cessna 150 carb troubles

bobkiksass

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bobkiksass
I have cessna 150, its a 1976 with a penn yann 0200 thats 10 yrs old w/ 300 hrs. About a month ago, a few times while flying the plane would randomly start vibrating and would loose a small amount of power when at wide open. Had this happen like 3 times, described situation to mechanic. We checked compression, all 78+ pulled plugs, everything seemed fine. He advised me that my prop needed to be overhauled, because it was rough and never had been done, I thought it was a good call. The mags also had a service bulletin, and had not been gone over 10 yrs so he thought we should have them overhauled.

I proceeded with the work on the prop, and mags. Got the plane back a few days ago, looking great, and sounding like it was "hitting" a lot better. Sounded smoother, he described that the mags were rough on the inside and this would make a big difference.

So I went to fly the plane, run up is great.... prop feels smoother, and the mag drop is hardly noticeable, much improved. I go to takeoff, give it wide open and only get 2400 rpm. I kinda climb like 20 ft, but realize this isnt right, so I put it back on the runway without going around.

Go to my mechanic, he suggests we try static power run, so we give it wide open now 2600-2650 rpm, way more power noticeably then when I just tried to takeoff. Im thinking how is this possible?

We pull the cowling, inspect everything. On the MA3SPA carb the throttle shaft was a bit sloppy from side to side when wide open. And a small amount of fuel could be seen leaking through the bushings on the sides of it when cycling the throttle. The shaft that activates the accelerator pump also had a considerable amount of slop. He seemed to think air could be leaking through the carb and was an issue. He was unsure if it explained the lack of full power on my attempted takeoff. He offered to let me remove the carb myself and so I did. He is going to send it to be inspected and repaired as necessary. It is one piece venturi ma3spa

I am hoping that it was the carb that caused this unexplained lack of power. It seems like everything else has been gone through. Only other thing Im thinking is to verify the induction system isnt leaking anywhere.

any insight on my 150 ?
 
I had a 150J with same carb. Found mine to have a bad accelerator pump check valve.
But with the excess motion in you throttle shaft, I would suspect that mabe sticking, and/or air getting through causing the troubles.

I'd give it a good cleaning, and IRAN it, and it should be fine. I wouldn't send it in for overhaul.
 
FWIW 26-2650 static sounds high. Maybe the whole problem is the tach? Carburetor problems are typically not intermittant. If it is running smoothly but shaking and short RPM check for a soft hydraulic unit. Charlie Melot Zephyr Engines
 
I've had two intermittent power problems. One was due to a foreign object in the inlet to the carb. It got sucked up into the carb intermittently. The other was due to internals in the muffler that had come apart and were intermittently restricting the muffler outlet.
 
Go to this thread and read posts 8 thru 14:

http://www.pilotsofamerica.com/forum/showthread.php?t=49482

This can show up on the takeoff roll more readily than with the brakes locked. The nosewheel is usually a bit unbalanced and can start the carb shaking and slopping fuel into the intake, and after that the engine's roughness keeps it up.

As for static runup RPM, here's what the TCDS specifies:

McCauley 1A102/OCM
Diameter: not over 69 in., not under 67 in.
Static rpm at maximum permissible throttle setting:
not over 2560, not under 2460
No additional tolerance permitted



Dan
 
Interesting, the mechanic was concerned with the throttle shaft vibrating side to side and how that would affect the butterfly moving inside the carb and affecting the airflow. There was considerable slop in the side to side movement of the throttle shaft and a bit forward and back allowing the butterfly to close off. From what youre explaining Dan, and what I read in the thread is that engine vibration can affect the performance of the carb. I would think even more so with that throttle shaft loose.

A few times I had experienced the motor start to vibrate and loose a bit of power while flying, it would last about 10-15 seconds and adjusting the power would usually stop it.

In your thread you reference an overhaul manual, is that information online ?

Thanks
Bob
 
Interesting, the mechanic was concerned with the throttle shaft vibrating side to side and how that would affect the butterfly moving inside the carb and affecting the airflow. There was considerable slop in the side to side movement of the throttle shaft and a bit forward and back allowing the butterfly to close off. From what youre explaining Dan, and what I read in the thread is that engine vibration can affect the performance of the carb. I would think even more so with that throttle shaft loose.

A few times I had experienced the motor start to vibrate and loose a bit of power while flying, it would last about 10-15 seconds and adjusting the power would usually stop it.

In your thread you reference an overhaul manual, is that information online ?

Thanks
Bob

TCM will provide you with online access to the manuals for your engine, you will need the MN and SN to sign up

Www.tcmlink.com
 
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