Carburetor Icing - possible 'fix' on KT17 with 'teardrop' air filter?

[Jeff-C175 7,203]

I had a terrible time with icing today.  Humidity over 80% and temps hovering in the high 20s, low 30s.  I couldn't run for more than ten minutes at a time before the engine would stall out.  Then I would wait like five minutes, it would restart no problem.  Lather, rinse, repeat... very frustrating trying to get three driveways and a common road plowed.

 

So, looking for a solution and thinking about some of the suggestions given in another thread recently, I hit on the idea of 'clocking' the teardrop air cleaner 90° clockwise.  I removed the rubber tube that goes from the tin around the flywheel to the air cleaner.  I'll duct tape over the hole in the tin for now.

 

This puts the opening into the air cleaner above the exhaust pipe heat shield.  This makes it very easy for me to use some galvanized sheet metal that I have to form a 'duct' around the exhaust pipe and feed this straight up into the air cleaner.  I'm sure this will solve my issue.  The duct will be easily removable come summer time mowing season and I'll just return the air cleaner to it's 'correct' position.  I also have some VERY heavy aluminum 'foil' that I could hand form that would possibly work as well.  Even some aluminum duct sealing tape might work (I have that in stock too)

 

Here's my question...  Regarding the 'breather tube' that comes off the engine and into the air cleaner.  (not the big rubber tube from the flywheel shroud tin, the skinny one coming off the 'valve cover')  How important is that?  I can duct tape over the small hole in the air cleaner to close that off, but what happens if I leave that breather tube not connected to the air cleaner?   I believe that tube is only to route the crankcase blowby back into the intake.  It doesn't spew any oil, but maybe some fumes.  I'm quite sure that I don't want to plug it as this may cause slight pressure build up in the crankcase, not a good thing.  

 

I'm thinking that I can safely just leave it hanging out to atmosphere for the winter.  Does that sound OK?

 

 

Edited February 19, 2021 by Jeff-C175

[Bill D 2,056]

Put an add in the wanted section for an air cleaner assembly and exhaust manifold cover from a  KT 17 out of a 417 A/8  It has the necessary tube to prevent icing.   

 

[Pullstart 63,635]

If you ask Red Green, any idea with duct tape is a good idea!

[953 nut 56,838]

8 hours ago, Jeff-C175 said:

I can duct tape over the small hole in the air cleaner to close that off, but what happens if I leave that breather tube not connected to the air cleaner?   I believe that tube is only to route the crankcase blowby back into the intake.  It doesn't spew any oil, but maybe some fumes.

You may want to attach some filtering material like polyester batting over the end of the tube to capture the fumes. Also I would remove the foam  pre-filter from the air filter for the winter.

[DennisThornton 4,770]

I want to make sure I'm understanding the problem and wonder if "carburetor icing" is the problem or snow clogging up?  I had a 70s something Toyota that would stall under the wrong conditions.  Pull the breather and look deep into the carb to find the the evaporating fuel had chilled so to form enough ice to slow down or even stop the engine.

 

We talking about pulling in snow, clogging the filter or prefilter and shutting down?

[Jeff-C175 7,203]

5 hours ago, Bill D said:

add in the wanted section

 

Problem with that is that I need it yesterday!

 

26 minutes ago, DennisThornton said:

wonder if "carburetor icing"

 

Definitely.  No snow is getting into the air cleaner, dry as a bone, and the intake manifold and carburetor had 'frost' on the outside of it.  Didn't look into the carb throat though, but the symptoms are classic icing symptoms.  And if I blow air from my heat gun across the manifold and carb area it clears up very quickly.  After it would stall it would start back up again in a few minutes after the ice/frost inside the carb melted from the heat soak from the warm engine below.

 

Also, for the first half hour or so it was fine, then the problem started.  Later I went in the house and looked at the weather station and saw that during that time the humidity went from about 40% up to 80% PLUS.  Went up like a rocket.  The local weather guy even commented on that and the onset of the problem coincided perfectly.  My understanding is that carb icing occurs with low temps and high humidity.  The 'dew point' is the key factor.  When it's cold and dry, dew won't form and freeze inside the carb.  Cold and humid, higher dew point, condensation occurs and freezes on the cold carb internals.

