Paradise Lost

<HTML>Say Mark, what kind of motor was in the Piper?</HTML>

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Re: Paradise Lost

<HTML>William, I know this probably won't help, but almost all small Continental engines(0-200 & smaller) that I have flown behind have exhibited this type of behavior when it is cool or very low humidity conditions. I had an A-65 in a T-craft that always did this, and flew a J-3  and a C-150 that acted the same way. Let the weather warm up a little, and the hesitation goes away. My way of dealing with this was to just ease into the throttle a little extra smooth when it's cool. I hope this helps. Good Luck.</HTML>

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Re: Paradise Lost

<HTML>Geez Greg, what a breath of fresh air. Maybe there's NOTHING wrong with the motor and I just need to learn to operate within it's idiosyncrasies.</HTML>

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Re: Paradise Lost

<HTML>My mechanic finally reproduced the balking throttle problem and promptly grounded the airplane. It happens when it's cold out (SoCal cold - 50 F). He bypassed the primer pump with no impact on the problem. He found the carb ice probe was leaking and plugged that to but still no impact on the problem. Next step is to use a more agressive hole on the accelerator pump arm. He exhaustively studied the intake valve chambers for leaks and found none. Stay tuned - it's getting weird.</HTML>

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Re: Paradise Lost

<HTML>I'm insisting that the mechanic check the entire primer system. I suggested plugging the primer port on each cylinder for a test. Seems a leak anywhere in the system would impact all the cylinders as the lines are common. Some say an induction leak would produce a rought idle (which I don't have), but someone pointed out here already that the idle system would enable a smooth idle. i can't think of anything else that could cause the leak. Perhaps all the cylinders were manufactured incorrectly and are leaking at say the cylinder head joint. Why not check the compression with the cylinders at the bottom of the compression stroke?</HTML>

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Re: Paradise Lost

<HTML>Forget the primer theory - only one to the carb and has already been plugged.

Just got off the phone with the mechanic - the timing was 24 and 26. Gads we just set it to 28 and 28 after finding it at 22 and 24 fresh from the annual. Looks like the timing is drifting around!</HTML>

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Re: Paradise Lost

<HTML>Now there is talk of problems with the mag drives on the back of the engine. Sounds expensive!</HTML>

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Re: Paradise Lost

<HTML>My current theory is the mag impulse couplings are hanging up because of incorrect assembly or lubrication. The mags seem to be affected by their temperature. Both mags were completely disassembled and reassembled just a few hours before the problem began.</HTML>

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Re: Paradise Lost

<HTML>I recently had my Mags overhauled again.  But it was done by the engine overhauler.  My understanding is that the Mag should only be disassembled and reassembled by an authorized overhauler or Manuafacturer; Not a mechanic.  The way you stated it, it sounds like the Mechanic did it.</HTML>

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Re: Paradise Lost

<HTML>I have had a simular problem with an O-200.
The problem turned out to be the carbuerator mounting gasket. The hole in carb gaskets always seem to be too large and in some cases can create turbulance between  the mating surface of the carb and mounting flange.
I have been caught with this once and have since always made my own custom fitting gaskets and have had no more problems.
HD</HTML>

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Re: Paradise Lost

<HTML>I will ask the mechanic about possible disruption of the mixture flow due to a poorly fitted gasket. However, the gasket looked great to 3 different mechainics.

The shop that did my annual insisted on a 500 hour inspection for my mags because the log showed mags with other serial numbers were installed in 1980. Later, after the annual, I found tags indicating the current mags were installed in 1998 and have less than 100 hours. They billed me 3 hours for the inspection which they said involved a complete disassembly. They have told me recently that they have a complete mag facility including a test machine which could test my mags "all day" if required. When I told them that the timing is wandering they wanted me to get the mags back to them right away. I think I'll let the current mechanic do the forensics on the mags. I spent the weekend studying an A&P textbook from Northrop that used a Slick mag similar to mine as an example. It appears that there are numerous opportunities to assemble them incorrectly. For example there are two different alignment marks for meshing the gears based on the direction of rotation. Also, the nylon gears are supposed to have considerable backlash when cold to compensate for significant expansion when warm. I wonder about the impulse couplers. Maybe there is too much tension in the system causing them to bind. There is oil leaking from one of the mag to assessory case junctions. The engine runs fine when it's hot out and when it's cold out at steady rpm. The motor runs smooth on either mag, the drop is 25 rpm for each.

My question is - could the timing be retarted on one or both mags for what ever reason on a cold day, and if so, could that cause balking in the 1500-2000 rpm range?</HTML>

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Re: Paradise Lost

<HTML>Geez, the mechanics says the mags are like new inside.

He says's he's starting from scratch now evaluating the cam, lifters, and push rods.

How much does it cost to replace an O-200-A?</HTML>

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