Carb options

stingray

stingray

Line Up and Wait
Joined
Jan 15, 2007
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671
Location
Grantsburg WI
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Display name:
Daniel Michaels
I have a Taylorcraft with an A65 Stromberg carb no mixture control.

It has the steel needle and leaks a little. I just rebuilt it and tried to seat the needle better, worked some. Problem is the last owner must have stripped out the screen plug so it leaks there also. I have another Stromberg off of a C-85 that I could make work by using the parts from the A65 carb.

I wanted to use AV Mogas mix so I was trying to stay with the steel needle. I also am going to put the C-85 in another Taylorcraft.

Should I Fix up one of the Strombergs for the A65 and look for a Marvel-Schebler for the C85? Or Just look for 2 Marvel-Scheblers for both?

I don't remember hearing about the Marvel carbs leaking and I like the positive mixture control.

Dan
 
stingray said:
I have a Taylorcraft with an A65 Stromberg carb no mixture control.

It has the steel needle and leaks a little. I just rebuilt it and tried to seat the needle better, worked some. Problem is the last owner must have stripped out the screen plug so it leaks there also. I have another Stromberg off of a C-85 that I could make work by using the parts from the A65 carb.

I wanted to use AV Mogas mix so I was trying to stay with the steel needle. I also am going to put the C-85 in another Taylorcraft.

Should I Fix up one of the Strombergs for the A65 and look for a Marvel-Schebler for the C85? Or Just look for 2 Marvel-Scheblers for both?

I don't remember hearing about the Marvel carbs leaking and I like the positive mixture control.

Dan
Click to expand...

Fix up that Stromberg. I have one on my A65 and I work on the Marvel Scheblers (which some techs call the Marvellous Dribblers) as part of my job. The Stromberg is superior, in my view.

The Stromberg has no accelerator pump (it has an accelerator well and doesn't really miss the pump), and its mixture control is a back-suction affair that you can't use to kill the engine. Other than that, its fuel distribution into the airflow is far better than the MS carb (which tends to spray it toward the back, making the rear cylinders run richer), it doesn't suffer loose venturis like the MS did before the AD. (The AD required a venturi change that then made the engine run rough, so an AD amendment made a change to the fuel nozzle in some carbs, which made fuel distribution terrible and more roughness, and another AD amendment allowed the old venturis and nozzles to go back in, inspected every 100 hours. If you could find old venturis. We couldn't. They were all returned to the factory and destroyed. The new venturis have squared-off support legs that cause turbulence and poor performance. Just like a squared-off, flat leading edge.) The Stromberg can be violently shaken without spilling fuel from the bowl vent into the carb throat like the MS does, where it makes the engine run like a toilet on acceleration. The torsional vibration of the engine does it, and the O-200 with its softer mounts moved so much and caused the carb to flood the engine, so then the carb spider had to be mounted on the case studs using "Lock-O-Seal" washers and finger-tight castellated nuts to let it flex, with the intake tube rubber sleeves allowing flexing as well.

Here's the AD on the venturi/nozzle debacle:
http://rgl.faa.gov/Regulatory_and_Guidance_Library%5CrgAD.nsf/0/9F87A5E42C10900C86256A410065C0CD?OpenDocument

Something like $900 for an MS MA4 carb. And it doesn't work well at all. Their HA-6 carbs are about as bad. Precision sold the line to Tempest last spring, and I hope Tempest reworks the whole lineup and comes up with carbs that work. Shoot, a five-dollar junkyard Volkwagen carb works better than these things.

Dan
 
stingray said:
I have a Taylorcraft with an A65 Stromberg carb no mixture control.

It has the steel needle and leaks a little. I just rebuilt it and tried to seat the needle better, worked some. Problem is the last owner must have stripped out the screen plug so it leaks there also. I have another Stromberg off of a C-85 that I could make work by using the parts from the A65 carb.

I wanted to use AV Mogas mix so I was trying to stay with the steel needle. I also am going to put the C-85 in another Taylorcraft.

Should I Fix up one of the Strombergs for the A65 and look for a Marvel-Schebler for the C85? Or Just look for 2 Marvel-Scheblers for both?

I don't remember hearing about the Marvel carbs leaking and I like the positive mixture control.

Dan
Click to expand...

Find an old marvel (salvage yard) and send it to me, I'll repair as required and it will work just fine on your 65 & 85. last one I did was under 200 bucks like new.

