Cessna 150 vibration problem

[Policeboss]

Cessna 150 vibration problem.

Background. 1973 Cessna 150L recently purchased with approximately 1100 TSMO and 3900 TTAF. The plane was flown from Tennessee to Florida no problems. After owning for a couple months I had an annual a long list of items were replaced from wheel bearing,to carb heat box to ELT. New points were installed in the mags and the compression is good in all cylinders. My only complaint after having all the work done was the idle was set to low. I returned and the carb was adjusted and I was told that it needed a rebuild because of its age but that everything was working fine. The plane flew fine.
Just a few days after the carb adjustment (approx 10 hrs flight time) cruising at 6500ft and the engine sputters just enough to get your attention. Applied carb head and decided to descend as there was an airport below. After landing found that the plane would not run up past 1800rpm. After checking compression, plugs, timing, and rerouting my ignition wires it was determined that the carb needed replacement. A rebuilt marval carb was installed. I was told that the old carb accelerator pump was bad. The plane was back in business. However, on the return flight back home a vibration can be felt at cruise. At full throttle and during clime it may be there just not felt as much. But when in level flight and throttled to 2450 down to about 2200 you can feel a vibration.
I returned the plane to the first mechanic who checked the mags and the timing and adjusted the carb. It did not fix the problem. The very next day I took the plane to the second mechanic that installed the carb. They sent a third one up in the plane and he felt as there is nothing wrong with the engine that the wheel pants, something in the nose wheel or even motor mounts. This was determined after checking prop balance (without removal) and the fact that the vibration in his opinion can be felt in the rudder petals and that wind affecting the nose wheel that's attached the the petals could be causing the vibration. Was sent home (no charge) and advised to remove the wheel pants and see if that corrects the problem. I'm planning to do that tomorrow. However wouldn't that have been an issue before.

My question is has anyone else experience anything like this before? I'm sure that there are more things that have been checked that I have not listed. Any advise would be greatly appreciated. Thanks in advance. My gut feeling is that my vibration is carb related. So for such a long post.

 

[N801BH]

First...Welcome to POA...

If the prop was removed during the annual my guess is it was reinstalled different then before... Move it 60 degrees and see what happens.. As for the bad carb... the old carb accelerator pump at cruise will not cause that vibration..

 

[Policeboss]

Ben thanks for the quick reply. Maybe my post was not clear enough. After annual plane was smooth running. Vibration began after new carb installed. But when I took it back to that shop. Their guy said my vibration is not engine.

 

[Tom-D]

Cessna 150 vibration problem.

Background. 1973 Cessna 150L recently purchased with approximately 1100 TSMO and 3900 TTAF. The plane was flown from Tennessee to Florida no problems. After owning for a couple months I had an annual a long list of items were replaced from wheel bearing,to carb heat box to ELT. New points were installed in the mags and the compression is good in all cylinders. My only complaint after having all the work done was the idle was set to low. I returned and the carb was adjusted and I was told that it needed a rebuild because of its age but that everything was working fine. The plane flew fine.
Just a few days after the carb adjustment (approx 10 hrs flight time) cruising at 6500ft and the engine sputters just enough to get your attention. Applied carb head and decided to descend as there was an airport below. After landing found that the plane would not run up past 1800rpm. After checking compression, plugs, timing, and rerouting my ignition wires it was determined that the carb needed replacement. A rebuilt marval carb was installed. I was told that the old carb accelerator pump was bad. The plane was back in business. However, on the return flight back home a vibration can be felt at cruise. At full throttle and during clime it may be there just not felt as much. But when in level flight and throttled to 2450 down to about 2200 you can feel a vibration.
I returned the plane to the first mechanic who checked the mags and the timing and adjusted the carb. It did not fix the problem. The very next day I took the plane to the second mechanic that installed the carb. They sent a third one up in the plane and he felt as there is nothing wrong with the engine that the wheel pants, something in the nose wheel or even motor mounts. This was determined after checking prop balance (without removal) and the fact that the vibration in his opinion can be felt in the rudder petals and that wind affecting the nose wheel that's attached the the petals could be causing the vibration. Was sent home (no charge) and advised to remove the wheel pants and see if that corrects the problem. I'm planning to do that tomorrow. However wouldn't that have been an issue before.

