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Marvel vs. Stromberg carb heat box differences

H

Hekto

Registered User
Herscheid, Germany
Hi,

My flying club operates a 1956 ex-French Army L18C. Equipped with the Conti C-90-8F, it still has it´s Stromberg carb.
It seems here in Europe it gets more and more complicated to have the Stromberg overhauled. Costs are now higher than buying a new Marvel...

With regard to better support, maybe it makes sense to convert to the Marvel-Schebler carb - but what do we have to do?
My biggest concern is the carb heat box. Do I really need a new box? What are he differences between heat boxes for Marvel and Stromberg?

Thanks in advance,
Pascal
 
Not sure about a Piper installation, but I just did a Champ and it required changes to the air box.


Sent from my iPhone using Tapatalk
 
My PA 11 had the original airbox and was converted to a Marvel Carb. I highly recommend a Marvel carb compared to Stromberg. And, install the mixture control....it's a great tool, particularly at altitude, and I used it for hand propping the plane while solo. Prime the engine, mixture to idle cutoff, then prop it from behind, when the engine catches, reach in and push mixture to rich if everything is good. If not, it'll run out of gas pretty quick. A great safety tool, IMHO.

MTV
 
Hi,

Thanks for encouraging me into the Marvel-Schebler direction ;-)
As far as I see, there´s only one Piper-Part no. in the PA-18 IPC. But looking at the Conti IPC, I see carb heat boxes (or maybe "only numbers") for Stromberg, Marvel, and Cessna installations. Little bit confusing...

dgapilot, what mods where necessary on the Champ?

MTV, mixture control would definitely be a nice extra when getting the Marvel.
By the way, our club operates this nice airplane since 1972, never any problems with hand propping - and it´s much beloved by everyone.

Pascal
 
my stromberg works perfect, you can slam the throttle forward as hard as you want and not a iota of hesitation, goes right up to 2650 instantly. i see no reason to get a marvel if your stromberg is in good shape. send it to columbia aircraft, in bloomsburg pa if you think it needs a little attention. price and work is great. and if you get a marvel i will take your stromberg.
 
Both work until cold weather occurs. Then the Marvel can continue to function while the Stromberg may hesitate. It's not if but when in my experience with two Strombergs and many Marvels.

Gary
 
Hekto said:
Hi,


MTV, mixture control would definitely be a nice extra when getting the Marvel.
By the way, our club operates this nice airplane since 1972, never any problems with hand propping - and it´s much beloved by everyone.

Pascal
Click to expand...

I've hand propped a lot of airplanes and it doesn't scare me or even annoy me. That said, for liability purposes, the mixture control just adds another level of safety if used properly.

And, while I've heard folks claim the mixture control doesn't do much for these little engines, I operated mine at Density altitudes of around 10,000 plus and the mixture REALLY helped in those conditions.

To me, it's a no brainer, particularly if you're inclined that direction anyway.

MTV
 
Hekto said:
Hi,

Thanks for encouraging me into the Marvel-Schebler direction ;-)
As far as I see, there´s only one Piper-Part no. in the PA-18 IPC. But looking at the Conti IPC, I see carb heat boxes (or maybe "only numbers") for Stromberg, Marvel, and Cessna installations. Little bit confusing...

dgapilot, what mods where necessary on the Champ?

MTV, mixture control would definitely be a nice extra when getting the Marvel.
By the way, our club operates this nice airplane since 1972, never any problems with hand propping - and it´s much beloved by everyone.

Pascal
Click to expand...

There is an extra piece available fro WA that drops the back end of the air box down so the opening stays centered in the cowl. It also allows room for the bottom of the accelerator pump. With the stock champ air box, the carburetor mounts to a flat plate larger than the bottom of the carburetor, and the protrusion in the bottom of the float bowl in the MS carb won’t fit. The part gets riveted on the air box.


Sent from my iPhone using Tapatalk
 
tempdoug said:
my stromberg works perfect, you can slam the throttle forward as hard as you want and not a iota of hesitation, goes right up to 2650 instantly. i see no reason to get a marvel if your stromberg is in good shape. send it to columbia aircraft, in bloomsburg pa if you think it needs a little attention. price and work is great. and if you get a marvel i will take your stromberg.
Click to expand...

Yup, mine too. And in my experience the Stromberg will static about 50 rpm more

Glenn
 
dgapilot said:
Not sure about a Piper installation, but I just did a Champ and it required changes to the air box.


