carbed out

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mikec

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Hope everyone is well, need some carb advice, ihave 73 dart with 273 , pro comp intake(faux airgap) unknown cam, 13.5" vacuum , had edelbrock 1400 carb on it after a year of jetting,rodding just couldn't get bog out of it , i am running 15 degrees advance,without vacuum hooked up ,34 degrees at 2800 rpm bog got better but couldn't mash the gas , so i bought a rebuilt holley 670 avenger at carlisle from a vendor,fouled my plugs after 5 minute idle , adjust floats,then carb floode out of front vent , float full of fuel,bought new float,back fire out the carb and mix screws make no change in rpm? pulled front bowl, took out power valve to test ,ok but gasket in two pieces top and bottom? picked up 5.5 power valve and install test carb fouled plugs again,and mix screws worked for first minute then no change when adjusting, checked primaries and secondary for closure and transfer slots closed with no idle screw adjustment , the vendor has full message on recorder and can't leave a message (should have known better) i seem to be getting fuel with idle screw backed out and butterflies closed ? power valve gasket problem? carb no good? any reccomendations for carbs demon ,holley has to be an easier way thanks for info , i want to drop kick these two carbs
 
Hold on Mike.
That 73 Dart is a pretty heavy car for a 273.This type of combo; heavy car/small engine needs special tuning parameters..
It needs compression, inherent torque, torque-multiplication, and usually, a late opening or carefully timed secondary opening.
Let's start with a compression test.I have a sneaky suspicion somebody bolted all these goodies, including the cam onto a low-compression shortblock. In which case, you are kindof in trouble......So on to checking cylinder pressure. If it's under 110, you are more than kindof in trouble. But if it's up at 150 or better, that we can work with. This combo will not wake up until the compression is decent. I'd guess 165 would be a good number, down to 150ish. Between 140 to 120,she's gonna need some to plenty of help.

Then,let's start with transmission and rear gears. Ima gonna assume it's an auto with a stock TC (low RPM) stall and probably still has the 2.76s in it? If that's true, your carb and intake, are waaay too big. With 2.7s or 2.9s or maybe even 3.2s,that engine will want a 500carb or so, on a heated intake.Your carb and intake might work with 3.9s or better, but for sure will need a loose TC.
So, if you wanna keep that top-end, start over with a 2800TC (or better), and at least 3.55s, and rebuild that Carter.
Or put the 340-AVS top end on it, with the 340 TC, and at least 3.23s.
Or take about 600 pounds out of that car!, and still the 3.23s.
Or pull that cam outta there and start over.
Or, there is one other option. A spreadbore set-up,a 2400 minimum stall and 2.94s as a minimum.

And do yourself a favor; when you get to tuning, defeat the secondaries, and tune the front first.Get the primaries working, and the accelerator pump dialed in.Then drive it around as a 2bbl for like 500 miles, getting the timing and stuff worked out. After that's sorted, then start in on the secondaries.Any other way is just madness.When you defeat the secondaries, make absolutely sure that they cannot open or fail open; No way! There is almost nothing as scary as running up some guys tailpipe while simultaneously jamming on the brakes with both feet, and reaching for the kill switch! Don't even think about neutral.
 
Might be worth double checking fuel pressure too. What kind of pump does it have? If the carb is physically pushing fuel out and you can't get the mixture under control, the carb may be seeing excessive pressure.

Long shot, and it won't fix the bog or other issues, but might explain the current range of issues. Assuming there isn't more wrong with the carb(s) than just tuning.
 
thanks for the replies , compression testing cylinders shows 140-150 , pistons are not flat tops have a dome/wedge shape from what i can see in cylinders, have auto trans with shift kit , unknown stall, 355 gears 2-1/2 duals with headers and turbo mufflers before rear wheels, i put fuel regulator on and set for 5.5 psi i heard holley power valves had some gasket issues , maybe pushing gas past power valve ? i backed out idle screw all the way car still idled slow 500 rpm and mix srews had no effect , with the edelbrock i could power brake and light the tires but it was always inconsistent, thats why holley switch
 
^^ x 2, Well at 15* you might be close.
But here's the thing.On the Holley. With the throttle blades closed, ALL of them, there is no way the engine should idle. I wonder if the secondaries are stuck/adjusted partially open, or if the choke cam is engaged. To have the curb idle screw all the way backed out, AND the mixture screws unresponsive,AND the idle still at 500, says the engine is getting air and fuel from somewhere else. And in just the right amounts.While set up as it is now, temporarily throw a rag over the secondary side to block it off. The engine should stall, proving the secondaries are feeding.That's not good.
With your manifold vacuum, I'm pretty sure the secondaries can be FULLY closed, but not sticking, so make it so. Then, make sure the choke cam is parked. Make sure the Transfer port is synced.Reset the mixture screws. And try again.
A leaking PV will usually flood the engine to a stall.

