Why I'll never buy another Marvel-Schebler carb

I'm a bit confused here. Why did moving to a place that is 4600 feet cause this problem to manifest itself? Did no one ever take that 150 over 4600 feet before?

As for the folks at Marvel Schebler, they have been far too busy writing service bulletins (like their predecesors at Volare and Precision Airmotive) to deal with whining customers. This poor little carburetor must hold the record for the shear tonnage of service documents written over it.
 
Silvaire said:
I'm a bit confused here. Why did moving to a place that is 4600 feet cause this problem to manifest itself? Did no one ever take that 150 over 4600 feet before?
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Not enough to recognize the problem, apparently -- or they would have fixed it!

According to the logs, it spent the last 20 years at airports within a few feet of sea level, outside of metropolitan areas, and most flights were local. If they got up to 4500 feet, they probably just adjusted the mixture and assumed that the rich running was normal. At that altitude AGL, the crummy power isn't as easy to notice as it is when you're taking off at 4600 MSL and the engine is flooding as you're trying to get over the obstacle off the end of the runway.
 
What obligation would Marvel-Shebler Aircraft Carburetors, LLC, an entity formed in 2008 have to honor a promise made by Precision Airmotive, LLC 20 years ago ?

Whoever owned the plane at the time goofed and didn't request the 'fix' kit. Try to get your $160 from that guy or his mechanic.

I am just glad someone is still willing to assume the liability that comes with making fuel system components for little old airplanes. Any screw or bolt you send out could result in a 110mil verdict against you in a Philadelphia courtroom.
 
denverpilot said:
Agreed they screwed up a fine carb for a lack of proper inspections. Put the two-piece back in.

If $160 is tight and you own multiple aircraft, it's time to sell one. Seriously.
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And he's building another......


That letter from Marvel was not very professional, but honestly pay the damn money and fix your plane.. OR try to find the part on barnstormers or something for less.

I think for the time you waste hitting your head against the wall for $160, it's kinda silly
 
Good thing he doesn't own a Lycoming IO-540 with a blacklisted crank :rolleyes2:
 
NineThreeKilo said:
And he's building another......


That letter from Marvel was not very professional, but honestly pay the damn money and fix your plane.. OR try to find the part on barnstormers or something for less.

I think for the time you waste hitting your head against the wall for $160, it's kinda silly
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Actually, I'm building several others. All of those are on hold. Fortunately, I hadn't reached the buy-carbs stage on any of them, so can drop the idea of buying MS.

As far as the nozzle, what I'm going to do is find an example to look at, then make the part. I'm guessing that I can modify the one that doesn't work. In fact, I can probably improve on their design -- I don't imagine that they did anything more than the minimal engineering or testing. If so, I can sell the superior nozzle cheap enough to make it worth guys buying them. A look in the Maintenance forum here shows that I'm far from the only one around who is less than inspired by MS' slipshod engineering.
 
NineThreeKilo said:
And he's building another......


That letter from Marvel was not very professional, but honestly pay the damn money and fix your plane.. OR try to find the part on barnstormers or something for less.

I think for the time you waste hitting your head against the wall for $160, it's kinda silly
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I don't fault him for trying. But it's water long under the bridge back when the common man's airplane wasn't an antique or an experimental, and manufacturers had things in stock because they had deadlines to ship a couple hundred to Cessna.
 
SoloEqs said:
Actually, I'm building several others. All of those are on hold. Fortunately, I hadn't reached the buy-carbs stage on any of them, so can drop the idea of buying MS.

As far as the nozzle, what I'm going to do is find an example to look at, then make the part. I'm guessing that I can modify the one that doesn't work. In fact, I can probably improve on their design -- I don't imagine that they did anything more than the minimal engineering or testing. If so, I can sell the superior nozzle cheap enough to make it worth guys buying them. A look in the Maintenance forum here shows that I'm far from the only one around who is less than inspired by MS' slipshod engineering.
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I wouldn't go messing with the nozzle. When MS drilled it, they created other problems. That nozzle angles upward into the secondary venturi and discharges approximately into the center of it. Drilling holes in it lets fuel out farther down toward the carb wall and lets extra fuel flow up the back of the manifold and into the rear cylinders. Now we have some cylinders richer than the others and even more roughness.

Dan
 
I have to do SOMETHING. I've got hills and other obstacles right off the end of the runway, and a rough running engine doesn't give me a whole lot of confidence that I'll get over them. I've got the mixture pulled way out to find the smooth spot (relatively speaking).
 
