Carb heat/electric fuel pump during run up

[Jim Peace]

I always check to see that the carb heat shows me a drop during runup, but after reading the POH for my 1964c I can't seem to find where it says to even check it....

 

So have I been checking this for nothing....

 

What do others do?

 

Also do you guys put the electric fuel pump on for the run up like the POH says?

 

I usually just use it for priming and for takeoff.....

 

After spending almost 1000 for a new one recently I like to use it as little as possible.....

 

 

Jim

 

 

 

[Hank]

I use the fuel pump to prime the system prior to engine start, then check carb heat operation after startup. No carb heat at runup . . .

[Andy95W]

Same as Hank.

[Jim Peace]

Thank you

[carusoam]

It's a safety device, so check it if you have it...

And consider a carb temp gauge if you don't have that...

The little butterfly valve is far from perfect. It probably has a lot of wear, and the control cable likes to stick. Or is that just my C experience...?

Best regards,

-a-

[Oscar Avalle]

I use the electric fuel pump to get fuel pressure up in the green before starting. For a while I did not use the carb heat and then I noticed that the cable got stuck. Now I check it at every run up.

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[orionflt]

I check the carb temp during my runup (last step) then I pull the throttle back to idle to make sure the engine doesn't stutter or try to stall. last thing I want on short final is to have the engine quit because the mixture is not adjusted properly with carb heat on. that would make going around very difficult.

 

Brian

[gsxrpilot]

Fuel pump on just enough to bring pressure up before starting, then on again for the take-off. Carp heat checked for function during run-up. I've only used it a few times to get the mixture to even out a bit in cruise, then back off. Sometimes it can help with LOP operations.  I've never used carb heat on approach or landing. 

[Andy95W]

Carp heat checked for function during run-up.

Carp heat. Because nobody likes a cold fish.

[bonal]

Boost pump for prime and take off carb heat check every run up. weather you ever use it or not its an engine control that should be verified correct before flight.

 

Ok back to work

[DXB]

My M20C transition instructor got me in the habit of also pulling engine back to idle briefly with the carb heat on during runup to make sure it doesn't die.  This seemed reasonable to me and I continue to do it.

 

On a related note, I'm glad I check it in some form- not sure it matters exactly when?  Yesterday, during runup before leaving on a long trip, I seemed to get subtly larger mag drops on both sides.   I then pulled it carb heat and got no RPM drop, and the cable pulled straight out of the panel past the stop without resistance.   The cable had snapped, probably after I used during my last landing, leaving it in the default position without the cable, which is full on.   It broke 2 inches behind the attach point to the carb heat box for no apparent reason at all.  This is a brand new $300 factory cable installed at prebuy in December by an MSC!  Luckily there was enough length on it left for the mechanic on my field to jury rig it in the nearly full off position and get me on my way.  Of course the friction lock mechanism also fell apart, so now I have to hold it in the full on position if I want to use it. I called the MSC mechanic who put it in - he was cool about it and is looking for a new cable to send me - the original spec part doesn't seem easy to come by.

[Hank]

My Owners Manual [see Post #2 above] says to test carb heat function right after engine start, with RPM around 1000; it says nothing about doing it during the runup. Crank engine, set RPM, verify oil pressure, test carb heat, release brakes and start taxi.

 

Worked well for me until one day last winter when my initial climb was very, very slow. A quick peek on the ground after she cooled off showed the carb heat butterfly was fully open, and didn't move when I pulled the handle out or pushed it in. It was made functional again, and life was good, then replaced with new at annual, along with rebuilding the assembly for a tight seal when closed. Now I'm about 10 mph faster . . .

[midlifeflyer]

The problem with older aircraft isn't the aircraft, it's the manuals. Many would say modern POH checklists go way too far but older ones tend to have very little. Pretty decent bet some of the items that were added through the years are because of things that have happened in the interim.

 

WAG but my sense is that the fairly standard carb heat check at runup (as opposed to at engine start or not at all) in later carbureted aircraft is because a long taxi at low power settings in a moist climate could conceivably create carb ice. The carb heat check is to confirm that it is both working and clear of ice.

[Lood]

I was also taught to check carb heat at the run up (on a C172), but NEVER EVER on a dirt or grass surface! I'm not sure how an M20C's carb heat plumbing goes, but on a C172, you suck in unfiltered air when applying carb heat. Doing this on the ground on any unpaved surface is really bad for the engine.

[midlifeflyer]

I was also taught to check carb heat at the run up (on a C172), but NEVER EVER on a dirt or grass surface! I'm not sure how an M20C's carb heat plumbing goes, but on a C172, you suck in unfiltered air when applying carb heat. Doing this on the ground on any unpaved surface is really bad for the engine.

I think that's true for any aircraft with carb heat. Whether or not in the manual, it's always a good idea to minimize the use of carb heat on the ground, even on paved surfaces. Being on loose dirt or grave just makes it worse.

[Hank]

Huh, I can't quote or Copy & Paste . . .

 

But to answer Midlife and FlyingV's concern about developing carb ice during ground ops, that is why leaning strongly on the ground is a good idea. I pull mine back so far that I can't even give enough power to pull from grass parking onto the pavement without choking. It not only prevents carb ice, but also [more important to me] reduces plug fouling.

 

Our engines are fairly resistant to carb ice anyway, since the carb is bolted to the oil sump.

 

YMMV, caveat emptor, and several other Latin disclaimers apply . . .