hectre13

iTrader: (4)

ok, so the problems I am having is that my carb idles way too high in park/neutral and way too low in gear, it Idles at about 1400rpms in idle, and around 550-600rpms in gear, to the point that it chugs hard when stopped..

the carb is a vacuum advance, vacuum secondaries aluminum Holley 670 Street avanger, electric choke, i stepped up the power valve to the next size up, and changed the squirter and squirter cam to the next size up.. i can get specifics to this if needed..

my float levels were really low, couldnt even see them in the sights.. they are adjusted now so that if you shake the car you can see them splash up..

on the top of the carb under the choke flap, i dunno if i have the name of the part right.. i think they might be the venturis? at idle one of them leaks sometimes.. which im thinking might be a cause of high idle?

here is the weird thing.. when i first start the car.. if i put it in gear before it warms up.. it idles down to about 1000 rpms.. in the range that i would like it to be.. but after it warms up and the choke opens it drops down to 550 rpms..

anyone have any ideas?

skinny z

Does this problem occur without the vacuum advance connected?
Are you sourcing manifold or ported vacuum?.

hectre13

iTrader: (4)

im guess its ported vacuum because its not on the base of the carb.. i havent tried it with the vacuum disconnected.. i know i plug the carbs vacuum port.. do i need to plug the distributors port also?

skinny z

Unless your Avenger is different from mine, there should be three small ports in the base of the carb at the front. Two are manifold vacuum, the third is ported. I have notes somewhere that tell which is which. You can test with the engine running. (there is another larger port at the back of the carb which is used for PCV.)
It's not necessary to plug the distributor, just the carb.

hectre13

iTrader: (4)

my street avenger has 2 ports on the front, a large and a small, that are on the base of the carb.. the large is for the pcv valve.. then there is another port on the side of the carb with the choke.. and thats it..

if i adjusted my idle to 850 in park.. my car would most deff die in gear.

antsZRS

While this ia up in the air. I have the same carb oh my car. Can someone plz tell me how to adjust the float levels. Mines are way to full when I circled them yesterday. Thanx guys!

skinny z

Potentially you could have several problems.
Yes, the Street Avenger ports are as you describe. (Had to get mine off the shelf to check it out). Typically the vacuum advance is connected to the port on the metering block. That gives ported vacuum for the advance. Some prefer manifold vacuum for the advance however traditionally its connected to ported.
If you have access to a vacuum gauge, it's handy for setting the idle speed and mixture. A wide band O2 sensor is also very useful.
Check the position of the throttle blades at idle to be sure that the transfer slots are not completely exposed (you'll have to remove the carb to verify). The fuel you have leaking from the venturi at idle could be from the mains being pulled in slightly because of an improperly adjusted idle speed screw.
Rather than go through the procedure for setting up the idle mixture (which you may or may not know) check out the Holley web site for detailed info. (Same goes to ANTZZRS for setting the floats,)
I'd check out the possibilty of vacuum leaks as was suggested. I would also get into the timing to be sure it's set correctly.
Unless you have a large cam with lots of duration (and nothing physically messed up with the carb) you should be able to have an idle speed of 800-900 in park and around 600 in drive. I have a 670 Street Avenger and a 276 degree cam. My idle is a described.

http://www.holley.com/data/Products/...10219-3rev.pdf

hectre13

iTrader: (4)

I think my carb might be jacked up or something.. because I have it connected to the ported vacuum.. and when the car is idleing and i disconnect the distributor... the idle goes down.. so that leads me to believe it is advancing the timing at idle.

skinny z

That would be the case if your throttle blades where open to the point where the ported vacuum is coming into play.
Have you checked your timng with a timing light?

hectre13

iTrader: (4)

I havent checked it in awhile, I can check it later when I get home from work.

hectre13

iTrader: (4)

Also if you were wondering the engine setup.

