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Old 03-05-2012, 01:02 PM
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help with fouling plugs on winter cold start ups

Hoping someone might give me a suggestion on what changes I might make to my Holley 750 cfm double pump carburetor, so it doesn't foul the spark plugs when the engine is cold. During the warmer months, it starts great, no troubles.
During the winter months, in order to start the sbc 383ci motor, I have to install new plugs. I have no choke which could be the trouble but I also race the car and not sure i want a choke on the carb.
The engine has a large cam, aluminum heads and all the big race stuff inside.
suggestions ?
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Old 03-05-2012, 03:18 PM
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Quote:
Originally Posted by dar130
Hoping someone might give me a suggestion on what changes I might make to my Holley 750 cfm double pump carburetor, so it doesn't foul the spark plugs when the engine is cold. During the warmer months, it starts great, no troubles.
During the winter months, in order to start the sbc 383ci motor, I have to install new plugs. I have no choke which could be the trouble but I also race the car and not sure i want a choke on the carb.
The engine has a large cam, aluminum heads and all the big race stuff inside.
suggestions ?
To start a carburetor vehicle in the cold without a choke you will usually need to pump the gas 5-6 times then baby it. This is what I need to do on my T-Bucket if I start it in the cold weather
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Old 03-05-2012, 03:25 PM
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no choke ????

i'm with chet too... i had a big cam and no choke and had to do exactly what u and chet did... pulled the cam and put in a smooth idle one and don't have that problem anymore.. fires up and idles fine.. lumpy cams are nice but have problems.. ya i know im no help.... my advise is 600 cfm carb and use the cam for a lamp post... but that ain't gonna happen....
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Old 03-05-2012, 04:11 PM
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You can have your cake and eat it also.Stab the throttle a few times..count to ten so the raw fuel can vaporize..crank and fire the engine and stay with the throttle until it builds some heat in the heads.Let your right foot be the high idle cam..enough rpm as to not allow fuel to fall out of suspension and puddle in the intake.Listen to what shes likes..if she blubbers raise the rpm until she levels out and then back out as needed.
Fwiw..my pig wants 1500 rpm for the first minute or two and then I start moving to idle rpm after that depending on ambient.
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Old 03-06-2012, 11:21 AM
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Quote:
Originally Posted by dar130
Hoping someone might give me a suggestion on what changes I might make to my Holley 750 cfm double pump carburetor, so it doesn't foul the spark plugs when the engine is cold. During the warmer months, it starts great, no troubles.
During the winter months, in order to start the sbc 383ci motor, I have to install new plugs. I have no choke which could be the trouble but I also race the car and not sure i want a choke on the carb.
The engine has a large cam, aluminum heads and all the big race stuff inside.
suggestions ?
Hotter heat range spark plug in the winter to keep the tip clean.

Bogie
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Old 03-06-2012, 11:47 AM
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If the motor has a racey long duration cam then the distributor timing curve probabily needs fixing. A stock out of the box curve will not work.

lots of initial base timing at idle.
if you must operate this car in the winter you will want to retain the choke and fast idle linkage.

The intake manifold needs to warm up to get good idle fuel vapouriztion.
liquid fuel will not burn and will foul the plugs.

A heated intake manifold plenum allows fast(er) cold engine warm up.
And helps avoid carb throttle icing. ( cold temp, high humidity )

A RPM air gap or Vic Jr intake that does not have plenum heat makes thigs difficult when its really cold out.

Do not allow the engine to idle slow, when its cold. ( especially with a cold non heated intake manifold plenum and no choke) 2000++ idle rpm speed until the engine warms up.

A slightly hotter thermostat helps in the winter. Slightly hotter spark plug heat range helps on warm ups nad general city driving.
Carb backfires will kill the power valve in the carb.
A blown carb power valve will foul the plugs.

"Winter Gas" Cold weather blended fuel in the winter really helps.
Summer gas will run crappy in the cold winter.
Adding a small amount of methyl hydrate to summer gas ( gas line antifreeze) will help pesky carb throttle icing, some.
"Winter Gas" already has a healthy dose in it.

