Vacuum Leak???

[born2Run83]

350/TH350 with Holley 600cfm.
From 60mph and on it tends to flat line. The idle rpm (no tach installed) seems pretty low, rough and eventually dies at times when in gear with the brakes applied. I took to a local shop that does quite a bit of custom engine builds and they tuned the carb with a wideband and adjusted the timing some. The top end acceleration is better now but it’ll now eventually idle down and stall when in park (engine warm) after idling for a few minutes. At stoplights I put it in neutral otherwise when in drive with the brake applied it’ll die. I am thinking vacuum leak but could this possibly be a brake booster issue? TIA!

 

[Camar068]

you prolly did this already but just in case.....get some starter fluid spray and hose around looking for idle changes. Short squirts on anything that's got a vacuum.

 

[AuroraGirl]

350/TH350 with Holley 600cfm.
From 60mph and on it tends to flat line. The idle rpm (no tach installed) seems pretty low, rough and eventually dies at times when in gear with the brakes applied. I took to a local shop that does quite a bit of custom engine builds and they tuned the carb with a wideband and adjusted the timing some. The top end acceleration is better now but it’ll now eventually idle down and stall when in park (engine warm) after idling for a few minutes. At stoplights I put it in neutral otherwise when in drive with the brake applied it’ll die. I am thinking vacuum leak but could this possibly be a brake booster issue? TIA!

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Whats your distributor look like if you open it up

 

[born2Run83]

Sprayed around hoses and did not find any changes in idle speed.
- I will pull distributor cap off and send pic tomorrow. Work today set me back some. It accelerates well but also noticed when shifting to Reverse, it wants to die even faster then when it’s in park. Park idle lasts about 3-5 seconds now. Reverse idle less than 2 seconds. It has a mild cam and stock converter.

 

[AuroraGirl]

Sprayed around hoses and did not find any changes in idle speed.
- I will pull distributor cap off and send pic tomorrow. Work today set me back some. It accelerates well but also noticed when shifting to Reverse, it wants to die even faster then when it’s in park. Park idle lasts about 3-5 seconds now. Reverse idle less than 2 seconds. It has a mild cam and stock converter.

is this holley 600cfm a 2 barrel or a 4 barrel?is it possible you have some choke interactions like it isnt open all the way or the cfm the engine IS getting is low on volume. 600 cfm and a cam to me seems like its completely possible but maybe would require some carb tuning because Qjets, if i recall, handle with very precise engine load conditions or something and it was holleys who do vacuum? If vacuum, secondaries maybe... your truck falls into needing a more deep dive on calibration?

Im out of my waters here @Rusty Nail come here holley man your knowledge could be helpful

 

[born2Run83]

Yes it is the 4160 - 600cfm 4bbl. Pics attached.

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[born2Run83]

Brake booster check valve is good.

 

[Rusty Nail]

Hay lol....what's goin on right here?

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I count no less than three problems on this side alone. Probably 4 though and looks like 5 really.
Anybody else?

Thanks AuroraGirl

You're in the right spot old boy but let's see this alleged "truck". Needs most pix, this thread.
OR!
Pix of your ol lady will work too.

**I'm counting -no washers underneath the carb stud nuts- as one problem of the supposed five.

I'm not real sure how it runs much at all like that. Very curious indeed!
Wants a top down view no air cleaner showing all sides and connections to the carb.

Oh. Yes I see it - ty.



Got a gasket underneath that air cleaner, right?

The difference between a 4160 and a 4150 is the secondary metering block.
A 4160 is an updated 4150 see?
Please note the carburetor you posted has none rear metering block. The rear bowl is bolted directly to the carb body.
That sh*t is OLD.

It has a HUMONGOUS vacuum leak
no hose clamps.
The choke is not powered

BUT! The vacuum leak is likely your main trouble. Add a cap on that deal first. The hole behind the choke there? Ain't that your PCV line?

Also observed only one valve cover pictured and it's on the wrong side of the engine....so wtf kinda hanky stuff is goin on at the other side?
You have no PCV valve?



Moar pix pliz.

 

[born2Run83]

Thank you Rusty Nail! Installed stud washers, and rotated vacuum line 1/8 turn clockwise. Stall issue remains

There isn’t any hesitation on the fuel side when accelerating. Everything is during low idle speeds.

 

[born2Run83]

Hay lol....what's goin on right here?

You must be registered for see images attach

I count no less than three problems on this side alone. Probably 4 though and looks like 5 really.
Anybody else?

Thanks AuroraGirl

You're in the right spot old boy but let's see this alleged "truck". Needs most pix, this thread.
OR!
Pix of your ol lady will work too.

**I'm counting -no washers underneath the carb stud nuts- as one problem of the supposed five.

I'm not real sure how it runs much at all like that. Very curious indeed!
Wants a top down view no air cleaner showing all sides and connections to the carb.

Oh. Yes I see it - ty.



Got a gasket underneath that air cleaner, right?

The difference between a 4160 and a 4150 is the secondary metering block.
A 4160 is an updated 4150 see?
Please note the carburetor you posted has none rear metering block. The rear bowl is bolted directly to the carb body.
That sh*t is OLD.


Moar pix pliz.

No gasket under air cleaner, yet! I can pick one up tomorrow though. I believe this is a 2007 model 4160 so yes quite old indeed. Going off the stamp near the Venturi.

 

[born2Run83]

Hay lol....what's goin on right here?

You must be registered for see images attach

I count no less than three problems on this side alone. Probably 4 though and looks like 5 really.
Anybody else?

Thanks AuroraGirl

You're in the right spot old boy but let's see this alleged "truck". Needs most pix, this thread.
OR!
Pix of your ol lady will work too.

**I'm counting -no washers underneath the carb stud nuts- as one problem of the supposed five.

I'm not real sure how it runs much at all like that. Very curious indeed!
Wants a top down view no air cleaner showing all sides and connections to the carb.

Oh. Yes I see it - ty.



Got a gasket underneath that air cleaner, right?

The difference between a 4160 and a 4150 is the secondary metering block.
A 4160 is an updated 4150 see?
Please note the carburetor you posted has none rear metering block. The rear bowl is bolted directly to the carb body.
That sh*t is OLD.

It has a HUMONGOUS vacuum leak
no hose clamps.
The choke is not powered

BUT! The vacuum leak is likely your main trouble. Add a cap on that deal first. The hole behind the choke there? Ain't that your PCV line?





Moar pix pliz.

-3/8” and 1/4” line clamps for the hoses
-Gasket between carb and air cleaner

The line behind the open hole behind the choke is what runs to the PCV line on the driver side valve cover. I am not sure why this other one is left open! (Previous owner didn’t know much either as he wasn’t the builder)

 

[Rusty Nail]

Seriously dude.
Find us a piece of hose to stick a bolt in and plug that leak.
Might solve all your problems if that's what it is.

 

[born2Run83]

I will do that for sure. Good catch! Here are some more pics I just took

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[born2Run83]

This pic shows that open port better. It’s connected to the choke. In the 4160 diagram is shows a hose going from that port to another port just above it near the vacuum secondary assy.. but this carb does not have that. So I will plug it off and give an update

 

[born2Run83]

However, I just read up and found this port to be a cooling source for the choke. ‘It says to not plug this line. I will hose clamp everything else though and go from there.

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