Carb question

[Red69stepside]

Hey guys--

I been off line for a while trying to get settled in a new place. But I'm finally getting back to taking care of my truck and need some carb help.

Only had the truck a few months, and am getting REALLY bad gas mileage, plus I'm smelling fresh gas in the cab a lot, and getting a lot of carbon in my exhaust pipes.

I have a rebuilt 327 and Holley carb. If I'm looking in the right place, the model number is

1850-4
0977

(See pic)

Also the PO removed the choke butterfly from the carb. Would this contribute to low gas mileage?

I heard about carbs with low-flow primaries and big secondaries that only kick in when you need them? Sounds like a good solution if it's real.

Appreciate any help.
__________________

[LUV2XCLR8]

OVER MY HEAD, BUT WELCOME BACK TO HEAVEN

[Brainchild]

IMO that Holley is most of your low mileage.The choke being removed prolly won't make much difference other than cold weather,operation.That is a 600 vacuum secondaries carb right?Hollies aren't noted for great mileage,IMO.

Fresh gas smell in the cab,I'd have a look at the hoses on the lines at the tank,could have a leak.

As far as the small primaries,I think you're talking about a Spreadbore carb,front primaries are smaller than the secondaries.

Like This

[crazy longhorn]

0-1850....thats a pretty good all around carb. judging by the soot, i would guess she has beltched a couple times anyway. a real good "hiccop" through the intake, will blow the powervalve.....then the old chev will run REALLY FAT! Holleys are very nice to tune, (my favorite)& there are many guys on this board that can walk you through it The 1 st thing I would try to tune would be the IGN ......make sure that is "dead nuts" 1st, then go play with the carb. if you talk with this old man on carb.....check the float levels 1st,(you have sight plug s, & external adjustment on that Holley). if that checks ok,set the mix, & idle speed......still fat? after all that, you probably have a blown powervalve. best of luck,crazyL

[Peregrine]

Maybe you just need smaller jets. Before I rejetted mine I could smell gas EVERYWHERE. With vaccum secondaries you can adjust when the secondaries open and get a 6% increase in as MPG. Or so Holley says. If I remember what I read right though if you have very large secondaries your transition isn't as smooth when you accelerate through the point where secondaries open. Plus I'd think they were harder to tune. My 4150 is basically 4 single barrel carbs and came from the factory with the same jets everywhere. Now it has #63 main jets for the primaries and 67 secondaries and I'm still workin it all out.

[Red69stepside]

You guys just blew me right out of the water.

I rebuilt a carb once in about 1976, and still thought I didn't know much about carbs, but I realize I actuallly know NOTHING at all.

Brainchild: "That is a 600 vacuum secondaries carb right?"
I have no idea what a "600 vacuum secondary" is.

Crazy Longhorn: "judging by the soot, i would guess she has beltched a couple times anyway"

"Belched"? I know what that means when I've just chugged a cold one, but what's a carb belching about?

"a real good "hiccop" through the intake, will blow the powervalve"

What's the powervalve, and where is it?

"The 1 st thing I would try to tune would be the IGN"

What's a IGN?

"......make sure that is "dead nuts 1st" "

Hah?

Peregrine:

Are you saying that when you talk about primaries and secndaries, you're talking about the jets?

Anyone know where I can get a crash course in carb basics?

[Brainchild]

Some articles

http://www.truckpulls.com/Tech%20Fil...r%20basics.htm

http://www.chevyhiperformance.com/te...148_0208_carb/

Hope this helps a little.

[Peregrine]

Hehe, I'm still learning to. I learned what I do know from a mid 70s' Holley carb book which is more useful than anything else I've found. I'd try to explain primaries and secondaries, but I'm no good at explaining anything has confusing to understand as carbs. Well, they're aren't that confusing, but it sure helps to have pictures to point to. :P But I'll try to clear it up a little. I was talking about how two barrels open up before the others (the secondaries) They can be the exact same, different jets, different size venturies, or whatever. But the point is that you only need all 4 barrels pouring fuel into the engine at certain times. PM me if you have a particular question, I can open the book and try to figure it out or a way to explain it.

And Brainchilds comment about 600 vacuum secondaries. The 600 refers to the CFM of the carb. Carbs can have mechanical or vacum secondaries. Mechanical secondaries are opperated off of the throtle linkage. Vacuum secondaries have a air bleed that measures the vacuum signal at one of the primaries which opperate a "canister" on the carb which in turn opens the secondaries.

[Red69stepside]

Thanks to all fr the info. but it sure sounds way too complicated to learn before I go broke making the Chevron rich.

I guess the real question is what do I do about this? Do I trash the holley and get a Q-jet, like one mechanic here suggested?

Since the PO said engine was "partially rebuilt" will anyone be abel to tune ANY carb to work right?

I got to do something since I get a bad feeling the whole setup is struggling and not set up right.

[67shortie]

Hate to suggest this (I am a Holley guy to the core) but lots of times guys get used Holleys or problems with thier current carbs and no nothing about making them work leads to more problems than they started out with. Then it's the carbs fault and the bashing begins and the reputation for Holley goes down the drain.

Having said that, it MIGHT be in your best interests to buy another carb, specificaly an Edelbrock 600 with the electric choke. Very trouble free carb, and a good bet that the mileage will see a slight increase on that one too. Most times, you can take that carb out of the box, and bolt it right on and go with minimal setup. A quadrajet is also an awesome carb, but buying a used one or rebuilt is a shot in the dark, Quads are very engine specific and you may get the wrong one for your engine setup/cubes and hate it.

Plus your manifold is most likely a square bore setup and you would need either an adapter for the spread bore or another manifold entirely made for the spread bore carb. The Edelbrock is a universal square bore and it will bolt right on.

No way bashing Holley, but these modular carbs are finicky once and a while and reqire someone who knows what they are doing to really use them to thier full potential. And if they were set up wrong for your application, driveability and mileage will suffer until it its tuned for your engine.

Again, I hated saying that, no insults intended in any way, hope this did not come out wrong, it just might be in your best intersts to replace it.

[68C15]

Originally Posted by 67shortie

it just might be in your best intersts to replace it.

I cannot agree more. I have extensive knowledge on these breeds but trying to explain over the net is very hard.
dont overlook the Demon line-up. they are a "take out of box & bolt on type of deal" if you tell the guys at their tech dept what you have & how you drive.
or, like mentioned before, slap on a Edelbrock 600cfm square bore & go. (there is a reason the street rod guys use them)

[1971LT1SWBPOSI373]

I have a Carter 9635 on my 350 (same as an Edelbrock 1402). It's on a Edelbrock Preformer manifold and it's the Bee's Knee's for a Chevy 350. Lots of performance with good drivability, and it bolted right on. The only hitch is setting it up with a fuel line! TJ
I would also agree, that Holley certainly looks like it needs a power valve before anything else could be checked.