I'm having a slight cold weather driveability issue. It runs fine when its close to 50 degrees out or warmer. When its down near 40 and close to freezing the engine kinda hesitates a bit under mild acceleration. If I accelerate more and the secondaries open up, the slight hesitation goes away or is skipped all together.
I was thinking that it was the electric choke not opening all the way. It appears that that is not the issue. Is it possible that the air from the fan moving across the choke is causing it to cool down and close slightly while driving?
Does anyone have any idea as to what might be causing this?
If it's running rougher as the temp drops, that's usually an indication of being lean. A cold engine needs a richer mixture. That's what a choke does on a carburetor. Carbs are not as good with the cold weather either as modern efi. That's part of the reason everything is efi now (emissions and MPG are other big reasons for efi).
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1970 Fastback (to be finished outside as a Boss 302 clone)
393 Windsor AFR 205 heads with 11.5:1 compression
Tremec TKO 5 Speed
Link to my Hub Garage and blog about my car http://www.hubgarage.com/mygarage/maxum96
Do you have a manifold stove and heated air tube to the air cleaner or an open element air cleaner? The purpose of the manifold stove and pipe is to gently heat the incoming air so that its density will be stable. As air gets colder it gets denser (condenses) and needs more fuel to maintain the proper a/f ratio. That's what a choke does when the engine is stone cold. The other item that helps cold weather driveability is a manifold heat riser and exhaust crossover, which is a thermostatically controlled flapper in the RH exhaust manifold that, when closed, forces exhaust through the exhaust crossovers in the RH head, through the intake manifold and over to the LH head, then out the exhaust. That's why in cold weather you see cars with dual exhaust only blowing condensation from the LH pipe.
If it's running rougher as the temp drops, that's usually an indication of being lean. A cold engine needs a richer mixture. That's what a choke does on a carburetor. Carbs are not as good with the cold weather either as modern efi. That's part of the reason everything is efi now (emissions and MPG are other big reasons for efi).
I do know what your saying. I'm pretty sure its not leaning out too much in cold weather though. The exhaust still smells rich. The car has always ran a bit on the rich side since we got it back on the road almost 4 years ago. In nice, warm, or hot weather it does run rich. I definitely don't want the exhaust to be stronger than it already is under those conditions.
Isn't the choke supposed to be wide open when its warmed up and running at operating temp? Should it be slightly closed in cold weather when running at operating temp?
Do you have a manifold stove and heated air tube to the air cleaner or an open element air cleaner? The purpose of the manifold stove and pipe is to gently heat the incoming air so that its density will be stable. As air gets colder it gets denser (condenses) and needs more fuel to maintain the proper a/f ratio. That's what a choke does when the engine is stone cold. The other item that helps cold weather driveability is a manifold heat riser and exhaust crossover, which is a thermostatically controlled flapper in the RH exhaust manifold that, when closed, forces exhaust through the exhaust crossovers in the RH head, through the intake manifold and over to the LH head, then out the exhaust. That's why in cold weather you see cars with dual exhaust only blowing condensation from the LH pipe.
It has an open element air cleaner with a Wix filter. I don't have a heat riser.
The carburetor is an Edelbrock 1806 with electric choke. I have not altered the carb's setup from the way it came out of the box. I do have a calibration kit, but have never used it.
Do you have the Air Gap intake or the reg. RPM? I was warned about the Air Gap from my machine shop that they will cause driveability issues or carb icing in the 40s and below but I dont drive in that cold of weather so I got it anyways.
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Kevin
1965 Fastback-Scat 331, Dart heads, FPA headers, Air Gap intake, 650 Ultra DP, Cobra pan, Lunati VooDoo cam 61003, C-4, 10 inch converter, Reverse manual valve body,Detroit Truetracw/3.50s, subframe connectors.
1968 S-code Torino Fastback= project
1966 A-code Mustang coupe=Basket case not sure what to do with it used some parts for the fastback.
Do you have the Air Gap intake or the reg. RPM? I was warned about the Air Gap from my machine shop that they will cause driveability issues or carb icing in the 40s and below but I dont drive in that cold of weather so I got it anyways.
I have the RPM intake. What your saying about the air gap I can see being a potential problem.
