Carburated cars and weather.

[90ltd]

I had one carbed car before and sometimes it ran smoothly and a lot of times it didnt. I think it was weather related. Do all carbed cars require constant adjustment to compensate for weather? I thinking of buying pre emission (pre 1975) car.

[79lincolnlover]

Extremes in temperature do seem to have a mild effect on starting/running a carbed car. Don't let that stop you from buying what you want though!

[marquisman]

yea, you dont have to be re-jetting the thing when it rains lol. i own 3 carburated cars and the weather has only had little affect on them. they tend to run best on cool and/or damp days. bottom line, i have no complaints. so dont let a carb discourage you.

[mrltd]

if it's tuned right, it'll run great no matter what. I built our bronco and that thing still will fire up in a second in the middle of summer or winter.....my stang didn't have a choke on it and could still fire up fine in the winter....

[90ltd]

yea, you dont have to be re-jetting the thing when it rains lol. i own 3 carburated cars and the weather has only had little affect on them. they tend to run best on cool and/or damp days. bottom line, i have no complaints. so dont let a carb discourage you.

Yeah it ran very smooth when it was below freezing.

[johnunit]

around here (southern ontario, think Minnesota or northern michigan weather) the norm is that if you're running a carb year round you'll have to mess with the tune in the spring and fall, basically a winter tune and summer tune. In general, a smaller carb in relation to the engine will need less adjustment to run reasonably well, though you're giving up potential performance.

Carbed cars also potentially require adjustment when dealing with major altitude changes.

In general though, you won't be messing with the carb any more than you change the oil if you did it right the first time.

[90ltd]

Here in Oregon it rains 8 months a year sometimes for weeks nonstop and air pressure changes rapidly too.

[86VickyLX]

Here in Oregon it rains 8 months a year sometimes for weeks nonstop and air pressure changes rapidly too.

Yes, also, if you're in an area where it changes dramatically quickly (like you live on a mountain etc) You may need to adjust to compensate for pressure changes. This is one reason why fuel injection is superior.

[GoodSamaritan]

Carbs get a bad rap IMHO. Most people judge them based on their experiences with emissions era (70's-80's) carbs. A good pre emissions type carb is a whole different ball game. (I prefer Edelbrock, as it's pretty much a clone of the old carter carbs) Every vehicle I've ever owned that had a pre emissions type carb that wasn't just flat worn out or full of gunk, ran pretty well.

Picking a carb that's right for the engine is the trick. If you are going for all out performance, you obviously want a bigger carb ( higher cfm). You will find though that they don't run all that great for stop and go driving, not to mention reduced mpg. On the other hand. If you plan on driving it regularly, you can get a smaller one. Not only will it run smoother it will drink less gas and have better throttle response at low rpm. I'd go with 530cfm for a 289-351, which should make power up to 5000rpm. A 600cfm will run good on one too, but hurts mpg a bit and really doesn't gain you much.

I run into guys all the time trying to run a 850cfm on a small block chevy 350 and they wonder why it never seems to run right. That would be fine on an all out drag car, but it's too big for a street car.


One last thing. A car with a messed up carb will often run better with the timing advanced or retarded. True story, a buddy of mine had a car with a bad carb on it. (it was beyond rebuilding) When we popped the new carb on, it ran worse. I grabbed my vacuum gauge and set the idle mix, on it and that helped a little but it still wasn't right. When I checked the timing, it was WAY off. I ball parked the timing, and it smoothed right out. Had a lot better power too!

[1987cp]

Carb = good.

SEFI = better (sort of), but not necessarily. A well-planned-out carb'd engine is supposed to be pretty much as powerful and efficient as you can do with typical SEFI options. Elements to shoot for seem to include a large, sensitive modern carb, free-flowing intake and exhaust, big heads, and a small cam designed for a very strong vacuum signal to the carb boosters. Lots of good info at sbftech.com, besides of course some of the practical day-to-day experience of folks here.

Here in south-central Michigan, a functioning choke seems to be all I need to get things going in the winter. And if you can't be bothered to twiddle with timing lights and idle screws ...

[gadget73]

daily driver carbs have a "wider" tune than a race carb. Race carbs are only dead-nuts on for a very specific set of weather and temperature conditions. This obviously does not work for a daily driver application, so they are set up to be considerably more forgiving. With most things, a working choke and high idle cam should be all you need to start it in most any conditions, though you may find you need to let the engine run for a couple minutes before it really runs correctly in cold or damp weather.

personal opinion, but I really dont much like the Carter AFB carbs. I've never had one that I felt made an engine run as good as it should. They are easy to tune because they are fairly untunable. Main jets and metering rods are all you get. That lack of tunability is also why they aren't that great. They came out in the late 1950s, and things did evolve after that point in time. I actually like Rochester Quadrajets, though people think I'm nuts for saying that. Holleys run good when they are right, but I look at a Holley and see a box of black voodoo that I want no parts of. Unfortunately nobody really makes spread bore intakes for a Ford motor, so a Qjet is mostly worthless on one. With a stockish 302 though, a 300 cfm 2bbl will do the job.

[1987cp]

I forgot to mention, on a chokeless carb there's the logical possibility of hooking up an idle dashpot to provide fast idle functionality.

They are easy to tune because they are fairly untunable.

That's probably about right! Makes sense, too - the Aluminum Four Barrel was only Carter's second attempt at making a four-barrel carburetor, succeeding the even earlier Will Carter Four Barrel. This suggests that historically speaking, not even taking production dates starting in 1957 into account, an AFB has got to be pretty crude. And supposedly the aftermarket performances models are even cruder than the ones used in OE applications. Which makes me shake my head in wonder at all the people rushing to put them on expensive engines. Well, except for the fact that they have cost and comparative brainlessness on their side.

At risk of betraying my personal wussiness level, I do rather agree about Holleys being a tad frightening. Gotta drain the fuel whenever making any changes other than float level, and power valves are like $10 each versus $8 for a complete AFB/AVS stepup spring assortment or $35-$60 for a model-specific tuning kit. Holley jet kits seem to easily run $100ish, and that doesn't include power valves, secondary springs, or pump cams. Though, if you look at the Edelbrock #1487 tuning kit, it's obvious why it's so cheap - it contains only three rods and three jets to choose from, which suggests that that's all most people are probably using to tune their 1406s!

[Southern_Pride]

Holleys aren't too horrible to tune. Just takes more time. Mine isn't quite right but its close enough that I don't care.

[1987cp]

Holleys aren't too horrible to tune. Just takes more time. Mine isn't quite right but its close enough that I don't care.

Did you end up getting a jet kit as a starting point, or do you just pick up each part as you need it?

[gadget73]

Holleys seem to be easy to get close. To get them dead-nuts, particularly on a high performance motor, there are so many things to change that it gets intimidating. Air bleeds, pump nozzles, power valves, jets, metering blocks, etc. At least thats how I see them. Maybe because I've never owned anything with a Holley and I've never had to learn to make one go. Most of my experience is AFB, Qjet, and 1bbls. My Beetle had Weber 1bbl carbs, but those things are so delightfully simple to deal with that a brain damaged monkey can make it go. 2 holes on the accel pump lever, one main jet, an idle speed screw and one idle mix screw is all you have. There wasn't even a choke or a high idle system to deal with.