 

An interesting (to me) side note to this:  I owned an Isuzu Trooper for years and years and years.  (I really miss that vehicle!)  The throttle body had two small hoses through which engine coolant flowed to warm the body.  Those hoses were VERY difficult (actually impossible) to access without removing the throttle body but the other end of the hoses was simple to get to.  When they started leaking coolant I needed a 'quick fix' at the time, so just like we used to do when heater cores started leaking I 'looped them back' so I could keep driving.  A couple months later as winter approached the truck would run like total crap and stall when the weather cooled.  I discovered the problem was icing inside the throttle body.  My wife's car that I recently worked on has the same deal and I'm betting that nearly every car has some form of icing prevention.  Back in the day it was that tube from the air filter down to a shroud around the exhaust manifold which had a thermostatic 'damper' on it.

Edited February 19, 2021 by Jeff-C175

[DennisThornton 4,770]

2 minutes ago, Jeff-C175 said:

 

Problem with that is that I need it yesterday!

 

 

Definitely.  No snow is getting into the air cleaner, dry as a bone, and the intake manifold and carburetor had 'frost' on the outside of it.  Didn't look into the carb throat though, but they symptoms are classic icing symptoms.  And if I blow air from my heat gun across the manifold and carb area it clears up very quickly.  After it would stall it would start back up again in a few minutes after the ice/frost inside the carb melted from the heat soak from the warm engine below.

 

Also, for the first half hour or so it was fine, then the problem started.  Later I went in the house and looked at the weather station and saw that during that time the humidity went from about 40% up to 80% PLUS.  Went up like a rocket.  The local weather guy even commented on that.  My understanding is that carb icing occurs with low temps and high humidity.  The 'dew point' is the key factor.  When it's cold and dry, dew won't form and freeze in the carb.  Cold and humid, higher dew point, condensation occurs and freezes on the cold carb internals.

Yep!  Weather with lots of humidity just waiting for a little drop in temp.  Never seen carb icing in ANY engine other than that Toyota!  And MAN could it ice up!  Well, we both know the answer, heat.  Somehow.  Remember when some vehicles had preheated intakes and/or preheated intakes?

[Jeff-C175 7,203]

26 minutes ago, DennisThornton said:

Remember when some vehicles had preheated intakes and/or preheated intakes?

 

I was editing when you posted... yup!  

 

My '70 Chevelle SS would ice up because I put a 'performance' air filter on it that eliminated that thermostatic 'nozzle' with the the tube to the exhaust.  I had to install the stock air filter in the winter.  And of course the Isuzu I mentioned after I bypassed the throttle body heater.

 

I wonder about the Toyota... if maybe that had been 'modified' to remove the carb heat at some point?  I had a few Toyotas with the 22R engine that never had icing problems but I don't know how (or if) they heated the intake.

 

I just did a little googling on this.  Most people seem to think that those thermostatic air filter thingies are intended to help the engine warm up faster.  While that may be true to some extent, I maintain that the true purpose is to prevent carb (or throttle body) icing problems.  

 

Fact is though that the vast majority of people will never have to deal with icing conditions.  It's only a problem in areas where there could be high humidity during cool/cold weather.  Noo Joisey shaw is one of those areas.

Edited February 19, 2021 by Jeff-C175

[DennisThornton 4,770]

46 minutes ago, Jeff-C175 said:

 

I was editing when you posted... yup!  

 

My '70 Chevelle SS would ice up because I put a 'performance' air filter on it that eliminated that thermostatic 'nozzle' with the the tube to the exhaust.  I had to install the stock air filter in the winter.  And of course the Isuzu I mentioned after I bypassed the throttle body heater.

 

I wonder about the Toyota... if maybe that had been 'modified' to remove the carb heat at some point?  I had a few Toyotas with the 22R engine that never had icing problems but I don't know how (or if) they heated the intake.

