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Carburetor Ice ?

Discussion in 'The Garage' started by Mastiff, Jan 2, 2004.

  1. Mastiff

    Mastiff 1/2 ton status Premium Member

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    I've been having this problem with my Q-jet running like crap in the cold, especially when it's humid out. What it would do is start up fine, then when I kicked it down from fast idle (or about the time I got to the first stoplight in traffic), it would barely idle and normally die if I didn't hold a decent amount of gas. After it heats up, everything is beautiful.

    I did some net searching and then went out and looked at it this morning (40 degrees, foggy) and sure enough, when it's running like crap, I can see ice down in the carb. There isn't a lot, but I can see it building up around the venturis and the butterflies at the base (looking straight down with a flashlight).

    Has anyone else ever had this? I never had this problem with my Edelbrock carb. This is my first winter with the Q-jet (not counting Arizona winters /forums/images/graemlins/tongue.gif).

    I doubt it, but is there any easy way to solve this? I'm sure I shot myself in the foot with the open element air cleaner. The best solution is probably to put the factory air cleaner back on with the heat riser. I've got Doug Thorely headers that have a little thing welded on where the heat riser plumbing can be attached. I don't know how well it will really work though.

    Any thoughts are appreciated.
     
  2. dyeager535

    dyeager535 1 ton status Premium Member

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    Never experienced icing on my rigs either. Most of them were setup for hot air, but not the shrouding on the manifolds, as typically that has been removed due to manifold changes, etc. /forums/images/graemlins/smile.gif

    Actually its kind of odd that you are seeing icing with an open element. Perhaps in combination to getting rid of the heat riser its a problem, but that runs in the face of conventional wisdom and the experiments I've seen, which show and say that underhood air temp is ALWAYS higher than ambient.

    Of course this is my opinion, but on the later trucks, with the much improved air intake over the earlier trucks (the snorkel hooked up for fresh air) I don't like open elements. Just not uch reason for them unless your engine is efficient enough or large enough to demand more air than it can supply, which seems to be quite a bit.

    If you really want a lot of airflow through the "stock" air cleaner, find another stock air cleaner, cut the "neck" off of it, weld or rivet it to yours on the drivers side, and plumb it exactly like the drivers side. You can run dual THERMAC this way, although the drivers side will still be only underhood air, which should still be warmer (and less) than what you get from the snorkel setup.

    BTW, at least '85-86, the extra tall air cleaner was used on some engines (depends on engine RPO) which is the only one I'd use with a dual snorkel setup, and the one I'd look for even with just a single snorkel.
     
  3. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    It would make since why it doesn't wan't to idle very well if Ice is melting and your getting water mixed in when it's still cold. They wan't to die quite easy when you poor water down the carb, usually when I do this I have the throttle held at 2K RPM to help it stay running.

    FYI: Many of you probably already know but to the guys that dont... When you poor a little water down the carb it helps clean out the black sutie stuff that builds up in an older motor.
     
  4. R72K5

    R72K5 Banned

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    it happens now and then, sounds like your exhaust crossover in your intake is not working, and stock air cleaner setup would be better in that it has hot air tube from exhaust manifold stock which helps warm up thje air when warming up engine, and it sucks air from outside of engine compartment on most of the setups,. through the rad support,

    aftermarket air cleaners arent worth much cept for show purposes,. in the 80s they made them good, taller and vented up through rad support, the only thing better than this would be to get setup off an L69 82-92 camaro or firebird, they are dual snorkel and have vents to rad support, almost a form of forced cold ram air when you are movign down the road
     
  5. NITRO

    NITRO 1/2 ton status

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    have ya juss tried using a gas dryer in your tank. somethin like that heet stuff to help get rid of the water? or juss use a different brand of gas. just some other thoughts.

    NITRO
     
  6. HarryH3

    HarryH3 1 ton status Author

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    Carb icing is a serious problem on piston engine aircraft. They can see cold air at altitude at any time of year. Add in just the right amount of moisture and that moisture starts condensing on the cold metal and the carb starts icing up. NOT exactly the sort of thing that you want to have happen when you're in the sky. /forums/images/graemlins/eek.gif Most planes have manual controls in the cabin to allow the pilot to control carb heat. Automotive applications apply carb heat automatically, since the consequences of an iced up carb (or throttle body) due to a malfunction of the automatic setup are much less fatal on the ground. /forums/images/graemlins/wink.gif

