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0320 150 loosing power?

scottsville

Registered User
HI, I have a super cub 150 and over the last year or so it seems its been loosing power. It used to climb out and around 2500 to 2550 rpm with a borer 80-44. Now I am getting about 2400. about 6-700 ft per min. which I used to see around 1000. It seems to be a coming on gradual. I am thinking it is either the carburetor or muffler. Its only got 400 hours on a penn Yann overhaul.

Just checking to see if anyone has had this same problem or knows where to start 1st?

Thanks in advance!

Scott
 
Check the exhaust to be certain baffles haven’t broken and partially blocked exhaust pipe. Does your muffler have the bail?

MTV
 
That, and check the ignition timing.

One of the guys likes to climb out flat, and never noticed. I made a take off to bring it home, and it would not climb. Found both mags worn so far they could not be re-timed. Swing-out engine mount made my job easy.
 
Do you have SLICK mags? Do a mag check at 2400 RPM. Make sure the carb bowl is not loose ( air filter moves or blue streaks on carb bowl, big RPM drop with carb heat.) Check everything the others have said.
DENNY
 
Where do you live? My first response would be to put some isopropyl fuel additive in. A little drop of water in the carb bowl does what you describe.
 
Could you clarify please? I was under the impression that the only drop limit is a max limit. Also, altered point setting will affect mag-to-engine timing, so seems that would be the quick check? I'm interested in your thoughts, thanks.
 
The peak magnetic flux flow through the primary winding of the coils is when the magnet rotation is just coming up on the leading edge of the E-gap. E-Gap is the flat spot where the direction of magnetic field reverses. To get the most power in the secondary winding the points must open at the instant of maximum flux. Over time with the wearing of the points or the cam follower the relationship of the point opening to the maximum flux changes. As this change takes place the spark timing and strength changes/weakens. This changes the timing to the top dead center of the piston and increases the amount of mag drop when you switch one mag off.

The limit you mention is just that, a recommended limit. 75 rpm drop is higher than it could be when everything is set to optimum. The change from optimum to maximum takes place over time. A perfectly timed mag will have very little drop.
 
Ok. I will find borescope and check it out. What do you mean by bail? Sorry not a very good mechanic.

Take a flashlight and look up the tailpipe. See anything loose? anything that might block the tailpipe outlet? If a bail has been welded on, it will look like two wire arches positioned to keep stuff from covering the tailpipe outlet. If you find ANYTHING that's loose in the muffler, pull it and have it repaired immediately, before further flight.

Web
 
Pete, I understand the e-gap idea, however 75 is about the drop I've always had at 1800 nominal RPM, including with several iterations of newly overhauled Bendix mags. So seems to me it's about right. That's with external timing right on 25 deg. Thinking a flatter prop might yield less drop? Mine is 82-42.

Edit: let me re phrase that, ive never seen less than about 75. So dunno what I'm missing?
 
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Gordon, The Bendix manual tells you to set the point opening at a specific angle of the cam. I don't do that. If you set it as I described, then time it to the engine, your mag drop will be lower and you will have a hotter spark. If I had a mag drop as high as 75, I would take the mag off and reset the points. When mine gets up near 60 I start to think about it. I prefer less than 50.
Checking the mag timing to the engine at the annual and finding a change, is telling you to reset the points timing within the mag. The mag itself hasn't moved in relation to the engine.

This is the process I use with mags, no matter who made them. They are all the same. All you need is a 1/2" wrench, a screw driver and a piece of paper.

If your fixing an impulse mag, be certain the fly weights are not engaged.
 
Pull the plug out of bottom of carb and flush some gas through. Main jet is probably partially blocked by water or debris.

Check oil screen

Check fuel screens in carb and in gascolator

And all the stuff others had mentioned.

The muffler being blocked you WILL notice a bigger change


Sent from my iPhone using SuperCub.Org
 
Also run a compression check when the engine is warm.
And it would be a good idea to check the accuracy of your tach.
How much calendar time is on the engine since overhaul?
 
Have you tried isopropyl alcohol or draining the carb bowl yet? I spent a lot of time and money chasing precisely what you describe only to find about 1/4 tsp of water in the carb. It doesn't go away by itself and it definitely interferes with high power setting fuel flows.
 
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You might have some corrosion but...like the others have suggested, fuel, ignition and compression must all be in place.
 
I have drained the carb but have not ran it yet. I have not seen any water in the sumps every and I sump before everything flight. but you never know!
 
Try leaning. My engine turns 2400 full rich in climb and will increase to 2550 when leaned. I know why mine runs rich(experimental). Anyway worth a try. (Of coarse beingf certified you would want to know why if you have a carb. issue)

Jack
 
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