Custom 454 won’t idle.

[Schurkey]

Perhaps a moderator will move this thread to the "LSX + Carb Swaps" sub-forum.

 

[Cookscustoms]

I was thinking the same thing re: the valve lash. Along those lines, I'd be interested in what a compression test
would give us? (ie: lower than expected compression = valve lash too tight = idling issues?

The plugs: They are showing rich / loaded up?

The carb: We have 2 separate concerns going on. First, we have to get the fuel bowl
filled to the correct level, but at the same time we don't want to send more pressure
than the float + needle + seat can maintain positive control over. I know that Quadrajets
don't like more than 5 psi maximum? I have to defer to Hipster on what the edelbrock
carb wants, but I'll bet that his recommendations are on the money. (Carbs like adequate
volume at low pressure, but they can't control high pressure at all given the needle & seat
with only a float to push back against the incoming psi. (!)

You know, pulling together the carb & spark plug reading discussions together, it doesn't
matter if you have a carb with a good float setting and too much PSI being fed to it OR
the right fuel pump pressure being fed to a carb with a too high float setting and/or there's
dirt/grit preventing the needle & seat from closing completely. Either way, if you have fuel
coming out the main venturis while the engine is idling then it will be so rich that the engine
can't idle unless you give it a fair amount of throttle. (To match the excess fuel.)

Q: Is there any way you can temporarily substitute a 'known-good' carb onto the top
of this engine? Doesn't matter what it's dialed in for, just need to be able to verify
that the 454 can idle correctly, get the initial timing set, ensure that it can take a
quick winging without backfiring, etc.

And if you don't have that, then do you have a 'known-good' engine that you can
temporarily run with this new carb on it? I don't care if it's a 302, 351W or 390FE motor,
just need a happy motor that we can verify that it will idle, accept winging the throttle
without backfiring, the float level is correct, etc.

From out here in upstate NY, I think that you are trying to troubleshoot through 2 or
more problems at once. But with a known-good carburetor I'm sure that everything
will quickly fall into line with the rest of your 454.

Good luck, and let us know what you find. Standing by --

I will do a compression check in the morning as well as try to get a vacuum reading. This carb is brand new however, I have also put a slightly used carb(750) that was too much for another truck about four months ago onto this truck, as well as a 670 Holley that I know worked great on a Ford 351 earlier this year. As far as the timing goes the only thing I’ve been able to do, I advance my timing light 32° because I can only time it while it’s revved up so while doing that at about 3000 RPM my harmonic balancer reads zero. I haven’t been able to check what my idle timing is because I can’t get it to get below 1800 and you constantly have to be pumping the gas. I’ll post compression readings as well as a vacuum reading and hopefully everything will start to fall into place. Thanks again for all the advice.

 

[Erik the Awful]

Do you have a fuel pressure regulator? I think they only want 4-5 pounds.

I run an Edelbrock, a Carter 7 psi fuel pump, and a cheap Holley 12-803 4-9 psi fuel pressure regulator in my Jaguar. When I had the FPR in my Nikki-carbed RX-7 I ran the 2-4 psi spring, but to run the Edelbrock needs the 5-7 psi spring, adjusted down to around 5 psi.

With the fuel pump running but the engine off, does the fuel pump overpower the needle and seat in the bowl? Check to make sure there isn't fuel dribbling down inside the carb.

use something other than an edelbrock

The Edelbrocks are a good carburetor for street driving. It's just a modern Carter AFB. They typically run well right out of the box unless your engine is radical. I'd suspect the fuel delivery over the carburetor.

 

[95burban]

I run an Edelbrock, a Carter 7 psi fuel pump, and a cheap Holley 12-803 4-9 psi fuel pressure regulator in my Jaguar. When I had the FPR in my Nikki-carbed RX-7 I ran the 2-4 psi spring, but to run the Edelbrock needs the 5-7 psi spring, adjusted down to around 5 psi.

With the fuel pump running but the engine off, does the fuel pump overpower the needle and seat in the bowl? Check to make sure there isn't fuel dribbling down inside the carb.


