car stalls at full throttle????

[68chargerboy]

off the line the car rocks at quater to half throttle, but if i bury the pedal from a dead stop it backfires and dies  i am pretty sure its a timing problem but should i advance it or retard it? or am i wrong and is it the carb?  thanks

Zach

[Ghoste]

Going lean at WOT.  How is your acceleration pump and what kind of carb?

[68chargerboy]

its a holley street avenger 770

[Ghoste]

Was it working properly before and just started this, did you change anything?

[68chargerboy]

only about 20 miles on the build so i guess its always done it lol

[Ghoste]

Is the carb new, is it properly tuned?

[68chargerboy]

the carb is new and i do not believe it is.  i tuned it untill i had the highest vacuum possible at idle then backed it off a little bit and thats it

[Ghoste]

I'd start with the accelerator pump then.  Check which cam it has and that it's properly set up.  Even though it's a new carb I'd still check the float levels too.

[68chargerboy]

alright so richening it up would not help at all? also it has the vacuum secondaries maybe i should change the spring in that???

[SeattleCharger]

off the line the car rocks at quater to half throttle, but if i bury the pedal from a dead stop it backfires and dies   i am pretty sure its a timing problem but should i advance it or retard it? or am i wrong and is it the carb?  thanks

Zach

 does it only backfire and die when flooring it off the line?    how about if you are moving while at higher rpms and you floor it?  does it stall out then?  or work fine?  what is your intake manifold?  what's your rear differential?  approximate tire size?   cam size? 

[Ghoste]

I don't think fatter jets or secondaries opening sooner are the issue.  If it's dying as soon as you stomp on it from a dead stop I tend to think it is in the accelerator circuit.  With the car not running, look down in the carb and work the throttle quickly to WOT and see if there is a good strong jet of raw fuel coming out of the squirters.  If there isn't, you have a big problem.  I suspect there will be a good shot but it either isn't enough or isn't timed long enough.
But I'm no expert so this could all be a waste of your time too.

[TylerCharger69]

I dunno...but I'm leaning toward a timing/cam issue.  At WOT, the backfiring, to me, seems like the valves aren't opening at the proper time.  Vacuum advance could be wrong....I dunno.....is it backfiring through the exhaust, or backfiring back up through the carb???   I could be wrong, of course....and maybe  it's getting too much fuel at WOT and flooding out.  But I'm still leaning toward a timing issue....I'm curious to see what the problem is....keep us posted!!!

[68chargerboy]

well it's back firing through the carb.  im goin to do some driving tests to see exactly when it does it.  time to open up the 440 

[68chargerboy]

so i just took it out and it runs like a champ if i roll on the throttle but if i goose it, womp it, hammer, it, etc it cuts out? any guesses?

[SeattleCharger]

  too big of carb and or carb/intake combo for the cam type and rear gears and stall combo.  That's my guess without knowing anything about your car,   

[68chargerboy]

its a 770 carb, the lift is a 484 in/ex has a 3.23 rear with at 2200 stall.  10.8 comp 30 over bore

[SeattleCharger]

cool.   must be pretty fast car.      dual plane or single plane intake manifold?  sounds like you probably  have aluminum heads with that compression, huh? 

[Joshs68]

where is everything set?
set the mix screws one and a half turns out from bottomed,
unhook the vacuum advance, and set the total timng at 34*, I leave my advance capped and dont use it, but use it if you want to.
check for vacuum leaks. do you have play in the accelerator pump arm/spring? it should be just touching no slack. sounds like its not getting fuel fast enough when you crack the throttle. when you roll the throttle it is , lighter spring in the secondaries? I dont know much about vacuum secondary carbs but it sounds like the secondaries are not coming in fast enough

[68chargerboy]

cool.   must be pretty fast car.      dual plane or single plane intake manifold?  sounds like you probably  have aluminum heads with that compression, huh? 

thanks! i enjoy it.  but it is stock intake and heads.  looking for a new intake though

[68chargerboy]

where is everything set?
set the mix screws one and a half turns out from bottomed,
unhook the vacuum advance, and set the total timng at 34*, I leave my advance capped and dont use it, but use it if you want to.
check for vacuum leaks. do you have play in the accelerator pump arm/spring? it should be just touching no slack. sounds like its not getting fuel fast enough when you crack the throttle. when you roll the throttle it is , lighter spring in the secondaries? I dont know much about vacuum secondary carbs but it sounds like the secondaries are not coming in fast enough

i will check these things over in the morning. what is the advantage of using or not using your vacuum advance?

