Carb question, Too big?

I have a 72 Lark with a 350, ta intake, ta headers, and a flowmaster exhaust. I still have the points system, though i did replace the coil with a stronger coil. Everything else short of air filter is stock. Oh, and Im completely new to Carbs and V8s.


Ok, basically the carb on my car is a Holley Reman and its in poor shape, really limiting the performance of the car and the fuel economy (~8mpg on the HWY:eek2: ). I purchased a 800cfm carb after reading on here that a bunch of guys liked them. The carb was completely rebuilt by Bill Salvo and according to the guy I bought it from, it was set to factory standards for a 69 430ci engine, but the fellow I bought it from mentioned that since the carb was not a 69, he opted to get rid of this one.

Question time:

Should this carb be a bolt on and go?
What mods are necessary if any?
What are the two screws (with springs) in the front of the carb for?

7043240 LA 1283 is the number of the carb.

Also, I just noticed that there are two small fractured on the main body, just below the gasket infront of the Quadrajet logo. Is this area vac. sensative? I suppose that if this carb should just bolt on, then I should be able to tell if the fractures are leaking.


Thanks in advance,
Kevin

 

Hi kevin have you had your exhaust done. Kerry is a pretty cool guy. He also is very knowledgeable on tuning. Give him a ring and say phil said to say hello.

 

Kevin you have a there a 1973 carb. It will bolt right up to the TA intake. You should see a big improvement with this carb. Fuel economy for sure. I'm not following you on the cracks in the carb. They may be casting scale but I would need to see a picture. Any crack in the carb body is not a good thing. The two screws in the base plate on the front of the carb are your idle mixture screws. they adjust the idle quality. You should do a search for Q-Jets on here and you will likely find every thing you want to know about a quadra jet.

 

Phil, I took care of that this week. I asked Kerry about that also, but he mentioned he is not really good with Q-jets, he prefers Holleys because he knows them already.

So, Im sort of back on the road, now my alt crapped out. ou: But I guess it works out that way sometimes.

 

Hey Kevin,

My 72 had the T/A intake, a 3/4" carb spacer, and an 800cfm Q-Jet. I know a lot of guys seem to like Holley carbs, but I went thru several before I finally pulled a Q-Jet from an early 70's pickup and rebuilt it. What you need to do is pick up a copy of Rochester Carburetors (BK-HP14) by Doug Roe and read it like the bible.

Doug Roe was one hell of an author and hot rodder. I spoke with his wife back in the mid-90's when I called him to thank him for writing one of the most informative books I've ever read. She told me he'd passed away but thanked me for calling, because every now and then someone would call out of the blue to say the same thing.

On to the Q-Jet...

There are almost a hundred diffferent rear metering rods and there's atleast 15 different hangers. The book helps you identify the rods and the hangers by their markings and you can adjust the secondarys to get the perfect combination to suit your needs.

The Q-Jet gets a bad rap because no one seems to understand them. Read this book and you'll discover how rediculously simple they are to rebuild, tune, and maintain.

My Buick will start every time with 3 pumps of the pedal and a turn of the key. It's got a Poston 116 cam (discontinued), Competition Cams rockers and shafts, 10.25:1 compression with .030 pistons and '75 rods, accell supercoil, MSD 6AL ignition, Hooker SC headers back to SuperTrapp racing suppressors (they're only loud when you tromp on it ). The carb is fed by a Holley blue pump in the trunk regulated to 7psi at the firewall.

You're on the way to a great combination.

 

Phil have you raced your car in this configuration and what are your best times as well as your average times?

 

http://www.amazon.com/exec/obidos/t...f=sr_1_1/104-6042589-5895947?v=glance&s=books


Rochester Carburetors
by Doug Roe
$12.57

 

She'll run consistant 12.50's all day with a best of 12.37. I get some scoffing sometimes but that's running her with the timing kicked up a little and on 109 octane. (I wonder what the price is on that nowadays).

The rear axle is a 3.70 and I built the lower control arms from 3"x1.5" rectangular steel tubing and polygraphite bushings. They're 1/2" longer than stock center to center. The upper control arms are boxed and have 1/8" washers welded to them on the outside as reinforcement. The rear springs are from a late 70's Grand Prix, and the fronts are heavy duty springs I gut a full coil from to get the ride height I wanted. The front control arm upper shafts are offset ones I got from Moog back in the 80's.

I actually think it's all the suspension work that get's it down the track. She rides like an old pickup-truck but she takes corners like a slot car.

 

Thats a fast 350:grin: Now how does it run on the street? Is the cam to big for street use and how much stall do you have?

 

The cam is a .480int/.495exh. The exhaust is 2-1/2" all the way to the suppressors in the back.

It's got a 3000 stall, which helps with the idle. It's kinda lopey but I get good vacuum and the ignition is hot. I run AC plugs one size colder, so if it's in traffic for a long time the plugs want to foul up. If she runs on anything but premium I have to retard the timing to get rid of the ping.

I used to average 14mpg on the highway.

The motor was built by a friend of a friend. He used to build marine big-blocks for use on Lake Michigan.

And that 12.50 should actually be a 12.90 :grin:

 

Thanks everyone for all of the help!
p It looks like im a bit late for tonight, but Ill try to install her tomorrow and check things out and Ill report back here any news. Thanks again!

Kevin

 

Headers

Kevin, how did the headers work out for you?