I have no problems repairing them.
 
NC19143 said:
Find an old marvel (salvage yard) and send it to me, I'll repair as required and it will work just fine on your 65 & 85. last one I did was under 200 bucks like new.

I have no problems repairing them.
Click to expand...

Tom, does the MS carb have a mixture control (that works)?
 
NC19143 said:
Find an old marvel (salvage yard) and send it to me, I'll repair as required and it will work just fine on your 65 & 85. last one I did was under 200 bucks like new.

I have no problems repairing them.
Click to expand...

I'm looking I,m looking!

Dan
 
For more information on Stromberg carbs, see the information Neal Wright has written. It's on the Fly Baby Engine page, under "Technical Help" not far from the top.

Ron Wanttaja
 
stingray said:
Lance I had found this, http://www.cessna120-140.org/forum/viewtopic.php?t=2418 It explained it a little better as far as the mixture control goes.

Dan
Click to expand...

Good article. I had no mixture control on mine at all; many were made this way with just a cover plate over the valve cavity and no parts inside. Full rich all the time. I could not find the parts so made them myself (was a machinist in a former life) and instead of drilling those tiny, tiny holes in the top valve plate (I had no drills that small) I chucked the plate a little cocked in the lathe and cut a small, ramped v-bottomed arc from the one large hole I had drilled. Turned the chuck by hand, of course, since it only needed to turn about 60 degrees. With the v-groove against the bottom valve plate, it's full rich when the two holes are lined up and starts to lean the engine when the sloped groove shallows out and restricts the flow of ambient air into the venturi's port. Same effect as the decreasing hole sizes.

The Marvel Schebler carb uses a rotary valve in the bottom of the bowl that controls fuel flow itself. It's the one respectable aspect of that carb (in my opinion; others may disagree) and it works well. It has two small cylinders, one inside the other, and both have notches cut into their walls. When the notches are lined up fuel flows easily into the center of the assembly and to the nozzles. As the inner cylinder is turned when the mixture control is pulled, the net notch width gets narrower and fuel flow is restricted. Idle cutoff is at total notch occlusion.

See it at the bottom of this page:

http://www.kellyaerospace.com/articles/Accessory_AMT.pdf

Dan
 
stingray said:
I'm looking I,m looking!

Dan
Click to expand...

From this forum: http://mail.westmont.edu/pipermail/aeronca/2006-June/068302.html

I see this:

"To use the Marvel Schebler carburetor in place of the Stromberg carburetor
you will need to modify the top of your carburetor air box. The problem is
due to the pump inlet check valve and inlet screen housing being below the
bottom plane of the carburetor. Therefore you will need to dish out that
area so there is no interference between the two. Probably your throttle
cable will also have to be changed since the lever arms are located on
opposite sides of the carburetors. All this work has to be documented on a
FAA 337 form and signed by your AI.

"My vote is to have the Stromberg overhauled. On the otherhand, I do have a
spare MS 10-4233 available for only $4000.00. Will trade for a flying 7AC
though. (Grin) Might be cheaper to order a new one from Precision Air
Motive though if you insist on going in that direction."

End of quote.

And from a little farther up that thread, where the fellow is looking for an MS carb to replace the Stromberg/Bendix:

"So what is gold selling for these days. That carb costs more per pound than
gold. It might be better but I have heard that it is about the same as a
Bendix IF you can get it to run your engine correctly. Those that have them
call them Marvelous Dribblers. They have their own set of quirks. You do
get a real mixture control so you can lean it out as the float sinks from
either cracks in the metal float or gas absorbing plastic float. Either
carb works very well until some thing wears."

Something to consider.

Dan
 
Last edited:
Dan Thomas said:
Good article. I had no mixture control on mine at all; many were made this way with just a cover plate over the valve cavity and no parts inside. Full rich all the time. I could not find the parts so made them myself (was a machinist in a former life) and instead of drilling those tiny, tiny holes in the top valve plate (I had no drills that small) I chucked the plate a little cocked in the lathe and cut a small, ramped v-bottomed arc from the one large hole I had drilled. Turned the chuck by hand, of course, since it only needed to turn about 60 degrees. With the v-groove against the bottom valve plate, it's full rich when the two holes are lined up and starts to lean the engine when the sloped groove shallows out and restricts the flow of ambient air into the venturi's port. Same effect as the decreasing hole sizes.