    The problem is aggravated as the incoming air moves from a relatively high pressure area (the atmosphere) to a low pressure area (inside the intake). This causes the air to cool even more, so you can see carb icing even at temps slightly above freezing. I knew several people that had carb icing problems when I lived in Massachusetts, but winters there are cold and WET. Reconnecting the heated air intake to the exhaust manifold would clear the problem right up. When the thermostat in the snorkle detects that the temp is below a certain level, it will divert the incoming air so that it must travel past the hot exhaust manifold before entering the housing. This warms it up enough to prevent carb icing. To prevent a loss of power, the diverter valve is set to let air in through the cold air intake momentarily at high throttle positions. As soon as you let off the pedal, it reverts to bringing in warmed air again, at least until it has warmed up enough to disengage. /forums/images/graemlins/cool.gif
     
  7. dyeager535

    dyeager535 1 ton status Premium Member

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    Now that Harry mentioned it, and I thought about your previous lcoation, I'm wondering what temp thermostat you've got in the rig.

    If you've got anything colder than a 195* in there, it isn't helping the carb icing problem. Engine temp is one of the ways the carb gets heat (conducts through the intake) along with the crossover, so if the engine runs cooler, everything attached to it will too.

    Lastly, along with THERMAC, would functional EFE affect carb icing? I can't remember the exact specifics of how it works, (valves, vacuum, temp switch, etc.) but I know it forces the passenger cylinder bank to route exhaust over to the drivers side under the carb in cold conditions.
     
  8. Thunder

    Thunder 3/4 ton status

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    Just another little note. Carb icing can also cause the throttle to stick open. It can build up in the venturies and keep the throttle plates fron closing. There have been accidents and fatalities in stock car racing attributed to carb icing.
    Carb icing can even happen in the summer. Under the right atmospheric conditions.
    If you are having icing problems it might be a wise thing to get it fixed.
    To fix it:
    Hooking up the stock Thermactor warm air intake system is about all you can do.
    When you put on headers you pretty much disabled the manifold heat riser system. Which depends on the butterfly valve in the stock exhaust manifold to close and force hot exhaust gasses thru the passages in the intake manifold to keep the carb base warm.
    One other thing you can do is get a heated carb base plate.
    They are a carb spacer that routes a heater hose thru it to keep the carb warm. I have had to use those heat plates on Inline 6 cyl engines I have built with 4 bbl carbs, intakes, and headers. Because the carb is so far fron the engine they always iced up.. Carb base heaters work good and should solve your problem.
    I know 454 TBI uses a similar base plate heater because of possible icing problems. But I an not sure if GM used them on carbed 454 engines. If they did, you may find one in a junk yard cheap.
     
  9. Mastiff

    Mastiff 1/2 ton status Premium Member

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    I may have used the wrong term "heat riser". I still have my old air cleaner, but my intake manifold is aftermarket. The headers have a place to attach the ducting up to the factory air cleaner thermac thing, so I'm going to try that and see how well it works.

    There's really no problem if I let the thing fast idle for a few minutes (like 5) before I pull away, but if I just wait for the choke to open and go, that'll be too early and the ice problem may develop.

    I need to sand blast the old rusty factory air cleaner and get it spiffed up before I can test this stuff out.

    How does the thermac work? Does it open the valve any time the air temp inside the air cleaner assembly is below a certain value? Or is it smart enough to not open if it's really really cold too? I don't think you can have icing when it's 0F out. And if it was cold enough, you might never switch to fresh air, which seems bad.
     
  10. HarryH3

    HarryH3 1 ton status Author

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    [ QUOTE ]
    Does it open the valve any time the air temp inside the air cleaner assembly is below a certain value?

    [/ QUOTE ]
    I think so. It would be much more complex to design a dual-stage thermostat and GM is too cheap to do that. /forums/images/graemlins/wink.gif But airflow still isn't a problem. The flapper will still open when needed, as I explained earlier:
    [ QUOTE ]
    To prevent a loss of power, the diverter valve is set to let air in through the cold air intake momentarily at high throttle positions. As soon as you let off the pedal, it reverts to bringing in warmed air again, at least until it has warmed up enough to disengage.

    [/ QUOTE ]
     
  11. dyeager535

    dyeager535 1 ton status Premium Member

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    Yes, the switch is in the thermostat housing, so it's aying attention to air temp right where it's ingested, after it has time to warm up as much as it's going to.
     
  12. lukebaby1

    lukebaby1 1/2 ton status

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    I had this problem once, turns out when I changed the manifold gaskets, I used a high quality Felpro Blueline and left the metal restrictors in the center water jacket crossover. After reading a little I discovered that they should have been removed for stock applications. Lets more coolant pass through thus warming the base plate of the Carb. /forums/images/graemlins/wink.gif
     

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