Marvel-Schebler rear carburetor

[stevesMaule180]

Any late model Maule flyers had problems with
Horizontal (rear of engine) Carburetor as far as idle/ low throttle circuit??

Twice I've had loss of power on the low band. Pretty hair raising.
Both times it has 'acted up' on our MXT-180. Happens after extended runs being leaned out, when you arrive to land, and reduce power.

Little skipping and puttering, then you realize you have no low end power.
It is either full power, or barely running-probably windmilling.

The second time (this past August) we sent Carb back to Marvel plant in N.C. and they said idle mixture was set way to lean.

Anyone else??

[aero101]

Are you richening the mixture prior to approach for landing? I usually verify full rich on mixture before reaching pattern altitude? Are you running your carb heat, and have you installed the newer style carb heat box control valve which is much more effective and reliable then older style? I've never had any problems with mine, but if carb is too lean, or iced up could certainly cause that problem as you descend and things get even leaner? Mine has more likelyhood of icing in warmer wx too, 55F-60F and humid is the worst? Can also cause backfiring which is very hard on the exhaust sys? I have also seen the same problem you discribe when carb slightly loose at base, at low throttle settings you get a gap and it goes too lean to run, higher throttle settings vacuum pulls it up to gasket, seals and makes power? Although this condition can usually be duplicated on ground?

[stevesMaule180]

Jim,
Very helpful. Should I full-rich and carb-heat on final-touch down?

I have not seen that in POH, but could have missed it.

The (other) problem I referred to was recent AD, requiring an idle-mixture pin to get the sleeve or sleeve seat, corrected.
I obviously don't know all the details.

Cost me an additional 800 bucks on my recent annual.

-best

[Mr. Ed]

The AD you are referring to is on the "milled from billet" carbs. Easy to see if you have one of those. Print up the AD and it has photos.

[aero101]

And if you do have Billet Carb installed, the only fix is a brand new cast unit, I haven't had to price one yet, but I'll bet they're not cheap!!! If they repaired yours in field, that's not in compliance with the AD! Very easy to identify which carb you have as AD refers to SB which has pictures at end of text. No pics on the AD itselfYou also always want to enrichen mixture fully somewhere during descent unless you're landing a very high elevations? Carb Heat should be used whenever you pull power back below Green Band, that's SOP? Some engines have a higher propensity for carb icing then others, but last place you want engine to quit is near the ground. If your problem seems to magically take care of itself after landing and sitting a couple of minutes, it was probably carb ice!! Here's copy of SB18A, go to figure #3, if you have machined from billet carb, you need to replace?
http://msacarbs.com/pdf/SB-18_A%20031511.pdf

[Mountain Doctor]

I'll typically leave the mixture leaned for descent. At low power settings there is no way to harm the motor by doing this. It also keeps it a little warmer a little longer to reduce shock cooling. When down to pattern altitude I richen it slowly. I may not go full rich if it's a high altitude (or density) altitude as max power for a go-around would be acheived at leaner than full rich mixture settings.

If a person forgot to richen it, it will act like you describe at low altitudes.

I believe our planes have the same carb, but it may not matter as the principle is the same. May even apply to injected enginges too.