My question is has anyone else experience anything like this before? I'm sure that there are more things that have been checked that I have not listed. Any advise would be greatly appreciated. Thanks in advance. My gut feeling is that my vibration is carb related. So for such a long post.

This is very typical of the new rebuilt carbs from Kelly Aerospace.

You Never ever overhaul a Marvel Carb, your accelerator pump is a $110.00 fix.

 

[Policeboss]

Tom thanks. I know the carb came from somewhere in California will have to check to find out. They sent my old carb back as an exchange so I'm stuck with what I have. Not sure what I should do next.

 

[Tom-D]

Tom thanks. I know the carb came from somewhere in California will have to check to find out. They sent my old carb back as an exchange so I'm stuck with what I have. Not sure what I should do next.

watch E-bay, buy a unmolested MA3 SPA P/N (for your aircraft) send it to me.

I'll clean, inspect and repair as necessary and return. it must have a 2 piece Venturi, metal float, and old style atomizer nozzle.

read all the old ADs on the Marvel MA3 carbs, when precision air-motive lawyers started to sell parts thru the FAA's AD system they really messed it up. Kelly has always made all the parts for the carb, but they did not follow the old design, they placed plastic floats, 1 piece Venturi and a different atomizer nozzle, now it runs rich, and stutters like it is burning too much fuel. which it is, the old carbs would give 6.5-7.5 gallons per hours, the new ones get 8-9 gallons per hour, foul plugs and run rough.

 

[somorris]

So Tom, it sounds like the vibration is actually a miss in the engine caused by too much fuel getting to the cylinders? Interesting.

 

[Tom-D]

So Tom, it sounds like the vibration is actually a miss in the engine caused by too much fuel getting to the cylinders? Interesting.

Pull your good running carb off and put a new kelly on, prove it to your self.

 

[Policeboss]

Tom is there anything I can do with the existing carb? Less throw it in the trash! I was actually thinking that it was too lean, not rich.
MA 3spa
Serial # BE 27 24008
Part # 10-4894-1
Code # KA D 12099
?? V 92 FAA PMA

 

[Tom-D]

Tom is there anything I can do with the existing carb?

Simply keep sending it back as not working.

until they get it right.

they can adjust the air bleed metering jet.

 

[Tom-D]

can you post a picture of your carb's data tag?

 

[steingar]

My 50 ate a valve once, the resulting vibration certainly got my attention. But you would think a decent mechanic would notice that.

 

[trcsmith]

Tom is there anything I can do with the existing carb? Less throw it in the trash! I was actually thinking that it was too lean, not rich.
MA 3spa
Serial # BE 27 24008
Part # 10-4894-1
Code # KA D 12099
?? V 92 FAA PMA

Send it back like Tom said. If it was installed correctly with no vacuum leaks it should have run fine. Something could have not been installed correctly inside.. To blame it on wheel pants is to get rid of you. But if the plane was flying good before carb change and the nose was not messed with... CARB!

 

[Dan Thomas]

Send it back like Tom said. If it was installed correctly with no vacuum leaks it should have run fine. Something could have not been installed correctly inside.. To blame it on wheel pants is to get rid of you. But if the plane was flying good before carb change and the nose was not messed with... CARB!

The mags were also messed with, though one would have to be bad indeed to limit full RPM to 1800 on the ground.

90% of engine hassle are electrical, but Tom is right about these silly carbs. Before all the ADs they worked well enough, but just try to find the old, removed parts (two-piece venturi and fuel nozzle) to put it back the way it should be, which is allowed by the last revision to the final venturi/nozzle AD as long as the venturi is checked for looseness every 100 hours. Those parts are all gone and we're stuck with the "new and improved" junk.

Dan

 

[John221us]

I have been chasing a similar problem on my Cherokee (O-320-E2A). Kelly did screw up my carb, but I have been through another rebuild from an engine shop and also a loaner (known good) carb since then and my problem has not resolved. My EGT rises (#4 cylinder probe) and we moved it to #2 and it rises there too, so I seem to be lean. Everyone says this is induction leak, but we haven't found that yet and I have been chasing this for a couple of months. I am rough between 2300 and 2450 RPMs.

