Engine issue in cold temp

[Hockeystud87]

Went flying today and it was chilly out around 32 degrees at the runway. I did my normal run up and waited till the plane was warm having little issue. My carb sensor was showing just around 10C (50F). My carb sensor has a yellow arch between +/- 10C. Which I think signifies the spread in which there needs to be consideration for icing.

As I took off the engine had more vibration than usual. It didn't sound rougher just little more vibration. We did a few patterns and I noticed quickly that the carb sensor was showing an average of 4C. When pulling carb heat it would move again back towards 10C.

We decided to fly off to the next airport and along the trip it was showing 0C and the engine was beginning to sound rougher. I pull carb heat as I know the signs of carb icing. The engine had a little dip in RPM but my carb temps did not rise much past 3C-5C. The increase in temps was not impressive.

The plane gave a small hiccup and I turned around and headed back. As I was pulling carb heat on and off as we flew it was again not increasing carb temps by a considerable amount. It was dropping RPMS tho. At one point I had carb heat half open, then when I pulled it full open the engine gave a cough.

Can all this be attributed to just flying in too cold of weather?
Was there a upgrade on the carb heat that my old 92 doesn't have?

[rv9ralph]

What engine are you running? Which model Kitfox?

Ralph

[Hockeystud87]

Model 4 Speedster with a 912ul. With the carb heat.

[Slyfox]

out of 14 years with my kitfox between the 912ul and uls engine. I've put about 1600 hrs on the ul and about 500 uls engine. I've flown in the most ekk weather from about 20 degrees all the way up to summer at 104 degrees. have flown in a full blown snow storm (still vfr) you name it. if it was vfr, I flew, never, never have I had ice problems in the carbs. sorry don't buy it. No I do not have carb heat on my airplane. always flew with the little K and N filters.

[Shadowrider]

Not familiar with a Rotax, but carb heat enriches mixture. Any chance you are rich and adding carb heat made it rich stumble?

[Slyfox]

not saying this is your problem. but with all the carb float problems out there, have you weighed your floats. 3 grams a float is a good float. also have you checked to make sure your choke is ok, is it returning after you use it.

[jiott]

My understanding is that you are using the carb heat kit that uses the engine coolant to circulate thru a block that keeps the carbs warm. My question is why were you turning it on, off, and partial? It is intended to be always ON because it doesn't heat up the incoming air or change the mixture/power in any way. I agree with Slyfox, sounds like your problem was something else.

[Hockeystud87]

My understanding is that you are using the carb heat kit that uses the engine coolant to circulate thru a block that keeps the carbs warm. My question is why were you turning it on, off, and partial? It is intended to be always ON because it doesn't heat up the incoming air or change the mixture/power in any way. I agree with Slyfox, sounds like your problem was something else.

I have the carb heat box that is attached to the top of the engine and uses warm air off the exhaust to provide hot air into the carbs similar to a traditional carb heat setup.. This is different and the carb heater kit that is what you have stated. I have heard great things about this and am considering using this.


out of 14 years with my kitfox between the 912ul and uls engine. I've put about 1600 hrs on the ul and about 500 uls engine. I've flown in the most ekk weather from about 20 degrees all the way up to summer at 104 degrees. have flown in a full blown snow storm (still vfr) you name it. if it was vfr, I flew, never, never have I had ice problems in the carbs. sorry don't buy it. No I do not have carb heat on my airplane. always flew with the little K and N filters.

From what I can gather the guys who run in your configuration all report the same results as you. This is mostly due to the fact you are essentially always running carb heat from the warmed air that is located at the fire wall as it has run over the engine. So you are always getting warmed air into your carbs. This can theoretically reduce engine performance as it's warmer air. The design I has provides cool rammed air directly into the carbs from directly in the flow of air under the cowl.


not saying this is your problem. but with all the carb float problems out there, have you weighed your floats. 3 grams a float is a good float. also have you checked to make sure your choke is ok, is it returning after you use it.

I just replaced the floats this year and weighed them before going in and they looked good. I did not replace the viton tipped needles and they were pretty old so that might be on the list to look at. The choke is another thing to consider and will look at it tomorrow when I go to re-torque the prop. I will say tho in warmer weather the plane runs perfectly fine with no issues. I have some slight vibrations that are nothing to do with the engine performance.

I am debating on whether or not I should actually get the carb heater kit that warms the carbs and not the air. This provides again theoretically no power loss as you're not heating the air but just the carbs them selves to prevent water freezing.

It would seem that getting the carb heater kit would only be trying to solve a problem for something that is only a issue for a very small portion of when I fly.

[jrevens]

With the Rotax carburetor manifold that connects both carburetor intakes to a common chamber and allows direct ram air to the carbs, it would seem that carb heat would be definitely recommended as a necessity. The warm engine compartment air source for the set up like Slyfox (& many of us) have, has proven it to be unnecessary according to a whole lot of builders/owners with many, many thousands of hours of operation. That is what I’ve been told anyway.

[Hockeystud87]

I agree that it seems that is true. I think my choice is going to install the carb heater kit for the small 1lb increase in weight and no power loss. This would probably negate the need for the carb heat but allows for double protection in case of a serious scenario.

[jiott]

I have seriously thought about that carb heater kit, just for "feel good", but it bothers me that it adds 3 new hoses and 6 new joints to the cooling system plumbing. Lots of new potential failure points-not sure its worth it.