For What Its Worth
through my carb and testing the car. Finally my 66 runs as I always
would. Fairly good street manners and good hard acceleration when you
gas. I found it was a few "little" things.
rebuilt it, the carb didn't look too bad, compared to most. Cleaned it,
started putting it back together. I measured all the linkages as the
instructions outlined. What a mess, some measurements wrong from the
some way out from previous shade tree owner.
I found the
secondary's were kicking in 40% early on the throttle position. No wonder it
wouldn't hold smooth speeds going down the city streets. At about 40 it
would want to lung ahead. At the track it would fall on it's face going to WOT, wide open throttle. Opening the
secondary's early, before there was enough need to cause the
venturi in the secondary's to work right. Only a split second
difference I know, but the effect was enormous.
owner had done a number to get it to what
they thought was WOT on the secondary's. The main problem was the
position. About 10 degrees short. No adjustment, just a cast stop on
Factory quality control isn't what it used to be. A little filling fixed
Then adjusted the secondary's back to spec and it all went to WOT just
pump and linkage also way out. The carb just would not idle
down well, It kept a high idle. The linkage to the accelerator pump was
bottoming out. Just barely bottoming out so it gave enough resistance
that the throttle would not always close the last little bit.
I think the
rod was the only
the idle screws. Just couldn't get them to adjust smooth, 1/8 of a turn
from close to way over the hill on the adjustment. One was a little
from over seating, but not bad. Something just didn't look right so I
ones. When I compared them, what a difference. The difference on the
The new ones were about twice the distance from the tip to
diameter, a shallower or longer taper. Now the idle adjusts the way I
should adjust. Looks like another "where did it come from?" part.
time you ask, "how hard is it to
rebuild a carb" be patient with us old guys if
we take a while to answer. It isn't hard after you done a few hundred
or you follow ALL the instructions
in the rebuild kit and have someone with experience looking over your
shoulder. There are things they can't tell you in the
notes on carb rebuilding
- Rebuilding a carb needs
a good memory. Study the instructions and parts as you take it apart.
- Read the instructions.
Most kits have a blow-up of all the parts and where they went.
- Most carbs were rebuilt
to clean out gunk etc. Make sure all the passages are clear.
- Be careful if using
compressed air. You don't want to blow out a pressed in plug causing a
leak. I often used WD40 or similar to check/clean out passages. The
plastic tube on WD40 works great for this.
- Holley's are fairly
simple. Quadra Jets usually take some experience to get the right kit
to plug the "leaky" areas underneath. Also you usually replace the
plastic floats in a Quadrajet with metal ones.
problems rebuilding carbs.
Carb to engine.
Now this is a
topic that can have us all talking for days. Some things from my
- leaving in carb cleaner
too long. It will etch the screw threads and they will strip when
tightening. (The carb cleaners in the 70s and 80s)
- Re-using plastic
floats. Quadra Jets are notorious for problems with plastic floats.
Plastic floats should not be re-used. Replace with metal floats when
- Not adjusting the
floats correctly. Even though you can adjust them later on a Holley, it
is best to have them adjusted close before adding the fuel.
- Dropping the
bearing-valve out of the carb and you didn't notice where it came from.
Most kits have new ones once you figure out where it went.
- Not noticing that the
jets for the primary and secondary are different size/numbers and
mixing them up.
- Playing MR OVERTORQUE
on the screws. Over torqueing the air cleaner screw can bend/warp the
top of some Carbs.
- Not checking the gasket
from the carb to the intake to make sure it really does seal correctly.
Check it on the carb and then on the intake before installing.
- Do not use your mouth
as a pressure/vacuum tester. There are nasty deposits on a carb.
- You can have
too big of a carb. If the carb size is closer to what the
engine needs, it mixes the fuel better, idles, runs and accelerates the
best. Like any engineered device a carb is a trade off of many
design criteria. When running our short track NASCAR many years
ago we ran a 750 CFM carb. Other guys trying to beat us ran 850,
900 and even 1000 CFM carbs. (not as many rules then as
today) We out ran them all. The "extra" CFM was a
- What are you
going to do with it? Street or track?
Weber-Carter-Edelbrock or quadrajet are good designs. A vacuum
secondary Holley is good to. Lots of choices.
- Track, well
shell out the money. Holley, Dominator etc.
- Track and
street, best possible mileage and best performance, your dreaming right?
CFM. Well a quick rule of thumb is take Cubic inches of
engine. 350 for example. Now divide by a cubic foot to get
Cubic Feet of the engine. 1 cubic foot = 12"x12"x12" or 1728cubic
inches. 350/1728 or .2025 cubic feet. (Now you
know why they used cubic inches, cubic feet don't sound as tough)
Now times by RPM divided by 2. Remember these are 4 cycle
engines, it takes 2 revs to get all the cubic inches. So if
my engine should not go over 5500 RPM. .2025x5500/2 or 557
CFM So a 600-670 CFM should be good. If 7000 RPM 708
CFM or a 750 may be better.
want the best, most efficient carb that gets the best power and has good street
and track manners? What
is it? It is called EFI, electronic fuel injection. There
is a very good reason car companies went to computer controlled fuel
injection. Lets face it guys, carbs are simple and cheap and
don't need much computer knowledge to adjust. We can tinker with
them and still have a lot of cash left over.
VHubbard. June 2009
Updated Oct 2012
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