You folks simply don't know the history of this problem,,
Marvel has been out of business since the early 90's Precision Airmotive of Marysville Wa. bought the production of a very good carb, that had 7 failures to loose venturis.
Precision lawyers used these failures to gain a emergent safety AD from SEA FSDO, to change to a 1 piece venturi, to sell parts thur the ADs system, which cause all the carb that were modified to run rich.
When this was discovered by SEA FSDO the AD was changed to read the 1 piece could be kept and inspected every 100 hours or annual which ever occurred first.

Precision then came up with a new fuel nozzle which made matters worse, and then sold the production certificate to Kelly, who holds it now.

the funniest portion of this is, Kelly has manufactured all the parts for this carb since the 80's .

and they except no part of the responsibility for any of the problem.
 
Tom-D said:
You folks simply don't know the history of this problem,,
Marvel has been out of business since the early 90's Precision Airmotive of Marysville Wa. bought the production of a very good carb, that had 7 failures to loose venturis.
Precision lawyers used these failures to gain a emergent safety AD from SEA FSDO, to change to a 1 piece venturi, to sell parts thur the ADs system, which cause all the carb that were modified to run rich.
When this was discovered by SEA FSDO the AD was changed to read the 1 piece could be kept and inspected every 100 hours or annual which ever occurred first.

Precision then came up with a new fuel nozzle which made matters worse, and then sold the production certificate to Kelly, who holds it now.

the funniest portion of this is, Kelly has manufactured all the parts for this carb since the 80's .

and they except no part of the responsibility for any of the problem.
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FSDO's cannot and have never issued Airworthiness Directives. The FSDO can submit it's findings through Region and on to the appropriate Directorate for analysis and then a process is followed for the final submission of the AD. An emergency AD can be expedited, but again it follows a process well above the FSDO level.
 
It sucks to have an airplane and be broke. That is about all that I see going on here. I know that it sucks because I am in the same boat, so to speak. Except I need about three AMU's to get in the air again. Plus an annual.
 
RotorAndWing said:
FSDO's cannot and have never issued Airworthiness Directives. The FSDO can submit it's findings through Region and on to the appropriate Directorate for analysis and then a process is followed for the final submission of the AD. An emergency AD can be expedited, but again it follows a process well above the FSDO level.
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what ever, Precision got the ADs
 
SoloEqs said:
If they're making parts to someone else's specifications, it's not their fault.
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Then why haven't they fixed the problem? they own it now, and have for several years.
 
alfadog said:
It sucks to have an airplane and be broke. That is about all that I see going on here. I know that it sucks because I am in the same boat, so to speak. Except I need about three AMU's to get in the air again. Plus an annual.
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It sucks more to have SEVERAL airplanes and be broke! ;)

It sucks EXPONENTIALLY more to have several airplanes, LIVE AT AN AIRPORT and be broke! :(
 
SoloEqs said:
It sucks more to have SEVERAL airplanes and be broke! ;)

It sucks EXPONENTIALLY more to have several airplanes, LIVE AT AN AIRPORT and be broke! :(
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My sympathies. Though I would not mind it so much if I lived at an airport and had hangar space to play around in.
 
Tom-D said:
Then why haven't they fixed the problem? they own it now, and have for several years.
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Are they only making the parts for Tempest, or do they actually own the design now?

If they're just contract manufacturing, they can't change anything. Whoever owns the design is responsible.

As you see, the MS people aren't willing to spend $10 to solve the problem on an individual basis, who would expect them to spend the money to correct a design flaw?
 
alfadog said:
My sympathies. Though I would not mind it so much if I lived at an airport and had hangar space to play around in.
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It has its moments. :wink2:

For one thing, being out of work has given me time to do some tinkering, and an incentive to save money. For instance, I bought a $10 Steelcase-type desk at a thrift store, mounted it on some big cart wheels that were in the junkpile here, and now have a great push-around workbench with big drawers holding the tools and stuff that I'm always using. I paid $5 each for a couple of bigger desks which are against the wall and have my big toolboxes on them

I also found one of those adjustable-height tables that they use with hospital beds, and use that as a mobile worktable.

Right now, there's a bunch of stuff in the hangar that I want to get rid of, but we're having a rummage sale here next weekend, so I'm hoping to get more space and more cash.
 
SoloEqs said:
Are they only making the parts for Tempest, or do they actually own the design now?

If they're just contract manufacturing, they can't change anything. Whoever owns the design is responsible.

