Running rich, and rough idle, and popping.

Hi all,

I have a 73 4dr with the 302 V8. My father-in-law brought this car down from Colorado for me last week. The car has been burning through gas at an incredible rate. The exhaust smells like gas and the idle in drive and reverse is very rough. The car was only driven between 7000 and 10000 feet in elevation. Now, I'm at about 3000'. I'm wondering what might be causing the poor gas mileage, and the rough idle.

The car is completely stock.

Also, there is a popping noise in the engine bay and the exhaust when the car is in drive or reverse. Any help would be greatly appreciated.

Thanks,
Jonathan

 

I relubed the points in the distributor and that partially eliminated the popping noise. The idle in drive and revers is still there. idle in park is fine. How do I adjust the idle for drive and reverse on a 302V8 2bbl carb?

Thanks,
Jonathan

 

Don't know what carb you have but it sounds like the idle mixture needs to be set and jets checked. Usually a car tuned for high elevation will be too lean at a lower elevation. Also the distributor timing is often pulled way back.

 

Check to see if the choke plate is not stuck shut or out of adjustment when engine is hot. Then go from there on rejetting etc.

 

uhhh i think you have it bass ackwards... usually don't you open things up for the lower atmosphereic pressure? gonna run fine in the mountains but real rich at lower elevations. kinda like a turbo...hicher pressure in gonna force more gas into the carb at lower elevations. lean it out a bit. try to find out if the car was actually jetted for the mountains.

 

Air is less dense at high elevations, less air per cubic foot. So you need less fuel to stay at around 14:1 A/F ratio. That's why carbs have choke plates. The cooler air is more dense and needs to be trimmed for the fuel setting of the carb. Air doesn't push fuel into a carb. The fuel is drawn in by the air flow from the pistons causing vacuum during intake stroke.

Old Guy has a very good point about the choke plate. It's usually something simple.

 

The choke plate is all the way open. I tried adjusting the idle and the problem continued. How to I adjust the fuel mixture? I can't find the mixture screws.

Thanks.
Jonathan

 

What kind of carb do you have?

 

It's the carb that came stock on the 1973 302 V8. It's a 2bbl.

 

I just found it. It's the Autolite(Motorcraft)2100D carb.

Thanks,
Jonathan

 

Scott, I think maybe you have some misinformation. Less air means you need less fuel, more air means more fuel for correct combustion. A turbo does nothing to force fuel into the engine, just more air and if the fuel is not richened up you will run lean and fry things internally as Mavman did while experimenting with turbo's. The injected cars have computers to bring more fuel as the air mixture is increased. Just don't want you to have any problems along that line either. Lets go with another idea on the problem at hand, possible float problem or trash in the needle and seat. I also think a timing problem may be there too, as stated before.

 

I think you're right about the timing problem. I increased the fuel mixture and it seems to be running a little better. I'll get a timing light after a while and adjust the timing. Thanks for all the help.

Jonathan

 

Well, after adjusting the fuel mixture the car was running better. There was still some popping that I believe can be attributed to the timing.

When I got home from work today the engine stalled out. I could not get the engine idling properly after that. I readjusted the fuel mixture and the idle and can still not seem to get the engine idling properly. As soon as I let off the gas, the idle drops drastically and the engine sputters and finally dies. Any idea what might cause this, and how to fix it?

Thanks for any ideas.
Jonathan

 

You might want to check for vaccum leaks.

 

thanks dave. sometimes i don't explain myself well..i know a turbo forces more air in. it was always my thought that in higher elevations, you need to open up the fuel a little bit because of less air pressure. the vacuum created by the pistons going down is replaced by air coming in through the carb. the fuel is fed by this same atmospheric pressure via that little tube that goes into the float bowl.... forcing gas out of the bowl. (not trying to sound at all like a wise guy) dave am i clear on my uhhhh explanation? this is how the carbureation process was explained to me. a guy i worked with always told me he had his best times on days when the barometer was way up. got the most gas through his jets those days. he said he used bigger jets on hot and humid days when the barometer was kinda low.smaller jets on days where the barometer was high. i am certainly not arguing or meaning anything disrepectful. i thought i had a clear handle on this and (as always) completely respect your experience and advice.