1991 25hp johnson -frosting carb

[jale]

I have a 1991 25hp Johnson. The carb is frosting on the outside and inside when running in 5 to 10 degree celcius weather. I have to stop and clean out carb with finger to get it going again. Any ideas ??
Thanks Jale

 

[DHPMARINE]

Re: 1991 25hp johnson -frosting carb

Probably the constant velocity of cold air thru the carb throat.Toyota car engines used to do that.Try varying your engine speed once in awhile.

DHP

 

[R.Johnson]

Re: 1991 25hp johnson -frosting carb

Your looking at refrigeration action, in warm weather you whould see water beading all over the carb.

 

[JB]

Re: 1991 25hp johnson -frosting carb

Actually, it is the change in pressure, velocity and temperature in the carb throat that is causing this problem.

As the air moves throught the venturi of the carb pressure drops and velocity rises. Some of the moisture in the air is condensed and when the pressure goes back up the temperature drops, turning the water vapor into ice.

In warmer or dryer air this wouldn't happen. Are you by chance running the engine without the cowling? The incoming air should be warmed enough by the engine inside the cowling before it gets to the carb to prevent this, but at 5*C it may not. Running at lower speeds may allow more warming of the incoming air.

My solution to your problem is to stay home and read a good book when it is that cold and humid.

 

[samo_ott]

Re: 1991 25hp johnson -frosting carb

Even when it's cold out, I'd rather be on my boat than reading a book! Jale has the right idea! But yeah, have the cowling on... maybe hook up a preheat tube off the exhaust manifold if need be... like they do on auto's...

 

[Harker]

Re: 1991 25hp johnson -frosting carb

Probably be easier to allow the motor and inside the cowling to warm up good before dropping the hammer and buzzing off. I hunt ducks in Michigan up to January sometimes and it works for me. Maybe some insulation under the cowling would help too.

 

[60 grit sandpaper]

Re: 1991 25hp johnson -frosting carb

samo ott---When you build a preheater unit it sounds like you need an ice breaker as well!enjoy