It's a 350 small block chevy out of an 88 suburban, bored .040 over, with flat top hypereutectic pistons, moly rings, bimetal bearings, high volume oil pump, and all ARP fasteners. Stock rods and crank. Stock LO5 (193) heads rebuilt. Valvetrain is a Proform gear drive, a Comp Thumpr Cam (flat tappet hydraulic 279TH7), Summit one piece chromemoly pushrods, Crane gold race 1.5 full roller rockers, and Crane springs. Induction is a stage one Summit intake with a Holley 670 Street Avanger (vacuum secondaries). Also have Headman Elite HTC headers and a MSD pro Billet HEI Distributor.

skinny z

My understanding is the Thumper line of cams has more overlap (for the choppy idle sound) then a typically spec'd cam. That may lead to idling problems on it's own. I've resorted to the old tried and true method of drilling small holes in the primary throttle blades so as to allow the idle speed screw to adjusted to a more closed position when tuning engines that have high overlap cams.
Check out post #6 in this link.
http://www.nastyz28.com/forum/showthread.php?t=181780

onebad82z

iTrader: (7)

I have seen different combos want manifold vacuum and some want ported. In my experience the car will tell you what it wants by trying both out. I would recommend to start with trying manifold in the OP's situation based on cam specs. Cam is going to want some timing to idle stable.

I think skinny z is on to something here. You have the throttle plates open to far pulling in the vacuum can at idle by uncovering the ported source, as well as starting to activate the main system in the carb as you see the booster pulling fuel. You put it in gear and load the motor down and the vacuum level drops taking timing out and the rpm's drop way down. She idles like $hit.

Sounds like you need to backup and star over. Make sure the float levels are good as it is installed right now. Then, take the carb off and ensure it is set to Holley spec. Ensure the transfer slots are .020 - .040" showing. Since it is vacuum secondary and not easily adjusted on the car set the primary side to show .020" and the secondary to .040". We know the float levels are good. And from the descriptions it sounds like nothing else has been tinkered with. Put all pump cams and squirters back to spec. Idle mixture screws 1.25 turns out from gently seated.

Reinstall the carb.

With the timing as is… connect the distributor vacuum hose to the manifold fitting on the carb. With the throttle plates set as suggested above you should easily tell which source is ported (should be no vacuum at idle) and manifold (WILL have vacuum at idle) once the car is running or check the link supplied to Holley (above also from skinny z) for diagrams. Connect vacuum advance to manifold.

Does it run? Don't touch the idle speed screws till it fully warms up.

Now the 1st thing to do if the car will at least idle is get the timing set. With the MSD HEI I would suggest to install the black 18* bushing and the heavy silver / light silver spring set (curve C in MSD papers). Set initial timing at 18* (no vacuum advance connected). Then factoring in the timing added by the vacuum can connected to manifold you should see around 36* at idle. From my experiences most MSD supplied vacuum cans add 20*? This is as viewed with a timing light. If all this adds up, disconnect the vacuum advance and plug the carb port. Now make sure you have 36* timing at higher rpm's…. 3000-3500. It should not change once revved over 3000-3500 or so. Wing it a few times to ensure. Now you have the basic "street machine" timing curve that will improve most any cars manners with a long duration cam. Reconnect the vacuum hose to the dizzy.

Nest step will be to warm the car up to a hot idle… usual coolant temp for your ride. I find it is even better to drive it around for awhile to really heat the entire car up such as a good 1/2 hour ride. Then pull off into a parking lot and connect a vacuum gauge to a manifold source just like the vacuum can. I use a T off my vacuum advance hose to be able to hook up the gauge. Now tune the IM screws to achieve highest vacuum. At this point you should have a car that runs pretty damn well and is a good point with a solid enough "base tune" that you can now evaluate what it wants/needs/requires to run as you desire it to.

Without the basics nailed down you are chasing your tail. Get all this squared away and we can help you get it better dialed in. You need to dig in, keep notes of everything you did and the results… like…. IM screws: 1 turn out for best vacuum, car prefers 34* at idle vs 36*, stuff like that. As specific as you can be on every little detail will help us better help you. You have a decent match of parts that makes for a fun street car. Now it requires YOU to tune it as a package to be able to fully utilize it.