As you see, the MS people aren't willing to spend $10 to solve the problem on an individual basis, who would expect them to spend the money to correct a design flaw?
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There was no design flaw, that design worked the 30's-90's with 7 failures due to a loose venturi.

It was all Lawyers at Precision who started this mess, just to sell parts. and get business for the company.
 
Tom-D said:
There was no design flaw, that design worked the 30's-90's with 7 failures due to a loose venturi.

It was all Lawyers at Precision who started this mess, just to sell parts. and get business for the company.
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The flaw I'm talking about is the 1-piece venturi, which obviously wasn't tested to the same level that they would have to test an STC.
 
SoloEqs said:
The flaw I'm talking about is the 1-piece venturi, which obviously wasn't tested to the same level that they would have to test an STC.
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true..
 
SoloEqs said:
I'm seeing things online to indicate that the MA-4 uses the same venturi as the MA-3, any idea if this is true? I may have a line on a 2-piece venturi from an MA-4.
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the 4 is bigger
 
SoloEqs said:
I have to do SOMETHING. I've got hills and other obstacles right off the end of the runway, and a rough running engine doesn't give me a whole lot of confidence that I'll get over them. I've got the mixture pulled way out to find the smooth spot (relatively speaking).
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Before you drill that thing and maybe make it worse, make sure that the carb spider is mounted correctly. Maybe some mechanic has found it "loose" and "fixed" it.

See this thread for details:

http://www.pilotsofamerica.com/forum/showthread.php?t=49482&highlight=lock-o-seal+washer

Dan
 
Tom-D said:
Do you really want to put modified parts in your carb?
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If the venturi is the same part number for both MA-3 and -4, it's not a modified part, and putting in the original parts should restore original performance.

If the original part is unobtainable, I would be willing to shape the current part to meet the profile of the original part that worked.

Likewise, if the "pepperbox" nozzle is an improvement over the original, and the only difference is a couple of holes in it, yes, I would happily drill those holes to duplicate the factory nozzle.

There is no more risk to doing these things than to using the original part, if the modification work duplicates the configuration of the original, which is why the FARs permit owners to make their own parts.
 
Dan Thomas said:
Before you drill that thing and maybe make it worse, make sure that the carb spider is mounted correctly. Maybe some mechanic has found it "loose" and "fixed" it.

See this thread for details:

http://www.pilotsofamerica.com/forum/showthread.php?t=49482&highlight=lock-o-seal+washer

Dan
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Thanks, Dan! Yes, I knew about it, but it never hurts to remind people.

Anyone in the future who wonders about the reference, the intake spider is supposed to be isolated from the engine with a rubber washer between the engine and the spider, and another between spider and the castellated nut, which is only supposed to be finger-tight.

Vibration from the engine, especially at high RPM, can make the fuel float bounce (think "whitecaps" in the fuel bowl), which makes the float valve open more than it should, thus encouraging flooding.

The Continental manual (and everyone who uses them) calls them "Lock-O-Seal" washers (P/N 538556 -- Figure 12, Part -1 in the March 1973 parts book) but the Genuine Aircraft Hardware page says that Lock-O-Seals are for hydraulic fittings, and the ones we need are Stat-O-Seals. Whatever you want to call them, the ones to use are for AN6 (3/8") studs. http://www.gen-aircraft-hardware.com/stat-o-seal.asp

Note: These seals are designed to make a gastight seal around a bolt, when cinched down to make metal-to-metal-to-metal contact. If you make metal-to-metal contact on either side, you have defeated the purpose of putting them in there. The only reason to use these instead of just rubber is because the metal provides a retainer for the rubber inside, but make sure you don't crank them tight. Properly done, you can take a VOM and get no electrical continuity between the stud and the carb.
 
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The correct carb configuration is :

metal float (brass), metal needle valve, 2 piece venturi, leather accelerator pump.

plus the proper size jets for your engine.

or buy a new tempest carb.
 
Tom-D said:
Big If…
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Yep. That's why I want to see the parts lists for both carbs.

However, the MA-4SPA is pretty much the same carb as the MA-3SPA, the only obvious difference is the flange size, and they stepped the bore up above the venturi, so there's a good strong possibility that they're the same below that point.
 
Tom-D said:
The correct carb configuration is :

metal float (brass), metal needle valve, 2 piece venturi, leather accelerator pump.

plus the proper size jets for your engine.

or buy a new tempest carb.
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The chance of me ever buying another anything from Tempest that's more complex than a spark plug or oil filter is really, really, REALLY low.

If I ever need an accelerator pump or float valve, I'll buy them from AvStar.
 
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