I have a 1977 volvo with b21a engine. When the car is cold it runs uneven and misfires for a few minutes, until it reaches correct running temperature.

Using the choke decreases the misfires, but only if I turn it up so that the engine runs at around 3000 rpm.

Also, while it is cold, it produces a LOT of white smoke, like ridiculously much. This disappears when the engine is hot again. It does not consume neither coolant or oil, so I can't understand where the smoke comes from.

What could be the problems behind this? Are the problems related somehow?

 

Is it SMOKE or STEAM? This time of year it's cold and condensation is more visible. Also, the fact that you are at 3,000rpm means lots of exhaust. Since you are not losing either coolant or oil, you are OK!

As far as the misfire, how's the "tune up", plugs, wires, cap, timing, etc? Do you have a cold start injector on that car? The coolant temp. sensor may also be faulty not sending the signal for extra fuel at start up... Did this misfire start all of a sudden or has it been like that for a while, or gotten progressively worse?

 

More like steam. It also smells a bit like gasoline.

The b21a has a carburettor with manual choke for cold starts. I have tried to pull out the ignition cable to each of the spark plugs to see if I could isolate the problems with misfires, but to no avail. Could it be the ignition coil going bad? The distributor seems fine, changed the cap and arm in it a year ago, and it didn't have any wobble or the like.
If it was the ignition the problem should be constant, not just when cold, right?

 

Well, no, ignition problems can be worse when cold, wet, etc. What's the condition of the plugs, wires? What kind of plugs are in there? Make sure you are "tuned' up before all else! Sounds like that type of a problem. You can also very possibly have a carburetor/choke problem that clears up once the car is warm. What kind of carburetor do you have, stock? Is this a US version car?

 

cold engines *need* a richer mixture to run smoothly, with a carburetor, that's the function of the choke. fuel injected cars have a engine coolant temperature sensor and simply inject more gas automatically when its cold.

 

The carburettor is a stock SU HIF6 if I am not mistaken. I have checked the resistance over the ignition cables to see if they are worn, but it seemed like they were up to specs, also they are quite new.

 

Is this a world market car? I thought *all* US model 240's, even 1975, were F series fuel injected engines?

 

No, it is a Swedish market car. I have asked about this issue on Swedish forums, but no-one seemed to be able to come up with an answer to this!

 

Carbs are becoming a bit of a lost art, few mechanics want to touch them. But, well, if it's not a "tune up" issue, then it's the carb... Sorry to be so vague.