what makes cars run bad when cold?

[archemitis]

ok, heres why i ask, i pulled a very high mileage engine out of a spfi wagon, and stuck it into my 86 hatch. im using an ea82 hitachi, with the emissions stuff plugged.

 

on the spfi car, when it was fuel injected, it ran kinda crappy but not real bad, on startup.

now that its carbureted, it runs like crap, for about 5 minutes, almost un drivable.

 

so i was wondering, is this happening simply because my rings and valves arent sealing like they used to, and the carburetor exagerates this? or should i screw with timing some more?

[Setright]

Lack of heat in the cumbustion chamber, mainly. Pistons take a little while to heat up and expand and lose their oval shape. This must affect blowby, and hence the PCV system feeds more gases back into the intake system...cough..cough...cough.

 

The cold will also affect the cumbustion itself, "robbing" heat energy from the explosion and making it less uniform.

 

A carb makes these things more obvious than EFI because the metering is less accurate.

 

I would recommend replacing the PCV valve, to make sure it stays shut a idle. Checking the hoses and then going on to check on the EGR system - if the car has one?

[northguy]

Buy a block heater instead and plug it in.

[Russ Hill]

When an engine is cold, the walls of the intake are below the "dew point" of gasoline. Meaning that, vapoized fuel will condense on the walls of the intake rather than travel into the combustion chamber, causing the car to run lean. The pupose of the choke is to restrict air into the intake so that the mixture will be richened until the intake warms up.

Which usually takes 3-5 minutes.

[archemitis]

oh, that dew point thing is interesting. this old timer put it to me differntly. he said it was everything working misture out of the metal. guess he was kinda right. i think my timing might still be retarded a bit, because even driving, it takes 10 minutes to get up to temp.

 

my pvc is blocked off, and the rocker boxes breath through filters, i have no egr, at all, and no heat tube from the exhaust. that might be something to it too.

 

just wondering in general.

[torxxx]

the pre heater hose is exactly why its running like crap.

Soob carbs like to ice up, thats why they put that hose onto the airbox assembly

 

I bought a piece of marine sea water cooling hose to replace the foil pre heater hose that the car came with.

 

The hose will outlast the car.

 

And let the car idle for 15 to 20 min before driving. Makes a huge difference in the winter time then warming it up til the temp gauge goes above the cold mark.