I need some help on a Carb heat problem

[jatkins]

I am up on a lake in semi northern Canada, With my 170b on wheel skis approx 139 nm NE of Toronto.
Minus 13c tonight.
This is a remote area, no telephone, no electrical. The snow is 10+ inches deep at my place.so I had to
Taxi approx 2 nm. To my friends place ( who has satellite Internet ) during the taxi, my oil temp got to
240 as I had winter fronts on. I And I needed to Have 2200 rpm to keep moving. (It took me about 1 1/2 hours to get unstuck from my place. )

Once I got to my friend's place, I let the engine cool for 25 minutes, and removed the oil inlet , winter cover.

I was able to get airborne , ( oil temp was 200 ) there was only 6 inches of snow in his area.
Once airborne, all was well for 25 minutes, then slight ruffness , full throttle only yeilded 2350 rpm ,carb heat on , no change , switched to both tanks, no change.
Checked mags, both ok, I left the carb heat on, and flew 7 minutes back to his place , and landed, on the taxi back all seemed normal , except carb heat gave no change. ( lots of power ) and no change on carb temp gauge.
We we shut down, pulling carb heat on and of resulted in clank, on, clank off, , I got under the plane and I could
See and feel the carb heat diverted plate moving, I can see the arm moving on the outside of the carb box, I can feel the valve moving inside, when runup harb heat results in no noticeable change in RPM , , how ever it appears that the carb temp gauge goes up about 5c in about 2 minutes. I plan to pill the ir filter off in the morning and look inside.

Any suggestions , or recommendations ??

[blueldr]

There seems to be a lot of nice Canacian fellows that spend the winter around Yuma, Arizona. I have no suggestion about your carburetor heat problem, but you might give some thought to Yuma.

[jatkins]

Thanks , I would like to get back home, on Sunday for work.


I am not too certain how happy I would be in Yuma, not too many real forest,
For camping, and good fishing lakes.

I have been to Arizona , many times, in winter, and summer, but I still perfer the seasons.
Not too much ski flying in Arizona?

[FredMa]

check the duct that supplies warm air to the airbox. Could be full of water (frozen) in a low spot of the duct not allowing any warm air regardless of valve position and restricting airflow causing low rpm. could also be something else such as critter nest in the duct. carb "mice", not to be confused with carb ice, have also been known to occur. Not a very pleasant experience for a pilot or the mouse involved. I just thought of the water first since you mentioned the cold temps.

[jatkins]

Good point, Fred, I will check, it first thing this morning, I did not think of that,...... -16c this morning.
It will be a bit of a chore to get it out if that is what it is, but I will be VERY Happy , if I can find that it is
The problem.

Thanks. John

[lowNslow]

I think FredMa has it right. If it is the problem just remove the ducting (very easy, just two hose clamps) and bring it indoors to thaw.

[mit]

Re-evaluate your decision to Taxi that distance in those conditions.

[GAHorn]

If I understand your description well.... it appears you have no effective carb heat.....or you have a blocked/collapsed air filter...or both.

The C.H. butterfly may not be fixed upon it's shaft and may only appear to be operating (diverting cool air overboard and warm air to the carb throat.) Place your finger upon the plate in order to offer resistance, and then see if it operates properly in the open/clsd positions. The butterfly also may not be operating FULLY in each direction, thereby defeating the intent and give NO CHANGE due to warm air when off....and only luke-warm air when ON.

Check your heater-hose and your muffler and muff-shroud for obstructions. (Hint: a blocked heat hose or heater/muffler will behave as you've described....as will a collapsed sceet hose (the kind with an inner-lining which, when it delaminates, collapses when suction is applied....although this is extremely rare and difficult to duplicate.)

Either way...you're on the right track to remove the cowl, open 'er up, and inspect the carb heat system. It's clearly not working correctly with such low results observed by the carb temp gauge.

Do you have a manifold pressure gauge? If so.... what does it display in both ON and OFF positions?

[jatkins]

Hi Tim,
Yes possibility that was not the best choice in hind sight. I thought I could get airborne and stay a couple hundred feet, but she just did not have the power ( O-300 ) . The snow was just too deep.

I am home now and, the problem was the carb heat divirter valve broke in half along the shaft, so when I first
Checked , I could feel the bottom half in place and moving correctly. This is what really baffled me !

The temp the next morning was -16c and once we starter HER, she ran very poorly as the carb still had ice in it and it was so cold over night which made the ice hard. Therefore it took some time to warm the engine and get the carb heat to be effective enough to get the ice cleared out.

[jatkins]

Hi George,
Have you heard of the butterfly valve breaking like mine did ? Along the shaft ?
It looked like the valve was only welded on each outside edge .? Is that correct?

Is that all that holds the valve on to the shaft ??

John

[GAHorn]

That is to what I was referring when I said yours may not be "fixed upon it's shaft". Yes, I've seen several fail in that manner, and yes they are welded to/surrounding the shaft....however if I read your description correctly, your's may have been welded/altered previously in a repair scheme which did not survive.

[bsdunek]

"carb "mice", not to be confused with carb ice, have also been known to occur. Not a very pleasant experience for a pilot or the mouse involved.

I have never heard this one, but I'll sure remember it! Poor little mouse being sucked into the carburetor may be bad for the mouse, but not exactly great for the pilot either.

[hilltop170]

Hi Tim,
The temp the next morning was -16c and once we starter HER, she ran very poorly as the carb still had ice in it and it was so cold over night which made the ice hard. Therefore it took some time to warm the engine and get the carb heat to be effective enough to get the ice cleared out.

How did you get carb ice at -16C?

[jatkins]

My take was,... It got carb ice the day before with temp about -5c , and it never cleared as the carb heat was not working,
Then the next morning it was -16c , and the ice that was allready in the carb, got nice and hard over night at -16c.

I pre-heated, ( oil sump pad and 100 watt light bulb ) then started it once the carb heat was repaired and the engine ran like crap,
until it warmed up and cleared the carb ice. probably -12c at mid day.


John

[GAHorn]

John, ... I'm of the opinion you did NOT have carb ice...but instead had a defective carb heater problem (as you already know of course) ...and that your engine running rough on a cold day was likely frost on a few spark plugs until they warmed up. (Starting a gasoline engine in sub-freezing temps can result in frost on the noses of the plugs/electrodes due to combustion creating water-vapor which instantly freezes upon the frozen spark plug electrodes...which are now shorted out by the moisture. Until that engine warms sufficiently to warm the oil ...which surrounds the intake-inductions passing thru the oil-sump...the fuel is not properly vaporized...and the combination causes rough running.)

It is not ordinarily possible to experience carb ice in sub-freezing clear air because any moisture is already frozen. (However the application of carb heat in such conditions has been found to occasionally re-melt visible moisture (such as ice-fog) and thereby the moisture can enter the cold carb and be frozen into carb ice.)

Moral: Don't use carb heat in sub-freezing clear air or when flying in frozen moisture such as snow, IP, or hail.