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Old 12-21-2002, 07:02   #1 (permalink)
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Why is my car so fast when cold??

My XF carby model absolutely hammers in the first few minutes of driving when it has been sitting for a couple of hours. This happens regardless of the temperature.
Why does it happen???
My theory is that the choke is open allowing more fuel to enter the engine hence more power? Can i make the carb do this all of the time??
If im wrong what else could it be??

Thanks guys
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Old 12-21-2002, 11:33   #2 (permalink)
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When the choke is open, that's the normal operation. A closed choke "chokes" the air from the engine, rich mixture=easier starting, so your choke would be closed, not open at start-up.

Quote:
This happens regardless of the temperature
Air temperature or engine temperature?

You could look it from another angle, is the car running normal when cold and craps out when it gets hot?
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Old 12-21-2002, 15:43   #3 (permalink)
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colder air is more dense therefore you get more fuel/air in that when it's hot.
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Old 12-21-2002, 15:58   #4 (permalink)
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So its not the choke making my car faster then.

Sorry i should of mentioned it occurs when the engine is cold.
I dont think its the colder air making it faster either because the car does it all the time in both hot weather and cold. But only for the first few minutes of driving.
Thanks guys
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Old 12-21-2002, 16:59   #5 (permalink)
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Hi Dan, what XA said is true. The air would be cooled by passing over the cold metal in the carby, intake ETC.
As the engine heats up there will be no more cold metal left, so the air will thin out.
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Old 12-21-2002, 18:50   #6 (permalink)
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But I don't think it would make as much a difference as DansEdgli
is describing.
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Old 12-21-2002, 19:13   #7 (permalink)
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Really it should be slower when cold oil/ combustion is crap on a carb engine till it warms up some as in warm NOT hot though.. I guess its got something to do with tuning of fuel mixture maybe rich which is good for cold start but too rich for a warm motor..?? Maybe the choke it sticking on some or the mixture screw if ther is one adjusted too rich..From memory I think that model or before had a air line going to air cleaner and when hot it would vent air through making it run leaner to compensate for the thinner air, maybe? has been disconected or the small hoses on that carb are not working as should..Too high float bowl can cause this too...Restricted air filter another ???
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Old 12-21-2002, 19:20   #8 (permalink)
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I'd say there is somthing wrong when the engine reaches operating temp, when cold the thing will be reasonably tight so should give worse performance.

With the choke on the a/f mixture won't be anywhere near optimium neither, what the choke does is restrict airflow which is exactly the opposite to what you want to do to increase performance.

I would be thinking along the lines of a sensor failed, possibly a temp one that controls spark advance, it could be reporting an overheat when warmed up which causes spark to be retarded.

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Old 12-21-2002, 21:29   #9 (permalink)
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actually the car will perform and have better numbers when it is cold and has colder denser air. when your intake or carb is heat soaked you are going to be robbing power from your car.

Why do you think that the racers throw ice on their intakes. Why do you think that Nitrous gives such a kick. Besides the gas itself. it actually makes the air/fuel temps colder. Allowing a denser mixture.
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Old 12-21-2002, 21:37   #10 (permalink)
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Mmm Nitrous.

So does this mean there isnt much i can do about it. It just a case of the intake and carby heating up and heating the air before it gets to the engine making my car seem sluggish after a few minutes.
This makes the most sense to me.

Thanks guys.
Dilemma over.

Dan
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