Sent from my iPhone using Tapatalk
Click to expand...

The Champ uses a unique air box that has the top mounted flush to the carb as opposed to having a short riser welded to the top of the air box like most other planes. So the Champ does require a mod to the air box when you change to a different carb. The Cub has the short riser and flange welded to the top of the air box, so no changes are required.
 
My 90-8F has a Stromberg and a mixture control, but no idle cut off - perhaps unique? Keeps the spark plugs dry:)


Sent from my iPhone using SuperCub.Org
 
Same set-up on my PA-11. The Stromberg mixture control does not have an idle cutoff feature.
 
L18C-95 said:
My 90-8F has a Stromberg and a mixture control, but no idle cut off - perhaps unique? Keeps the spark plugs dry:)
Click to expand...

Waldo M said:
Same set-up on my PA-11. The Stromberg mixture control does not have an idle cutoff feature.
Click to expand...
The Stromberg mixture control is called a "back suction" control. It varies the size of the fuel bowl air vent which in turn varies the float level in the bowl by restricting the amount of "breathing" available for the space above the fuel which varies the amount of fuel which flows out of the main discharge nozzle. This control is optional on the small strombergs. Some have the control wired in the full open position or it could be wired in another position if you are operating from higher altitudes. Alternatively it can be removed altogether and replaced with a cover plate. OR you can hook it up to a control in the cockpit. NO IDLE CUT OFF as the fuel can flow in whichever position is used.

The marvel carburetors mixture control varies the fuel outlet size​ from the bowl which restricts the fuel flow. This control can fully close the outlet from the fuel bowl which becomes the "idle cut off" feature.
 
Hi,

Thanks so much to everyone for all your explanations!
Good to see the swap to Marvel is not so much of an problem. We operate under EASA certification and therefore need an EASA approved workshop for carb overhaul. That´s what makes the Stromberg a bit of a future problem.
Good thing is I have one EASA overhaul shop for the Stromberg and additionally we have the option of changing over to Marvel.

Thanks and best regards,
Pascal
 
I have a 90 horse Supercub and gave up on the Stromberg years ago. Marvel bolts up to the stock Piper/ Univair box with no modifications needed at all.
 
Skipster, mvivion, and BC12D I'd like to hear why you prefer the Marvel Schebler carb over the Stromberg on the C90. I know one of your reasons already.

I have had the same experience that BC12D talked about when the OAT drops toward 20F. I can keep it running on the landing approach and the landing roll, but only with effort and anticipating when the engine is about to stumble and quit. I can see that the engine will quit in that situation if you're not paying attention. I checked it over and the carburetor is set exactly to manufacturer spec. I am running 100LL aviation gasoline. So if the Marvel is not inclined to the same problem, that alone is a pretty good reason to use it.

When Don Swords built up a C90-8 for me, he installed a new Stromberg carb. I had a Marvel on the A65 that engine replaced, but that model M-S carb couldn't be re-jetted or approved on the C90.
 
The MS is probably the best carb out there because it's easier to set up correctly. Accelerated pump aids in cold starts and a smoother throttle response. Most never touch it after its adjusted for your setup. Stromberg doesn't have an accelerater pump but when set up correctly it runs just fine and mine and others have a smooth transition when throttle is slammed forward. Mine has run just fine down to -16F which is the coldest I've flown in so far. I run both, my yellow cub has a MS and my J4 a Stromberg.

Glenn
 
Waldo M what you described is why. Maybe a Stromberg is more sensitive and needs a specific rich idle mixture as temps drop (?). Unfortunately testing for an idle cut rpm rise with a Stromberg might take a few minutes after the fuel is shutoff and the reserve in the lines downstream of the valve gets depleted. But that might be worth a try to confirm the idle mixture. It's easy on a Marvel to see if it's going to climb at lean out. If the Stromberg needs a cold idle setting write it down for later (like 1/2 turn out per so many cold degrees below freezing, etc.)

I ran a Stromberg in 1974 on an 85 Taylorcraft down to -30F but was cautioned beforehand and was prepared for rude behavior. Carb heat and rpm kept it alive in skis. But once on the ground any quick throttle and there were problems. Later on a PA-11-90 I had the same issues as the former owner. He was famous for hand propping a dead engine between touch and goes. The tower was aware and gave him time to relight the fires. Another local had the same problem but in the end the Marvel Hero changeout saved the day (no comics involved).

Gary
 
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