 

[Policeboss]

 

[Policeboss]

This is the old carb

 

[Policeboss]

What the plugs look like.

 

[Tom-D]

can you see the different part numbers?

what is your average fuel burn rate ?

the old black label carb was a much better carb than the red label.

 

[Tom-D]

Be certain the carb spider is mounted to the case with the proper mounting hardware. (see the IPB) and is not ridged. When the engine can shake the carb, it will alter the float level setting and the carb will not run correctly.

 

[Policeboss]

I spent some time yesterday and today looking for anything else that might be a problem.I totally agree with Tom that's it's a carb issue. So adjusted the carb mixture about 1/2 turn then 1/4 turn each time taking it up and flying the pattern at 1000ft. My vibration seemed to get a little better. But still not right. Going to call the guys that installed it tomorrow and see if thy can do anything else.

 

[Tom-D]

I spent some time yesterday and today looking for anything else that might be a problem.I totally agree with Tom that's it's a carb issue. So adjusted the carb mixture about 1/2 turn then 1/4 turn each time taking it up and flying the pattern at 1000ft. My vibration seemed to get a little better. But still not right. Going to call the guys that installed it tomorrow and see if thy can do anything else.

Did you turn the big knob on the back of the carb?

that is only the idle mixture air bleed adjustment. and does not effect the cruise mixture, that is set by either the cruise metering jet or the mixture control.

 

[Policeboss]

Yes that is the one I turned. Today at 3000ft At cruise you can pull the mixture out 10 clicks with no change on the 11 click and 12 click the engine shakes more. Push it back in two two clicks back to the same. No change. On the ground 18 clicks to full lean cut off

 

[Tom-D]

The method to use when adjusting the idle mixture is:

run the engine on the ground at idle until it is warm.
pull the mixture out fully. watch the tach. it should rise 10-50 RPM as the engine dies.

the big knob has two arrows one says lean, the other says rich, (R--><--L)

if the RPM rises over 50 turn 1/4 turn to L
If the RPM does not rise, turn it 1/4 turn to R

repeat as required to get it right.

 

[Policeboss]

 

[Policeboss]

 

[Tom-D]

http://i1325.photobucket.com/albums...ED302BD8-162-000000098EE5FEBC_zpsc78c5737.jpg


Tom if I can come up with an agreeable price with this seller would this be what I need

Should be, but you can't tell what is inside until you open it up.

 

[Policeboss]

 

[Policeboss]

Can you tell from the pic if it's a one or two piece?

 

[Tom-D]

Can you tell from the pic if it's a one or two piece?

no...

 

[Dan Thomas]

Looks like a two-piece venturi. See the little flat tabs on the three legs on the secondary venturi? They're clamped under the primary venturi, and are what get loose or break off and let the secondary get sucked into the engine or screw up the airflow, hence the AD. Checking that for tightness every 100 hours is the alternative permitted by the revision to the AD.

Dan

 

[Tom-D]

Looks like a two-piece venturi. See the little flat tabs on the three legs on the secondary venturi? They're clamped under the primary venturi, and are what get loose or break off and let the secondary get sucked into the engine or screw up the airflow, hence the AD. Checking that for tightness every 100 hours is the alternative permitted by the revision to the AD.

Dan

Are you sure enough to bet his money on it?

 

[N801BH]

Are you sure enough to bet his money on it?

I feel real bad for the OP, as he has already bet his hard earned money on a FAA certified carb, only to find out by several FAA certified A&P /IA's that Kelly produces junk, and that fact is well know throughout the inner circle of mechanics and for some reason no one is giving the FAA the feedback I thought A&P's were bound by law to provide..

 

[Tom-D]

I feel real bad for the OP, as he has already bet his hard earned money on a FAA certified carb, only to find out by several FAA certified A&P /IA's that Kelly produces junk, and that fact is well know throughout the inner circle of mechanics and for some reason no one is giving the FAA the feedback I thought A&P's were bound by law to provide..

