Carb Heat question

[TSUDTELL]

Hi, Still new to me M-5 235. Two questions -
Stall warning light stopped. Does this mean it wont stall?
OK just kidding, I would think it is the bulb. How do you get it out? I don't think from the front and at top of panel would be very hard to get to.

In AK and 20 Degrees today, my first time in it at these temps. Carb heat at 1800 RPM drops maybe 50RPM The carb meter goes from middle yellow to almost out of the yellow.
In the air I just notice the meter move a little. Is this normal? When the temps were in the 40's I really noticed it at run-up. But no ice today on a day others were complaining.
The scat tubing and air valve seem to be fine..

Thanks

Ted

[Mark - AK]

Hi Ted, I am in AK also...at Merrill. I have a carb temp gage and could maybe help but I don't exactly understand your question. I also don't know the function of your gage. Mine reads in degrees. I almost never get carb ice in the winter, but summer -- that is a different story and my carb temp gage has become a very important instrument in the O-540 B4B5 i fly behind. Let me know how I can help.

Mark

[TSUDTELL]

Hi Ted, I am in AK also...at Merrill. I have a carb temp gage and could maybe help but I don't exactly understand your question. I also don't know the function of your gage. Mine reads in degrees. I almost never get carb ice in the winter, but summer -- that is a different story and my carb temp gage has become a very important instrument in the O-540 B4B5 i fly behind. Let me know how I can help.

Mark

HI Mark, I have the 0-540 J1A5D
I never looked that close at the gauge to see what it displays, got to be temp. lets say 0 is center, it is yellow on both sides -10 to +10 (guessing) I just know to keep it out of the yellow if I can.

Let me try this - on run-up in really cold weather I see maybe 50 to 75 rpm drop and engine still feels smooth. In ID where I last flew it, I knew when the carb heat was working, the engine dropped rpm and was a little rough.
I could tell is was working or not with my eyes closed.

Ted

[Mark - AK]

RPM does seem to drop less when it is cold. Hot, (Alaska hot anyway) always gives a pretty good drop. Here is what I do after !6 years in the M-7 235. First, I got a carb temp gage and had my eyes opened at how low the carb temp can go when it is 60 degrees outside. Then I started experimenting with partial carb heat in different conditions and found that, regardless of OAT, if I set carb temp at 42 degrees (plus or minus) I had no further problems with carb ice in the summer, and in both summer and winter my CHT numbers stabilized within 20 degrees or so of each other which means I'm getting better fuel air mixture balance. I cruise at fairly low power because I have floats or skis hanging -- usually around 22" X 2200 RPM. I have gotten no ice now in ten years. There would be no way to do this without the gage. In fact you could easily put the carb into the ice range without the gage. I hope this helps. I am assuming all hardware is working properly. I have grown to love the way this Maule operates. She does speak her own unique language which takes a while to learn. OK -- my flame suite is on and i am ready for anything!

Mark - AK

[TSUDTELL]

RPM does seem to drop less when it is cold. Hot, (Alaska hot anyway) always gives a pretty good drop. Here is what I do after !6 years in the M-7 235. First, I got a carb temp gage and had my eyes opened at how low the carb temp can go when it is 60 degrees outside. Then I started experimenting with partial carb heat in different conditions and found that, regardless of OAT, if I set carb temp at 42 degrees (plus or minus) I had no further problems with carb ice in the summer, and in both summer and winter my CHT numbers stabilized within 20 degrees or so of each other which means I'm getting better fuel air mixture balance. I cruise at fairly low power because I have floats or skis hanging -- usually around 22" X 2200 RPM. I have gotten no ice now in ten years. There would be no way to do this without the gage. In fact you could easily put the carb into the ice range without the gage. I hope this helps. I am assuming all hardware is working properly. I have grown to love the way this Maule operates. She does speak her own unique language which takes a while to learn. OK -- my flame suite is on and i am ready for anything!

Mark - AK

That really helps. Thanks

[Kirk]

Same setup for me, M5-235 O540J1A5D with original carb air temp gauge.

I get a much higher rise than what you are describing when pulling carb heat on. Pretty much close to high end of scale with carb heat full on.

I would say either your indicator is not accurately reflecting what is going on or your carb heat is not coming on fully.

I found the wiring within the cowling on mine to be in pretty poor shape, giving false indications. That wiring takes a lot of abuse with airflow, heat, oil leaking on it and getting bumped or twisted while someone is working in there.

Replacing some of that wiring and taking care to secure it properly got mine working fine.

If your carb heat is not coming on fully, it could be an air box problem or diverter travel problem. My air box needed some rework when I first got my airplane. Checking ducting of course too would be a good idea.

Kirk

[TSUDTELL]

I had a guy look at it, he replaced the scat hose and adjusted the cable but I am getting no where near the heat you guys are describing.
It sounds like a simple system, guess I will tear it down and look at it..

Ted

[maules.com]

Ted, Is the heater shroud firmly attached to muffler, or are the 4 screws missing or is back side cracked as is common. Place a 7" hose clamp around it or a couple wraps of .040 safety wire.
Is the seal attached and sealing on the carb heat door, theres a SB on it ?.
Are the two bolts in place holding door to spindle ?

Stall warning vane is easily bent when cleaning or sweeping snow etc
Is it moving freely up and down.
The switch may click but the circuit is completed by grounding the unit to the wing. Run the two screws in and out which may get better contact.

[TSUDTELL]

Ted, Is the heater shroud firmly attached to muffler, or are the 4 screws missing or is back side cracked as is common. Place a 7" hose clamp around it or a couple wraps of .040 safety wire.
Is the seal attached and sealing on the carb heat door, theres a SB on it ?.
Are the two bolts in place holding door to spindle ?

Stall warning vane is easily bent when cleaning or sweeping snow etc
Is it moving freely up and down.
The switch may click but the circuit is completed by grounding the unit to the wing. Run the two screws in and out which may get better contact.

Thanks Jeremy,
Just saw this..
It's warmer now and seems to be working better. I will check the above, Your right on the stall indicator not grounding...
thanks again..

Ted