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No PCV connection on a 4160 Holley 750 vacuum secondary?

7

78 GMC Jimmy

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So I'm replacing my 1406 Edelbrock 600 CFM auto choke carb with a Holey 750 vacuum secondary manual choke carb.

I get the leaks stopped, and get her running.

Questions:

The carb only has 3 vacuum ports.
Brake booster. (big)
Time spark vacuum source (Small, hald way up the carb)
Full manifold vacuum port (Small, at base of carb).

So which one do I hook the distributor to?

Where does the PCV valve connect?

Thanks.
 
Yeah not sure what size the full vacuum port is, it should be 3/8". Looks the MBA bean counters strick again. anyway that is your only choice.
All my Holly carbs are almost as old as I am.
 
Wes Harden said:
Yeah not sure what size the full vacuum port is, it should be 3/8". Looks the MBA bean counters strick again. anyway that is your only choice.
All my Holly carbs are almost as old as I am.
Click to expand...


What are your thoughts on connecting the brake booster or the PCV to a direct manifold vacuum port? Someone said to run the PCV to the brake booster port on this carb, and then run the brake booster to a manifold vacuum port.
 
that is doable, many manifolds have 1/4" npt port in the rear runner, that could be used for the brake booster. The TH350 will need manifold vacuum too.
 
Wes Harden said:
that is doable, many manifolds have 1/4" npt port in the rear runner, that could be used for the brake booster. The TH350 will need manifold vacuum too.
Click to expand...


I gots me a manual 3 speed (4 speed granny) so I..... I aint gots me no vacuum line to the trans.

I see no vacuum ports on the intake. The fuk I sposed to do? I need Braek boost'a and I needs me some PCV suck'n!

So Hows I sposta do dat!

Damn.

I wished I still smoked me some cigarettes, cuz I would have one right now!
 
Oh, its some sort of fancy ass Edelbrock aluminum high rise intake. The knuckle head before me musta put it on. Not sure the model number.
 
If thats the case, I would get a brass 3/8” barbed “T” and tie the two together to the one port.
 
Fastereddie said:
If thats the case, I would get a brass 3/8” barbed “T” and tie the two together to the one port.
Click to expand...

Run the PCV and the brake booster off the main vacuum port at the rear of the carb?

Huh. I guess that would work, as long as the PCV doesnt reduce the sensitivity of the booster.
 
So I got the carb fully installed and test drove it. I connected the PCV to the spot that would normally be the brake booster vacuum port. I did find a plug in the manifold behind the carb, and connected the brake booster to that. Brakes seem a little better than before.

Carb questions:

Throttle is a little sticky, so if you let off the throttle slowly, it idles as 1K. If you let off the throttle quickly it idles at 500. Or if you close the throttle by hand it idles at 500. I tried Wd40 on the carb, no help. Tried more springs, which helped a little.

I adjusted the float levels to just a tiny but below the fuel level check plugs.

I adjusted the idle mixture screws to withing 1/2 to 1/4 turn of perfect.

Accelerator pump is working well.

Idles better on this Holley VS the Edelbrock I had.

When I stomp on the gas, the engine stumbles for a split second and then takes off with high power. It feels like someone briefly shuts the ignition off when you stomp the gas. When it does take off, it produces lots of power and pull really good, but that quickly tapers off and the acceleration is cut way down. It feel like you are letting up on the gas peddle, but its still wide open. So a quick stumble, hard pull and then the power fades away. Great power from roughly 0 to 30 mph, not good power from maybe 30 to 50.

The old carb did not pull as hard off the line, but produced consistent power throughout the acceleration stage from 0 to 50.

Do I need to adjust the accellerator pump?

Why does the power fade away when getting up to speed? Is the vacuum scondary not working? How do I test that?


Thanks.
 
Yes the accell pump needs fine tuning, sounds like it is close. The vac 2nd is very hard to test on the engine. Easier on the bench with a vacuum pump.
I would look to the timing 1st, even with 2 barrels it should pull well to 50ish if not more.
 
Tried messing with the timing, didn't help. The accelerator pump was not adjusted correctly, so I adjusted it. Minor improvement if at all. Definitely still an issue. Over 2500 RPM the problem is not there. So if I'm coasting at 3K rpm and I stomp the throttle it takes off. If I'm coasting at 2K rpm and I stomp it, it cuts out and then kicks in. Just like flipping the ignition off for 1/2 a second.

I tested the secondaries with the paper clip trick. They are opening, but only when I get it up to about 5K rpm, and not opening all the way.
 
is a lean mixture miss fire, you might need the larger accell pump or a different accell cam to start the squirt earlier.
 
Original carb (Edelbrock 1406 600cfm had problems. Flooding, filling block with fuel, etc. Went through it 3 times adjusting the floats etc. Could get it to work right.

Tried a different 1406, and that was not very good either.

Tried the Holley 750 vac - not good. Weird throttle issues, flooding, stumbling, etc.

All I have left is a handful of CRUSTY carbs on a shelf. Some of them have so much dust on them that they are hard to identify.

I said screw it, and grabbed a crusty old Carter 625 CFM off the shelf that had been sitting for YEARS.

Bolted it on, adjusted the idle and fuel screws, and took it for a drive.

Starts and runs excellent. Good even acceleration with instant throttle response when I stomp the throttle.


I had no idea any of those old carbs were functional.
 
78 GMC Jimmy said:
Original carb (Edelbrock 1406 600cfm had problems. Flooding, filling block with fuel, etc. Went through it 3 times adjusting the floats etc. Could get it to work right.

Tried a different 1406, and that was not very good either.

Tried the Holley 750 vac - not good. Weird throttle issues, flooding, stumbling, etc.

All I have left is a handful of CRUSTY carbs on a shelf. Some of them have so much dust on them that they are hard to identify.

I said screw it, and grabbed a crusty old Carter 625 CFM off the shelf that had been sitting for YEARS.

Bolted it on, adjusted the idle and fuel screws, and took it for a drive.

Starts and runs excellent. Good even acceleration with instant throttle response when I stomp the throttle.


I had no idea any of those old carbs were functional.
Click to expand...
Is the Carter an original quadrajet, or an aftermarket replacement.
I always liked the original carbs the best, and I would never replace them with a holley or edelbrock.
At least not on trucks
 
imiceman44 said:
Is the Carter an original quadrajet, or an aftermarket replacement.
I always liked the original carbs the best, and I would never replace them with a holley or edelbrock.
At least not on trucks
Click to expand...


The carb was an Carter AFB. Started having issues with it, so I went through it and cleaned everything, replaced the accelerator pump, and installed the spring loaded fuel valves. The damn thing flooded badly after installing, so I went through the 1406 that I was using before and installed that one. I lowered the float level even further than before. So far its good to go.
 
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