The Edelbrocks are a good carburetor for street driving. It's just a modern Carter AFB. They typically run well right out of the box unless your engine is radical. I'd suspect the fuel delivery over the carburetor.

You’re correct. I’m just more of a mechanical secondary 4150 guy.

 

[texas tough]

its either very lean or your timing is off, maybe both,.., set the base timing with a timing light.. it doesnt have to be running, it just has to fire the plugs.. once u get it timed, start to slowly enrich your idle circuit on the carb,, once u get it idling fine, then tune the throttle response.. running lean is very risky, I wouldnt drive it anywhere with it lean. you can burn thru a piston in short order..

 

[Cookscustoms]

I run an Edelbrock, a Carter 7 psi fuel pump, and a cheap Holley 12-803 4-9 psi fuel pressure regulator in my Jaguar. When I had the FPR in my Nikki-carbed RX-7 I ran the 2-4 psi spring, but to run the Edelbrock needs the 5-7 psi spring, adjusted down to around 5 psi.

With the fuel pump running but the engine off, does the fuel pump overpower the needle and seat in the bowl? Check to make sure there isn't fuel dribbling down inside the carb.


The Edelbrocks are a good carburetor for street driving. It's just a modern Carter AFB. They typically run well right out of the box unless your engine is radical. I'd suspect the fuel delivery over the carburetor.

I’m going to put a regulator in this morning. Thanks to several of you for the psi tips.

 

[Cookscustoms]

Here are my compression results from this morning also I was able to just feather the throttle enough to keep it rough idling around 600-800 rpm and the highest vacuum reading I got was 8. Thoughts??

You must be registered for see images attach

 

[Cookscustoms]

its either very lean or your timing is off, maybe both,.., set the base timing with a timing light.. it doesnt have to be running, it just has to fire the plugs.. once u get it timed, start to slowly enrich your idle circuit on the carb,, once u get it idling fine, then tune the throttle response.. running lean is very risky, I wouldnt drive it anywhere with it lean. you can burn thru a piston in short order..

Based on how black all the plugs were this morning I’d say it’s rich plus the inside of the brand new carb is already black like it’s one of my old used ones.

 

[Supercharged111]

So you got a vacuum reading of 8 which is merely an indication that the motor is struggling to run at all. If your timing is in the ballpark it's not what's causing this or the backfire through the intake, that's only if it's way off. Have you gotten the engine up to temp? It should be easier to work with at operating temp. I've got a q-jet that backfires through the intake on tip in when cold. I'm going to use a piston stop to verify the accuracy of the factory balancer's markings before ripping my hair out over timing, but I also welded in an O2 bung so I can hook up a wideband and make short work out of getting the fueling sorted. Any time I back out the APT screw it gets happier, and jetting the mains up made it happier too. Thing stinks pig rich and spits raw fuel out the tailpipes until it warms up. It doesn't have any vacuum when it's cold and sucks the needles up out of the main jets. Same thing yours is doing with only 8" of vacuum. It has a comp 256 cam in it (454) and idles around 450 until it gets some heat in it. I'm convinced when I finally get off my ass and put a day or 2 into it I'll have it running like a top.

 

[Hipster]

I will do a compression check in the morning as well as try to get a vacuum reading. This carb is brand new however, I have also put a slightly used carb(750) that was too much for another truck about four months ago onto this truck, as well as a 670 Holley that I know worked great on a Ford 351 earlier this year. As far as the timing goes the only thing I’ve been able to do, I advance my timing light 32° because I can only time it while it’s revved up so while doing that at about 3000 RPM my harmonic balancer reads zero. I haven’t been able to check what my idle timing is because I can’t get it to get below 1800 and you constantly have to be pumping the gas. I’ll post compression readings as well as a vacuum reading and hopefully everything will start to fall into place. Thanks again for all the advice.

It should have idled with one of those carbs on it.

Here are my compression results from this morning also I was able to just feather the throttle enough to keep it rough idling around 600-800 rpm and the highest vacuum reading I got was 8. Thoughts??

You must be registered for see images attach

Less than 10% between all cylinders, all good.