Vibration while climbing

Chilito

Chilito

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Chilito
Recently I’ve noticed after an uneventful takeoff, full power, about 3000’ or so and climbing, my C150 begins to have a slight power hesitation. A bit of vibration that I can feel in the rudder peddles, and see on the RPM gauge—faint blips of lost rpms. As soon as I lower the nose back to level (or nearly level) flight and set cruise power, the engine runs completely normal. It makes climbs in an already slow airplane even less fun.

I want to believe it’s carb related, as in maybe a float level set too low that essentially chokes while in a nose high attitude, then finds enough fuel when we’re level again.

Thoughts appreciated.
 
Could be a lot of things. Does it do it with full power in level flight, is it related to engine temperature?
 
Chilito said:
Recently I’ve noticed after an uneventful takeoff, full power, about 3000’ or so and climbing, my C150 begins to have a slight power hesitatio
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While power issues (hesitation) can cause vibrations, induced drivetrain/aerodynamic vibrations usually dont cause power issues in recip aircraft. If that makes sense to you. But if this is a new problem you've noticed you may want to perform an indepth, hands on pre-flight just to make sure nothing has loosened up. Same with a tactile check of all your engine components with the cowl off.

Do you take off and climb at the same RPM?
Does your RPM change when you level off and the vibration stops?
What is your airspeed at take-off, climb, and when level off?
At what airspeed to you believe the vibration to start and stop?
Does the vibration suddenly appear or gradually appear?
 
Lean *a bit* at about 2000 MSL and see if the vibration still occurs around 3000 MSL.
 
Other factors include:

A bad mag. When were those mags last off for internal inspection? Supposed to be every 500 hours or so. Ignition is 90% of the engine's problems, usually, except (in the O-200) for the carb spider mount as noted in the link I posted earlier. The carburetor itself is what most people blame, and 90% of the time they're wrong. They spend money and time chasing it, to no avail.

A bad ignition harness.

Weak ignition can show up at full power, and settle down when the throttle is closed a bit. It sometimes doesn't show up in the runup mag checks.

Engine shockmounts shot, although that won't cause an RPM drop. In the climb the prop's downgoing blade is at a higher AoA, pulling the engine to the left, and worn mounts will let the engine's mounting lugs rattle on the mount bolts.

A leaking primer. That delivers extra fuel to the carb. Is the primer in and locked as per checklist? Checklists do mean something: there's a spring-loaded needle valve in the primer that closes off its outlet so the engine can't suck extra fuel though it, and locking the primer keeps that needle seated. An unlocked primer could cause an engine failure at low throttle settings, such as on approach, since low manifold pressures can suck a lot of fuel through it.

Once I sent in a brand-new carb for analysis, since the rest of the engine was freshly overhauled, had brand-new mags on it, and in the climb it shook until I closed the throttle a bit and saw it smooth out and gain some RPM. That was definitely a carb problem. One of the accelerator pump check ball springs was missing, and it was sucking extra fuel through the accelerator pump, fuel that ran up one side of the carb throat and overfuelled two cylinders. Closing the throttle plate a bit caused that stream to hit the plate and get atomized and dispersed more evenly.
 
There seems to be reasons for power loss and also for vibration.

Can’t come up with 1 cause for both.

You may want to check out Lycoming MSB 366 pertaining to

the Float Bowl Gasket. I know you have a TCM but there is likely the

same SB from the Carb people.

Quite common to have the bowl loosen which allows air in

the wrong place. Easy to check.

Don’t ignore the airframe regarding the vibration.

I’ve seen Strut Fairings resonate at certain engine speeds that

sounded like a machine gun.

Possibly the attitude when climbing may bring about the condition?
 
Thank you all for the responses! This has given me some good places to start. The carb, in particular, and mags.
 
Chilito said:
Thank you all for the responses! This has given me some good places to start. The carb, in particular, and mags.
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I bet it ain't the carb so much. It seldom is. Grab that carb airbox and try to move it side-to-side; it should move some. The whole airbox/carb/intake spider should be able to swing, stiffly, with the Lock-O-Seal washers and intake tube rubber hoses flexing. If it's rigid, there's at least one of your problems. There may be more.

And look at your logs to see when the mags were last done. There are a few of us here that remember our cars and pickups with points/condenser ignitions; those systems went away in the early or mid 1970s. It was standard practice to replace the points and condenser once a year or every 12,000 miles if you wanted to avoid trouble and get decent mileage. 12,000 miles at an average of 30 MPH is 400 hours. Your magnetos have those same points and condenser, and Bendix wants them checked at 400, Slick at 500, and yet most owners are running them to failure. Owners are used to electronic ignitions in their cars that almost never quit, but that experience cannot be applied to your airplane.
 
Dan Thomas said:
I bet it ain't the carb so much. It seldom is. Grab that carb airbox and try to move it side-to-side; it should move some. The whole airbox/carb/intake spider should be able to swing, stiffly, with the Lock-O-Seal washers and intake tube rubber hoses flexing. If it's rigid, there's at least one of your problems. There may be more.

And look at your logs to see when the mags were last done. There are a few of us here that remember our cars and pickups with points/condenser ignitions; those systems went away in the early or mid 1970s. It was standard practice to replace the points and condenser once a year or every 12,000 miles if you wanted to avoid trouble and get decent mileage. 12,000 miles at an average of 30 MPH is 400 hours. Your magnetos have those same points and condenser, and Bendix wants them checked at 400, Slick at 500, and yet most owners are running them to failure. Owners are used to electronic ignitions in their cars that almost never quit, but that experience cannot be applied to your airplane.
Click to expand...

Not to mention the possibility of a cracked distributor block, carbon tracking on said block, or worn points cam...
 
Another option considering he feels it in the pedals and sees it on the tach could be worn/loose engine mounts or some other item that gets out of sync especially since the vibration only starts during the climb and ends once leveled with no direct corrective input.
 
Broken engine mount? In addition to checking for loose and worn attachments, I suggest checking the steel mount itself with a bright light and a mirror for the hard to see areas. Also push and pull on the mount, or have someone else do this while inspecting. Cracked mounts can be very difficult to pinpoint, especially if they are dirty. Apply a slight amount of hand pressure on all components while inspecting. Look for obvious stuff like loose exhaust parts, anything that might have broken and now rubbing against the structure. Broken clamps, baffling, intake box, oil cooler, prop bulkhead. It doesn’t take much to set up a vibration.
 
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