No substitute to a heated intake manifold plenum and operating choke.
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Old 03-06-2012, 03:50 PM
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Going by where you live and it's climate it sounds like a simple case of carb icing to me. What happens is, when you start the car the air being pulled into the carb the velocity is very high, it's so high the humidity in the air hits the throttle blades and turns the humidity into ice which sticks to the throttle blades plus plugs up the idle circuit forcing the carb to pull from the main circuits which is too much fuel resulting in flooding which fouls out the plugs. You can either connect up a chimney from the headers to the air cleaner or get a carb spacer heater if they just happen to make one for your application or you can just pour half a can of seafoam in the fuel tank at every fillup. Only problem with the seafoam is that gets expensive at 10 bucks a can. You may could look around and find some cheaper additive that can act in the fuel as a deicer.
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Old 03-06-2012, 07:40 PM
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Quote:
Originally Posted by fatblock
You can have your cake and eat it also.Stab the throttle a few times..count to ten so the raw fuel can vaporize..
Umm, what's going to cause vaporization in a cold motor on a winter morning after you've shot a few raw fuel streams into it?
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Old 03-06-2012, 08:35 PM
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Quote:
Originally Posted by 68NovaSS
Umm, what's going to cause vaporization in a cold motor on a winter morning after you've shot a few raw fuel streams into it?
Getting started on cold damp days is a really big challenge. The choke that you don't have is put there to force a vacuum over the main metering circuit so extra fuel will flow into the engine. That combined with the idle flow is supposed to provide enough evaporated (vaporized) fuel to get the engine running. A liquid changing state to a vapor absorbs heat, this being the principle behind refrigeration/air-conditioning. Under the closed or nearly so throttle blades in the manifold a considerable vacuum forms which drops the fuel below its vapor pressure which also helps it turn from liquid to vapor. So all of this lowers the temperature of the mixture to where the water entrained as humidity with the incoming air condenses on the cold metal surfaces of the carb and intake forming ice. The whole point of the exhaust heat cross over in conventional intakes is to raise the temperature of the surfaces and the entering air is raised above the freezing temperature. It also forces vaporization of the fuel which allows a leaner starting mixture which is alot easier on pistons, rings, and cylinder walls.

Whew need a breath. Cold starting by its nature does not evaporate all the fuel being dumped into the engine, just enough to get it running. The fuel that remains as liquid is deposited onto the parts of and in the combustion chamber as carbon/coke (including valves and spark-plug), pushed with the blow-by around the rings taking the upper cylinder lube with it (resulting in fast wear of the parts in this area), delivered out the exhaust as unburnt hydrocarbons dumped into the air you breath.

Now since you don't have a choke, you're supplying this extra rich mixture with the accelerating pump, probably a power valve that turns on with very little manifold vacuum, and most likely richer main jetting than is really required. The sign of all this that you're currently seeing is carbon fouled spark plugs which can be fixed with a hotter heat range to burn the carbon off, this will probably not be suitable in summer even the poor excuse that passes for summer in the Northwest. It was suggested that you construct a heat riser tube from the headers to the air cleaner. This is a trick the OEMs use to get warm air air going soon after start up. These can be made controllable as the OEMs are so they shut off as the engine warms then pull cold air from outside. Another great OEM trick is to heat the engine oil with the coolant (an old big truck and industrial engine trick) This cuts the engines warm up from 10 to a couple minutes. The OEMs put a "cooler" most similar to that used by an automatic tranny into the return tank of the radiator. There are also commercially made units that tap into the thermostat bypass/heater hoses that are hugely effective toward getting the oil and engine up to operating temp quickly.

All this race stuff people get into of cold intakes, no chokes, open air cleaners, etc is fine on the race track when the engine is turning near red line RPMs and the mixture velocity thorough the carb and into the ports is at half a Mach number or better. But it isn't good for a street engine that can't use velocity and turbulence to chop cold fuel droplets into something that looks like a vapor. It is vapor that burns and makes power. If you can't cruise to work and back at WOT, then you gotta think out some other ways to get the motor happy and powerful.

Bogie
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