How much time and money do you believe I spent fighting the ADs that started all this? we did end up getting the AD re-written to allow the carbs to be returned to their original condition with the 100 hour inspections.

other wise you push too hard they simply stop supporting the carbs

 

[N801BH]

How much time and money do you believe I spent fighting the ADs that started all this? we did end up getting the AD re-written to allow the carbs to be returned to their original condition with the 100 hour inspections.

other wise you push too hard they simply stop supporting the carbs

I am right with you here Tom...... A half century ago Marvel designed and manufactured a VERY simple and basic carb.. it is soooooo crude, just look closely at the castings the OP posted. I took a sand casting class in 8th grade and my instructor would have given me an F for the test and made me melt down anything that looked that bad..

The way the FAA has rules set up, it would be next to impossible to manufacture a billet one today that is far superior as the costs are prohibitive to get the FAA to bless it... And it appears Kelly is riding that technicality all the way to the bank...

 

[Tom-D]

I feel real bad for the OP,

I feel bad for the whole industry, every time we have a carb problem the local A&P replaces a good carb with a POS from Kelly, when in reality they should repair the one they have.

There is only one moving part in the carb that wears, that is the throttle shaft bushing, they are .35 cents per pair at your local hardware store.

But we have a new crop of vocational school educated A&Ps that have been taught to not accept any liability that comes with repairing any component.

Combined with the FBOs that can mark up the price of a $700 part enough to help pay the overhead.

So, it's not just the FAA that is causing this to happen.

way back in 1994 when Precision Airmotive bought the production certificate for the MA series carbs they discovered 7 failures in 37 years of service for that carb, they used that information to gain a safety AD from SEA FSDO. That AD required all 2 piece venturis to be replaced with in the next 100 hours of operation, we protested that on the bases that there were not enough single piece venturis to allow that to happen. and got a reprieve on the 100 hours. When the single piece venturi went into service we found it ran really bad, rather than back stepping and redesigning the venturi, they produced a new atomizer nozzle to cure the problem. that did not work either.
They then got sued and lost a multi million dollar settlement.

After the dust settled on that, Precision sold the production certificate to Kelly, Who by the way was manufacturing all the parts for Precision all during this evolution. now Kelly ownes the PMA and the Production certificate and can pretty much do as they well please.

 

[Dan Thomas]

After the dust settled on that, Precision sold the production certificate to Kelly, Who by the way was manufacturing all the parts for Precision all during this evolution. now Kelly ownes the PMA and the Production certificate and can pretty much do as they well please.

I thought it was Tempest that bought the production rights. I think Kelly just remanufactures them. And they don't do that well.

http://www.generalaviationnews.com/2010/09/01/marvel-schebler-name-returns-for-carburetors/

Avstar is also making knockoffs but they look a lot better. Very pricey. They're milled from 60601-T6, not cast aluminum.

Tempest is upset about them:
http://msacarbs.com/pdf/SB-16_O 081210.pdf


Dan

 

[Tom-D]

I thought it was Tempest that bought the production rights. I think Kelly just remanufactures them. And they don't do that well.

http://www.generalaviationnews.com/2010/09/01/marvel-schebler-name-returns-for-carburetors/

Avstar is also making knockoffs but they look a lot better. Very pricey. They're milled from 60601-T6, not cast aluminum.

Tempest is upset about them:
http://msacarbs.com/pdf/SB-16_O 081210.pdf


Dan

Yes Tempest now has the production certificate, I do not know how that transpired.

And I have no experience with the Tempest carbs.

 

[N801BH]

If it works half as good as it looks then the carb problem is cured......

God only knows what it costs though..

 

[Dan Thomas]

If it works half as good as it looks then the carb problem is cured......

God only knows what is costs though..

A few years ago we bought a Lyc factory reman O-540 for the 182RG. The carb that came with it didn't atomize the fuel properly and at any RPM two cylinders were cold, and at idle those two wouldn't even fire. Far too rich. Lyc had Avstar send us another carb, which we were billed for until they processed the old one for warranty credit; the bill for the carb (an HA-6) was $8800.

Not eighty-eight dollars. Eighty-eight hundred. For a carburetor.

My whole airplane is probably worth less than that.

Dan