wont idle by itself

[cwhubb]

I searched the forums but didnt find my answer... I went from a 750 vac holley to a 950hp dbbl pumper and the car wont idle with out a little manual throttle manipulation, it leaked so I took it in to have it fixed got it home today and it doesnt leak but it wont idle on its own, it runs till the bowls go dry then quits. it idled before I took it in, I have a 1 inch spacer on the stock manifold I dont have the linkage hooked up yet I'm waiting for the tall bracket kit to come in, the manifold brake booster hose is hooked up, the carb doesnt have a pcv port so it isnt connected to the carb. could it be a vac leak? it runs and idles smooth when I manually open the throttle and is very snappy when I rev iwhen it runs it idles rough cause of the cam an old school crane fire ball very close to the mp 509 cam, but it doesnt shut off, what do you think it is? btw the fuel pressure reads about 3.5 when it did idle albiet with the bad leaks

 

[J5 GTX]

First, I'm not quite following what you are trying to say.
You say "it won't idle by itself", but later say it i"dles smooth when manually opening the throttle".

How far do you have to open the throttle? Is it just a matter of idle speed adjustment.? I'm just trying to get a better picture of what's happening.

Also, you say it "runs til the bowl goes dry". That's normal.

The bowl shouldn't be going dry.
Again, not trying to be insulting or anything, just some clarification.

As far as Holley Dbl pumpers go, I've never had one behave well for a street engine.

 

[cwhubb]

no offense taken when I say it wont idle by itself I mean pump the gas once turn the key it starts right up then after 3 seconds the engine stalls. when I manually hold open the throttle the engine will run fine as long as I keep it reved around 1,200 rpm ? thats just a wild assed guess I dont have a tach. I turned the idle screw in, it idles faster but it still runs out of gas if I dont manually work the throttle. I know the bowls arent supposed to run dry, what I'm trying to figure out why thats happening, I'm wondering if the fuel pump is to wimpy at idle to feed the carb. when I goose the throttle it revs nice and snappy no farts,burps or stumble

 

[bandit]

3.5 fuel pressure sounds too low. I'm pretty sure stock pressure to the carb is 5.5-6.

 

[cwhubb]

@ bandit thanks, the 950 uses a 3/8ths fuel line fitting and to me it looks like the fuel log/carb tube is a bigger diameter too, dont know if that makes a difference as far as fuel psi requirements go

 

[bandit]

Maybe, but with that size carb you should probably be looking at an electric fuel pump with an inline fuel pressure regulator anyways, if you don't have one already. If your going to open that up, you might need to up the pressure past the standard 5.5-6. You must be racing it.

When I bought my Charger, the previous owner raced the 1/4 mile with it and had the 750 Holley fuel pressure set at 8 psi. Burned your eyes at idle though.

 

[cwhubb]

It's mainly a street car, they actually have pretty good street manners, you have to remember variables, I live at 6300 ft my motor needs air, I jet down the carb so it runs leaner, I have a bigger cam, heads are ported, higher than stock cr, high rise duel plane intake, gears, converter.it would be way too big on bone stock engine

 

[bandit]

That would definately be a need for that size too.

I still think your fuel pressure is a problem at 3.5. If your running a mechanical pump I would just swap it out. They are easy enough to do and cheap.

 

[cwhubb]

I'll double check the pressure and see where that leads, thanks Bandit

 

[cwhubb]

pressure is at 5

 

[krowbar]

Fuel filter plugged up? Floats adjusted properly?

 

[cwhubb]

@ krow I'm almost positive its the fuel pump, the pressure went up to 6 and it idled by itself, then dropped back to 3 and crapped out, it had sat for quite a while so I bet it went tits up

 

[J5 GTX]

If it will run fine at 1200 rpm , you certainly have enough fuel supply to run at idle.
Assuming your fuel pressure remains constant.


3.5 is low, but it should be plenty to idle the engine. 6300' elevation is a real consideration.

- - - Updated - - -

When you pump the gas and it runs for 3 seconds, is because the engine is running off the accelerator pump shot.
At 1200 rpm~ (wag), the carb. is off the idle circuit, you are on the transfer circuit or maybe even the main jets.
How many turns out do you have the idle mixture screws?

- - - Updated - - -

With that elevation, a lumpy cam, 3.5 psi pump pressure, maybe there isn't enough of a fuel supply and/or vacuum to draw fuel through the idle circuit.
Do you have a vacuum gauge? Just curious what kind of manifold vacuum you are pulling?
Getting kind of on the edge of my experience, particularly with big Holleys.

You goose the throttle and it responds properly: at least the accelerator pump is functioning.

 

[cwhubb]

I was way off on the 1200 rpm guess, its way more than that, the cam isnt extreme enough to give me vacuum problems, it ran ok with the old carb, the only new variable is the bigger carb I went to. I ordered a new fuel pump so we'll find out the problem soon as I get it in

 

[62MAX]

I was way off on the 1200 rpm guess, its way more than that, the cam isnt extreme enough to give me vacuum problems, it ran ok with the old carb, the only new variable is the bigger carb I went to. I ordered a new fuel pump so we'll find out the problem soon as I get it in

\


Out of curiosity ,why did you go to the 950 if it is a street car and ran OK before ?

 

[cwhubb]

@ 62max the 750 was leaking very badly, I needed a new carb anyway and I'm up grading to rpm heads and a 557 lift solid cam so I'm going for more cfm across the board, plus if it's properly jetted its decent for the street, I'm @ 6300ft and can use the extra air

 

[cwhubb]

update, wasn't the fuel pump, called my carb guy and he said almost all idle problems on a good carb are vacuum leak related. found a small chip on my phenolic spacer where the carb bolt goes through. stay tuned

 

[cwhubb]

the carb idles now, i replaced the cracked spacer