Average of 155 psi is a very good sign, as is the 3.55 chunk.So; you have adequate cylinder pressure, and a good gear. After we get this beast running, we'll do a stall test to ballpark that. And then it's tuning time.
 
well I temporarily broke the carb lol , pulled carb off to check primary secondary blade closing ,checked with flashlight and closed blade, saw some light and figured I would adjust blade loosened screws at primary blade and one snapped, so I disassembled carb so I can drill and easy out the screw, thanks for advice after I fix carb I will try to see if secondaries are problem and bump timming, choke cam is not engaged
 
Honestly, I'm going to go down this road.

The intake you have is really probably pretty wrong for this combo. It has the big ports for a 340/360 intake when you have a small port 273. Probably loosing vacuum signal to the carb pretty badly. Something like the edelbrock performer is probably better for this combo.

The next thing is the 670 carb is going to always be too big. Your original Edelbrock 1400 may have been okay other than the economy calibration. I'm not sure if you tried stronger step up springs to make the metering rods change states from economy to power faster or not, but that would help a lot if you haven't. I wouldn't run a carb bigger than a 600 on that engine. You're probably going to want something like the 570 avenger as opposed to the 670.

I agree you should try more initial timing. Get the vacuum gauge on there and try to find the timing with the highest vaccum. My 340 has about the same amount of idle vacuum you do and I run 22 up front, which is what it likes.
 
a quick update, I put the 670 avenger in a box after I disassembled for repair ,grabbed the edelbrock 1400 put 95 jets in primary and 98 secondary put 37 meter rods in with yellow springs and new accelerator pump set linkage to center hole , went from 20 advanced to 12 advance and pulled vacuum off distributer running better than it ever has, punch it from a stop and car goes no stumble, a slight stumble when cruising and hitting secondaries, but only slight , set mix screws to max idle and vacuum, then backed off 1/4 turn, my vacuum is 13.5 at 700 idle but in gear (auto)is 7 at 500 so I may change step up springs to 5 , some great advice has helped me get it running better , took her to Riegelsville pa show on sunday car ran great thanks for all the advice FABO, will have to post a burn out vid, the little 273 sounds good winding up
 
So....no stall test yet?


There is still something not working right.Loosing 200 rpm and 6.5 inches of vacuum,by just putting it in gear, is not right,especially with 12* of idle-timing.I think that TC is too tight and that intake may be hurting you.
I'm starting to think that TC is wrong for the combo.I think it needs to be a lil looser
As to the intake,I think the plenum and port volumes are too big, and, the port mismatch and lack of carb-heat are not helping the idle,off-idle, and tip-in response.I would pull that beast and swap it for a small-port dualplane, or a very-small-plenum singleplane.
Your method of setting the timing is very strange as well. I take it that you disconnected and blocked the vacuum advance, then reset the initial idle-timing from 20* down to 12*. But you make no mention of what the power-timing is, nor a hint of what the rate of advance might be, nor if you ever put the Vcan back on line.
With a less-than-optimum combo,and a lack of vacuum advance, the part throttle performance will really suffer, especially in the 1000 to 2500 range.
Glad to hear it's running better, tho
 
I still have vacuum can hooked up, I disconnected to check for leaks , it made no change in vacuum, or running, so I put back on, I set initial at 12 as a test ,motor smoothed out , re-adjusted mix screws for idle speed increase and vacuum read , I didn't check all in rpm again because It ran good enough to get to car show, electronic mopar with one lighter spring installed , I will continue to tune and test, last test of all in was 34 at 2800 I don't know if that changed with initial change to 12. I tested adding advance to 20 -24 from 15. Ran worse and was breaking up the more I advanced it. Swapping back to the edelbrock ,smaller jets,meter rods have made it run decent , I do agree my vacuum is low at idle, I have a rebuilt magnum 318 ,fresh with 512lift comp cam waiting in the wings, the intake and carb will be used on that motor, I am sure the intake is too much for the 273 but that's how it came with the car, just trying to run it till I can gather rest of parts, thanks again for all the advice. I will try to post a video of it running.
 
Ok , how's this sound; when you had the idle timing set to 15*; the all in was 34*. Is that right? If yes, then there is 34 - 15 = 19 in the dizzy. Typically the dizzy-cam will allow 20*, so you read it nearly right on.
This also means that whatever you set the initial to, the all in will always be 19/20* more. So with 12 initial, the all in will be 12 + 20 = 32. The 2800 does not change.
So far so good?
I suspect the Vcan diaphragm is ruptured.That means, as soon as you crack the throttle, the carb will suck air through the diaphragm and make trouble. Check it out. If I'm right, plug the line into the carb to prevent that.Then as time permits go get a new can.
I also feel that the timing may be coming in too fast, for your combo.I think your timing experiments are proving that. I assume these tests were not done in N/P, but on a loaded engine while driving?
 
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