 

I just did a little googling on this.  Most people seem to think that those thermostatic air filter thingies are intended to help the engine warm up faster.  While that may be true to some extent, I maintain that the true purpose is to prevent carb (or throttle body) icing problems.  

 

Fact is though that the vast majority of people will never have to deal with icing conditions.  It's only a problem in areas where there could be high humidity during cool/cold weather.  Noo Joisey shaw is one of those areas.

It took special weather for my Toyota but it was a real pain until the weather changed a bit OR it was driven slower.  I dealt with it until I sold it. 

But I'm sure you can conjure up something since you know what is going on and what it needs.  Some sort of warm air collected and directed.

[WVHillbilly520H 10,376]

Ever try "Heet" in your fuel? Just to see if it would help since its supposed to remove water and prevent fuel from freezing.

[Handy Don 13,129]

I think the issue is moisture in the air freezing in the carburetor throat. It lessens the airflow and blocks the fuel from being drawn in and vaporized.

[DennisThornton 4,770]

13 minutes ago, Handy Don said:

I think the issue is moisture in the air freezing in the carburetor throat. It lessens the airflow and blocks the fuel from being drawn in and vaporized.

Yes!  It is!  It's not the fuel that is actually freezing nor any water in it but the humidity that is already close to dropping out and the cooling of the fuel evaporating helps it do so.  First time I saw it I was amazed!  The venturi was almost closed!  Car would barely run!  Give it few minutes and drive away!  Until it did it again.  If the temp changed up or down a little bit it was fine!

[Jeff-C175 7,203]

The principle is akin to that used in refrigeration systems.

 

As the fuel evaporates and the pressure drops across the venturi it takes the heat with it.  This chills the carb below the dew point and the condensation that occurs then freezes.

[Handy Don 13,129]

35 minutes ago, Jeff-C175 said:

The principle is akin to that used in refrigeration systems.

 

As the fuel evaporates and the pressure drops across the venturi it takes the heat with it.  This chills the carb below the dew point and the condensation that occurs then freezes.

That Gas Law is so persnickety! 

[JohnD 145]

My 1983 KT-17 has an anti-icing system built in. 

I haven't had any issues so I think you are on the right track. 

 

[DennisThornton 4,770]

50 minutes ago, JohnD said:

My 1983 KT-17 has an anti-icing system built in. 

I haven't had any issues so I think you are on the right track. 

 

Never seen a preheater for a small engine! Pulls heater air off the exhaust?

[JohnD 145]

Yes, it does.  We're getting snow here tonight so I can send a photo in the morning.  The heater cover sits over the exhaust pipe, so it pulls in warm air almost immediately. 

[Jeff-C175 7,203]

2 hours ago, JohnD said:

1983 KT-17

 

That's the air filter I call the "top hat" type.  They didn't offer that with the "tear drop" which is what I have.

 

I'm going to do something very similar with mine.  Been busy with other project that must be completed by Mar. 3rd.  By then I may not need it until next winter, but I'll be ready!

[DennisThornton 4,770]

Funny, almost as soon as I say I've never seen that:

 

[JohnD 145]

1 hour ago, DennisThornton said:

Funny, almost as soon as I say I've never seen that:

 

 

Your air cleaner is rotated 180 degrees from the image on the side. 

[DennisThornton 4,770]

3 minutes ago, JohnD said:

Your air cleaner is rotated 180 degrees from the image on the side. 

Obviously different and I don't see how the one in the pic works or helps, but it ain't mine.  Just a pic I shared.  OP has the issue, not me.

[JohnD 145]

No problem.  Just stating the orientation relative to my photo. 

[Jeff-C175 7,203]

20 minutes ago, JohnD said:

air cleaner is rotated 180 degrees

 

Looks like the "Summer" position to me...  and it's CHROME!  

 

I'm doing very similar with my tear drop air filter.  Going to collect air from around the exhaust pipes.  I'll post some pics when I get to it.

 

My heat shield started to crack at the same location.  Drilled small holes at the ends of the cracks and it's been stable for a few years now.

 

Edited February 22, 2021 by Jeff-C175