Guest georgegrieninger Posted August 11, 2009 Share Posted August 11, 2009 have a 1947 chevrolet that the customer sid was icing up the other morning when it was cool out, this also caused it to starve for fuel? and run bad? He sid when he pulled over to check out the problem their was a bunch of condensation on the bottom bore of the carb, dripping water and cold. I started the fleetmaster six cylinder up today, about 95 in the shade and it ran at idle ok but the carb bore at the base did get cool, but no ice, is this possible in warm, above 70 degree weather and what would cause it? any ideas, cannot find any visible vacuum leaks dwell is 28 degrees. Link to comment Share on other sites More sharing options...
hwellens Posted August 11, 2009 Share Posted August 11, 2009 Sounds like the heat riser is stuck in the open position. Link to comment Share on other sites More sharing options...
Guest georgegrieninger Posted August 11, 2009 Share Posted August 11, 2009 Excellent, I'll remove the manifold an see if i can free it up, Tapping and aerokroil didn't move it, Thanks! Link to comment Share on other sites More sharing options...
carbking Posted August 11, 2009 Share Posted August 11, 2009 A very rich mixture will also cause this issue.Jon. Link to comment Share on other sites More sharing options...
hchris Posted August 11, 2009 Share Posted August 11, 2009 The technical reason for ice to form in the carb is a low pressure area exists in the venturi and moisture ( humidity ) in the air condenses to ice around the throttle plate.The problem with most manifold heat valves is that they dont immediately heat up the area around the throttle plate / venturi area when your engine first fires up, and in fact, you may observe that it could take up to five minutes for that area to warm up on a cool day.My way of dealing with it is to have a piece of heater duct pipe feed hot air off the manifold straight down the air filter inlet ( of course you need a suitable filter housing to do this with ).No doubt those Aircraft Engineers viewing this will recognise that this is common practice for airrcraft piston engines.The downside is that once the engine operates in a warm to hot environment it is not good practice to be feeding hot air into the carb, so it has to be removable or adapted to enable hot air or cool air as desired. Link to comment Share on other sites More sharing options...
hwellens Posted August 11, 2009 Share Posted August 11, 2009 The man said the heat riser was stuck. Seems like if he frees it the icing problem will correct itself without other fixes. Link to comment Share on other sites More sharing options...
hchris Posted August 12, 2009 Share Posted August 12, 2009 As I explained, the heat riser is not very efficient at applying heat to the carb throat / venturi area which is where the ice is forming. So until the manifold is heat saturated there is always the possibility of throttle ice. I have 3 different vehicles with perfectly serviceable heat riser valves and if the atmospheric conditions are right, they all suffer from carb ice until the engine reaches correct operating temperature.However I do agree that a stuck heat riser is not going to help on a cold engine. Link to comment Share on other sites More sharing options...
carbking Posted August 12, 2009 Share Posted August 12, 2009 A carburetor meters and mixes air and fuel. The fuel is then partially changed from a liquid to a gaseous state in the throttle area of the carburetor, and hopefully completely in the intake manifold prior to being induced into the cylinders.Converting from a liquid state to a gaseous state is an endothermic process (it requires heat). The heat necessary for the conversion is called the heat of vaporization. This heat will be removed from whatever surrounds the liquid when the conversion occurs. This may be the metal of the throttle body or throttle plate or the surrounding air.If the heat removed lowers the temperature of the surrounding air suffiiciently, the air can no longer retain the water vapor contained in the air, and the water vapor condenses on the metal surface. If the metal has had sufficient heat removed, then the condensed water will form frost and then ice.As there is a fixed "heat of vaporization" for a given liquid per unit volume; then running an overly rich mixture will cause an excessive amount of heat to be necessary, and contribute to icing. Normally, icing will occur from 35 to 55 degrees F. with higher than normal relative humidity; but an overrich mixture will certainly contribute to the issue."Vee" type engines are less susceptible to icing (although it can certainly occur) than inline engines. Jon. Link to comment Share on other sites More sharing options...
Guest georgegrieninger Posted August 24, 2009 Share Posted August 24, 2009 removed the old heat riser rod and had to install bushings and a new shaft with a new spring. Riser is now functioning. When started wouldnt idle correctly so i removed the caps over the jet ways and blew them out that helped until i went for atest drive and dosent seem to have power fuel starvation? fuel pump puts out three pounds of pressure, well i'll take the carbeurator apart just to make sur the jets are clear. Oh yeah this customer has replaced this carb, A while back but no trouble until recentley. Thanks for the help, sorry for the slow response got a lot of new cars to fix in between. Link to comment Share on other sites More sharing options...
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