Carburetor heat problems...

This is an old thread but if you made it this far, you likely have a problem you are trying to fix. I will point out that if your carb is on a Continental, the carb is bolted to the spider which is supposed to be rubber mounted to the engine. Basically it is the intake tubes that hold the spider in place. the two studs that go through the spider are really just there for safety and the nuts are only to be finger tight with a cotter to hold the nut. A fancy "seal o lock" is on either side of the spider so even where it is bolted loosely, it is only rubber contact. DO NOT tighten this assembly up with a wrench or you will shake the crap out of the carb. Foaming fuel, loosening carb and broken air box will surely follow in time.

DENNY said:

Dave
The loose fuel bowl will cause a rich mixture with carb heat. That is what causes the large RPM drop. Leaning the mixture with carb heat on will allow the engine to return to normal operation. I was on the haul road when my problem was at it worst. I had lots of time on my way back to anchorage to figure it out.
DENNY

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Denny, could you please explain how the loose fuel bowl will cause a rich mixture with carb heat? I'm having a similar problem on my cessna 150.

Read the entire post and it will explain it for a 150/160 hp cub. The carb is always running rich but you only notice it when you pull carb heat unless you have fuel flow and proper EGT/CHT in all 4 cylinders. I am not a Cessna 150 guy so do a new post with the plane/engine/problem and much people that know a LOT more than me should reply.
DENNY

DENNY said:

Read the entire post and it will explain it for a 150/160 hp cub. The carb is always running rich but you only notice it when you pull carb heat unless you have fuel flow and proper EGT/CHT in all 4 cylinders. I am not a Cessna 150 guy so do a new post with the plane/engine/problem and much people that know a LOT more than me should reply.
DENNY

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Denny,

Thanks for the reply. I did read the entire post several times but couldn`t find the rationale behind why a loose fuel bowl would cause a rich mixture. From your answer, I understand that the loose fuel bowl would allow fuel to get sucked through the gasket and into the venturi (correct me if I am wrong). If that is the case, then like you said, the mixture would always be rich, but might only be more noticeable upon carb heat application.

I will definitely post my question on a cessna forum, but since the symptoms of the OP were nearly identical to mine, I felt like this would be a good place to start. I am generally a curious person regarding how mechanical stuff works and I just bought my first airplane (C-150), so I am trying to learn as much as I possibly can, regardless of the type of airplane.

Thanks again for taking the time to respond.

Frank

Yep, you got it. Congratulations on the first airplane, go the the everything else forum and put up a post. Things that will help are Your location/plane type/engine/carb/exhaust type/what is the RPM drop with application of carb heat/if you have EGT/CHT how much EGT rise do you get before you go lean of peak. Different planes have different quirks someone here may have had the same issue with one so always good to ask.
DENNY

DENNY said:

Yep, you got it. Congratulations on the first airplane, go the the everything else forum and put up a post. Things that will help are Your location/plane type/engine/carb/exhaust type/what is the RPM drop with application of carb heat/if you have EGT/CHT how much EGT rise do you get before you go lean of peak. Different planes have different quirks someone here may have had the same issue with one so always good to ask.
DENNY

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Thanks a lot for the tip! Much appreciated.

Frank