I don't really see how the open element air cleaner is the problem. Stock these cars didn't have heat risers either. I know tons of other people with similar setups on everything from Fords to Chevys and so on. None really seem to have this issue when its just chilly outside.
Sounds a little lean to me. Cold weather air is denser. I used to ride motorcycles all year round and I would richen their carbs for very cold weather riding as a mtter of course. The higher strung ones really responded well to this. Though Edelbrocks are commonly known to work nicely "out of the box", they are also known to be a little on the lean side too.
My first move would be to richen the idle mixture a bit. The idle mixture is actually in play for like the first 20% of the throttle into the transition to the main jets so just that might fix the problem. It's just too easy to do and costs nothing.
Beyond that you'd get into total carb tuning. Edelbrock sells a kit for that but it takes some study to get the best out of such work.
If you are reading the plugs, using a tailpipe sniffer, or an O2 tuning kit and know for a fact that it's running too rich at idle and the lower rpm range then I am wrong and it's something else.
FYI, I ran an Edelbrock carb w/ electric choke on my '69 Cougar for many years. It was my daily driver. I also ran an open air cleaner and had NO problem with cold startup or cold driving.
I think it's very likely your choke is too LEAN. Adjust the round, black knob on your choke toward "RICH". Try about 1/8" to start. Keep doing this until the car starts well in cold weather, then smoothly transitions to operating temperature. (And you do have a power source connected to your choke, right?)
The only other issue I can think of is your spark plugs might be dirty from a rich carb. Dirty plugs can fire a cold, rich mixture very well. So, I would recommend pulling a few spark plugs after you've driven the car for awhile after it warms up. If the plugs are anything other than a light gray, it's running too rich. Then buy the Edelbrock calibration kit and lean it out.
FYI, I ran an Edelbrock carb w/ electric choke on my '69 Cougar for many years. It was my daily driver. I also ran an open air cleaner and had NO problem with cold startup or cold driving.
I think it's very likely your choke is too LEAN. Adjust the round, black knob on your choke toward "RICH". Try about 1/8" to start. Keep doing this until the car starts well in cold weather, then smoothly transitions to operating temperature. (And you do have a power source connected to your choke, right?)
The only other issue I can think of is your spark plugs might be dirty from a rich carb. Dirty plugs can fire a cold, rich mixture very well. So, I would recommend pulling a few spark plugs after you've driven the car for awhile after it warms up. If the plugs are anything other than a light gray, it's running too rich. Then buy the Edelbrock calibration kit and lean it out.
The choke is connected to 12v switched power. It does work and takes about 5 minutes to open fully.
I thought about adjusting the choke, but if it is supposed to be fully open at operating temp, how would it be the issue after driving for 30 minutes or even longer?
Sounds a little lean to me. Cold weather air is denser. I used to ride motorcycles all year round and I would richen their carbs for very cold weather riding as a mtter of course. The higher strung ones really responded well to this. Though Edelbrocks are commonly known to work nicely "out of the box", they are also known to be a little on the lean side too.
My first move would be to richen the idle mixture a bit. The idle mixture is actually in play for like the first 20% of the throttle into the transition to the main jets so just that might fix the problem. It's just too easy to do and costs nothing.
Beyond that you'd get into total carb tuning. Edelbrock sells a kit for that but it takes some study to get the best out of such work.
If you are reading the plugs, using a tailpipe sniffer, or an O2 tuning kit and know for a fact that it's running too rich at idle and the lower rpm range then I am wrong and it's something else.
Mine has never been lean that I have seen. No matter the ambient temperature, the exhaust has a fairly strong smell if you stand behind the car.
The choke is connected to 12v switched power. It does work and takes about 5 minutes to open fully.
I thought about adjusting the choke, but if it is supposed to be fully open at operating temp, how would it be the issue after driving for 30 minutes or even longer?
If the choke is open after five minutes in cold weather, it's probably too lean. It's unlikely the engine is actually warm after five minutes of run time.
If you adjust the choke toward "RICH", it will stay closed a little longer. The choke is supposed to close completely when you start the car, then slowly open as the car warms up. Your choke is probably opening up too soon. Keeping it closed a little longer won't hurt anything. If fact, it should make the car run better as it's warming up.
If, by chance, richening up the choke a little makes things worse, just adjust it back to where it was. It's no big deal.
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Cold Weather Driveability Issue