[SeattleCharger]

  hmm, well, I don't know about your carb tuning.  A couple things come to mind. -(separate issue- that is high compression for iron heads, aluminum heads would fix that.  440 source aluminum heads are identical to eddy rpm heads, 64cc etc., you need to get better valve locks on em, search for thread about those.  you use octane booster and 93 octane gas?)
 another thing,  a 770cfm carb is pretty big.  oversize carb will act like that on any car.  you gradually put on throttle and the engine handles being floored fine once rpm's are up, but when you try and floor it off the line, it bogs down and wants to die.  So its getting enough fuel, your pump and lines etc. are fine.  Perhaps your heads and intake are the problem, not sure.  if you tune your carb to perfection, and it still does it, you probably want to go with an eddy rpm intake or other aluminum dual plane intake, and aluminum heads will probably help.   that isn't that big of a stall either, and your rear end gears are freeway gears, all this is adding to it somewhat.  I hope you figure it out, and others chime in here with help.  I only know a little and just offering guesses at possible problem.
Nate

[68chargerboy]

 hmm, well, I don't know about your carb tuning.  A couple things come to mind. -(separate issue- that is high compression for iron heads, aluminum heads would fix that.  440 source aluminum heads are identical to eddy rpm heads, 64cc etc., you need to get better valve locks on em, search for thread about those.  you use octane booster and 93 octane gas?)
 another thing,  a 770cfm carb is pretty big.  oversize carb will act like that on any car.  you gradually put on throttle and the engine handles being floored fine once rpm's are up, but when you try and floor it off the line, it bogs down and wants to die.  So its getting enough fuel, your pump and lines etc. are fine.  Perhaps your heads and intake are the problem, not sure.  if you tune your carb to perfection, and it still does it, you probably want to go with an eddy rpm intake or other aluminum dual plane intake, and aluminum heads will probably help.   that isn't that big of a stall either, and your rear end gears are freeway gears, all this is adding to it somewhat.  I hope you figure it out, and others chime in here with help.  I only know a little and just offering guesses at possible problem.
Nate

you called it with the fuel mix, and i have a couple holley 650 double pumpers laying around, do ou think that carb size would be a better fit on it?

[SeattleCharger]

that's possible, I don't know how hard it is to swap them, but that would be one way to trouble shoot this.
    you floor that 770 and a lot of gas goes into engine,  a different intake and bigger heads might increase flow the engine can handle,  that might be your choking off point in dumping in all that gas.  if you get new heads and intake, the 770 should work fine,   but for now you can try the holley 650, then when you change it up to the new stuff, it won't be a lot of extra work then to switch the 770 to the new intake, you would have to do this anyways,
    I don't know much about tuning carbs, but if you know one of the 650's is tuned pretty good, your car will launch better off the line probably.    other option is to keep trying to mess with timing and tuning the 770 before you do this.   There are some mopar clubs around here that meet once a month at a pizza joint, if you hooked up with some people they might have some carb tuning guru guy that could take a look at your setup

[68chargerboy]

ill have to try that i am going to a cruise night tomorrow, ill ask around for someone who knows what they're doing when it comes to tuning.  as for the new heads and intake, that kind of sounds like a lot of money for such a stupid problem   so hopefully i can fix it without ay of that or i can get a good deal on at least an intake

[SeattleCharger]

ill have to try that i am going to a cruise night tomorrow, ill ask around for someone who knows what they're doing when it comes to tuning.  as for the new heads and intake, that kind of sounds like a lot of money for such a stupid problem   so hopefully i can fix it without ay of that or i can get a good deal on at least an intake

with aluminum heads you can run pump gas without issue.  also lots more power with an intake and aluminum heads.  the 440source eddy copies were 900 bucks.  an dual plane edlebrock or whatever, ebay for 125-150, 
  if you don't have headers though, its almost not worth doing all that.   what goes in, has to go out,   you might be better off with a holley 650, don't know, have fun cruisin your charger