 

Paul, the headers worked out great. Thanks. The installation I hear was a bit rough (exhaust shop guy did it since I couldnt lift the car high enough) however there is still one bolt missing so there is a tick. It seems the fellow's hands were a bit big for the job, so im going to incorperate the help of a friend with little hands when I see him.
But otherwise, im very happy. (sounds a little like a mustang though with the flowmaster system on it.... but not too much)
:eek2:
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Carb question again. How does the butterfly (throttle plates on the top air horn of the carb) open (the secondaries)? I cant seem to figure it out? (ok, I know its supposed to be via vacuum but Im not seeing it).

And another question. There is a large hammer that allows the secondaries to open up( on the base plate), if the hammer is down, the plates open. If the hammer is up, the plates stay closed. How does the hammer move? (Also vacuum I assume but cant figure it out either). Thanks.

Just trying to make sure the carb is fine before i install her!!!

Thanks in advance,
Kevin :TU:

 

ANOTHER QUESTION!!!


Ok, Im feeling kind of dumb. But here it goes. The old carb that I took off of the car I noticed when placed side by side was missing a vacuum nipple. The smaller nipple on the main body of the carb on the drivers side about half way from the middle and bottom on the main housing!

Ok, the problems with this carb, the gas mileage sucked. When I pulled the carb off, there was a pile of gook near the two pockets on the front of the carb, plus the lever that looks like an oil head... on the driver side front of the carb, that pushes a thick rod down the throttle cable is pulled... this thing leaks gas out of the top of the rod.

hmmm... what to do?

 

Kevin,

The secondaries are for all purposes mechanical in nature, It's the metering rods and the upper throttle-valve (butterflys) that are vacuum actuated.

The butterfly valve on the top is tipped in by manifold vacuum when the secondaries open. The rate of tip-in is regulated by the small vacuum pot on the right side (passenger side) of the carb and by a very small tension spring that's got a slot head to adjust and an allen-head screw as a set screw. The spring can be adjusted soft or stiff and tuning this action can remove the "throttle bog" that usually comes on when the secondary throttle valve tips in and the metering rods allow the gas to flow.

Although I don't recommend it, you can totally remove the vacuum brake that regulates the tip-in. I pulled mine but it took a lot of trial and error to get the spring tension "just right".

The thick rod you mentioned is actuated by a lever that comes off the linkage on the drivers side of the carb. This is the accellerator pump. It's likely it may need replacing because it acts in the same manner as a plunger in a tube. If the plunger is cracked from age, gas flows past the cracks and sit in the top of the bore above the plunger. When the plunger returns up, the gas gets squirted out of the top of the carb from around the shaft.

The two pockets underneath are where the primary metering wells are. They're notorious for leaking but if you clean the carb real well and get all that "gook" out, you can get some real good, solvent resistant epoxy and pour it into these little areas. Let the epoxy cure to full strength and you'll get rid of any leakage, and your car will start better after sitting because the fuel in the primary bowl won't be leaking past into the manifold anymore.

As for that vacuum nipple.. You were probably leaking vacuum and it makes it hard to set the idle mixture. As for gas milage, with all these things coming into play it's just time to do a good rebuild on that carb, and make sure all the vacuum hoses are connected. :laugh:

-Phil

 

Phil,

Thanks for the heads up, Unfortunately shortly after installing the 800cfm carb, Ive taken ill. The fever is gone now, but the coughing is pretty annoying.... limiting me from my school work and the car. Anyway after i had installed the 800 on the car the throttle responce was immediate and very nice until... I think the secondaried opened. part throttle or full throttle off idle is very nice and crisp. part throttle in second (80%) is better than 100% throttle in second... Im guessing because the rods are incorrectly sized? Unfortunately Ive only had the oppertunity to think about this from by bed...not from actually doing anything.

Kevin

 

I would try some more juice in the ign.

If you just watch your points you can run dual coils.
[ two stockers are fine]
Make your own wire with two. Stripe off some insulation without cutting the wire and use a good metal crimp.

Made a hell of a difference on a 68 Galaxie I had with points.

-Matt

 

What you're experiencing is probably a lean bog caused by the secondary air butterflies tipping in too quick.

When you give 80% throttle, the secondary metering rods are still partially in the wells. At full throttle, the rods get exposed to where just the ends are sitting in the wells. This would cause the car to run rich, but it shouldn't be enough to bog it down unless you had very narrow rods or rods that had an aggressive taper.

I think you need to increase the tension on the spring for the secondary air valve (the butterflies on top that lift the rods out of the wells) so that they tip in a little slower. Make sure you're careful because you should only be turning that sping about an eighth of a turn (1/8) at a time. You shouldn't go more than one full turn in any case.

If you're at full throttle and the bog hits, but then the car picks up momentum and you feel power come on, then it's the air valve. If you bog out at full throttle and power never comes back on until you let off the throttle, your secondary rods are probably too rich.

To tell what's what as you make these adjustments, you should look at your plugs. Pull one out from each side and see if they're clean or carboned. If they're black, they're rich, if they're white, they may be too lean. If you have just a tinge of brown on them you're just right.

Another thing you may be experiencing is that you're over-carbeurated. You can actually adjust the cfm of the Q-Jet by restricting the amount the secnodaries open. It's explained in the Rochester Carb book I mentioned earlier.

-Phil

 

Phil,

Thanks for the tip. I checked the plugs, and they are lean. so it seems there is more work to do on the carb.
I guess I should start with the spring? Funny thing, is I was looking at my old GSXTRAs and found something sort of on the same line.

Thanks, kevin