The Marvel Schebler carb uses a rotary valve in the bottom of the bowl that controls fuel flow itself. It's the one respectable aspect of that carb (in my opinion; others may disagree) and it works well. It has two small cylinders, one inside the other, and both have notches cut into their walls. When the notches are lined up fuel flows easily into the center of the assembly and to the nozzles. As the inner cylinder is turned when the mixture control is pulled, the net notch width gets narrower and fuel flow is restricted. Idle cutoff is at total notch occlusion.

See it at the bottom of this page:

http://www.kellyaerospace.com/articles/Accessory_AMT.pdf

Dan
Click to expand...

Dan I just went through my text book (A&P) on fuel supply. Some things that you glass over the first time hit home when you need the information. As long as I have the NA-3SA1 from the C-85 I think I will overhaul it and do all the modifications. I will put the Delrin needle in and add weight to the float. I will have to keep my eyes open for a bottom bowl for the A65. I do not want to get too far just incase I switch both planes over to the C-85.

Dan
 
Tom-D said:
Find an old marvel (salvage yard) and send it to me, I'll repair as required and it will work just fine on your 65 & 85. last one I did was under 200 bucks like new.

I have no problems repairing them.
Click to expand...
Are you still doing this Tom? I know the thread is a bit dated. The Marvel on my c85 stroker suddenly started dumping fuel in at full throttle. Come to find out it is an 0-200 carb (4894 I think) with some STC jets in it for auto fuel. So not the correct carb to begin with, and now it is doing something funky. My thought is to put the correct one on there. But it did run well since 2012 on this carb and it cruises at 5-6 gal/hr in a 140. So maybe send it to someone to test and repair.
Thanks,
Karl
 
Atypicalguy said:
Are you still doing this Tom? I know the thread is a bit dated. The Marvel on my c85 stroker suddenly started dumping fuel in at full throttle. Come to find out it is an 0-200 carb (4894 I think) with some STC jets in it for auto fuel. So not the correct carb to begin with, and now it is doing something funky. My thought is to put the correct one on there. But it did run well since 2012 on this carb and it cruises at 5-6 gal/hr in a 140. So maybe send it to someone to test and repair.
Thanks,
Karl
Click to expand...
Make sure your primer is in and locked. If it's not it will let the engine suck more fuel. Aside from that, an incorrect float level setting or a leaking float valve will let more fuel into the engine.
 
Dan Thomas said:
Make sure your primer is in and locked. If it's not it will let the engine suck more fuel. Aside from that, an incorrect float level setting or a leaking float valve will let more fuel into the engine.
Click to expand...
Kind of sounds like that, doesn't it? I think there is a two piece venturi inspection AD on these Marvels so I will have them pull it off and look at the float valve and venturi along with checking the primer for leak.
 
Atypicalguy said:
Kind of sounds like that, doesn't it? I think there is a two piece venturi inspection AD on these Marvels so I will have them pull it off and look at the float valve and venturi along with checking the primer for leak.
Click to expand...
Look at the carb's data tag. It might have a "V" stamped on it, indicating compliance with the venturi AD. There's another AD that addresses defective floats: https://rgl.faa.gov/Regulatory_and_...DA28338BF3FCB4C786256A410065BB2D?OpenDocument

A bad float can sink and flood the engine.
 
Dan Thomas said:
Look at the carb's data tag. It might have a "V" stamped on it, indicating compliance with the venturi AD. There's another AD that addresses defective floats: https://rgl.faa.gov/Regulatory_and_...DA28338BF3FCB4C786256A410065BB2D?OpenDocument

A bad float can sink and flood the engine.
Click to expand...
Yeah turns out half the float broke off and the float sank. Back in action again. Thanks for the info about the floats. Not sure if this carb was AD compliant, but it came from G&N I think in 2012 who said they overhauled it, and the AD for the float is 1993, so it should have been compliant.

They put another plastic float in; I guess the brass ones can sink also. I think the tag actually does have a V stamped toward the middle on the bottom edge of the tag; seems like it anyway from the photo I have. But I think it still needs inspection every hundred hours as they switched back to two piece at some point.

All this has me craving a Stromberg! Floats breaking, venturis breaking yada yada on the Marvel. Never hear that about a Stromberg carb on these motors that I can see. Grass is always greener I guess.

Hookers going in, new flap handle, right side window latch and then it's back to 140-ing.

Cheers,
Karl
 
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