'70 Valiant 4bbl carb ( it came with the car) .
The car has been running fine for 2 years now.
My son is coming home from work, the car dies as he takes his foot off the gas to coast.
OK what's happening is the vacuum line from the carb to the PVC is pulling so much vacuum that it's Pinning the PCV valve so it's choking out the engine.
Thought maybe the PCV went bad. Nope, new one acts the same. I ran a screw in the top of the PCV to adjust it from closing and car runs good.
Any ideas? this came on so sudden.

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1970 Valiant.. my sons Daily Driver
1975 CJ5, fiberglass body,350/345Hp chevy
1985 chevy stepside pickup, Original Owner
1989 Volvo 240: Original Owner
OTHER TOYS: http://home.no.net/ebrox/Tony's%20cars.htm

What a novel way to get around adjusting the idle speed and mixture.

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Joshua

The PCV valve is not choking out the engine. It's supposed to be almost totally closed off like that at idle. If it weren't, the correctly-adjusted engine would see a giant vacuum leak via the PCV valve at idle, and it would not run.

Throw away the PCV valve with the screw in it, install a replacement PCV valve (and leave out any screws or other hardware items), then go here and read up on how to adjust the idle mixture and speed.

Tune-up parts and technique suggestions in this thread.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

No, you all are missing the point. To put it simply. If I plug off the Manifold vacuum, the car stalls immediatly.

I don't get this. I should be able to just plug that hose If I wanted to and throw the PCV away. not the case. With that hose plugged car does not run. why doe sthis car need this huge vacuum leak. As I said .. one traffic light the car was happy, next time he was at low idle, car died. and now we have this.

The screw in the PCV is to force it open at low idle so the car will run.

_________________
1970 Valiant.. my sons Daily Driver
1975 CJ5, fiberglass body,350/345Hp chevy
1985 chevy stepside pickup, Original Owner
1989 Volvo 240: Original Owner
OTHER TOYS: http://home.no.net/ebrox/Tony's%20cars.htm

Will need more information about your car. What carburator, what manifold, what's you vaccuum reading at the carb? Did the previous owner leave any info about how he built the engine?

If the engine is dying wihtout a vacc leak then it is probably too rich... after two years the engine would need a valve lash minimally, and if it's a holley 4 barrel I'd bet the power valve has ruptured and it's too rich in the mix and needs the extra air to keep from choking out....

What it the color on the electrodes of the spark plugs after you "choke" the engine out?

The car has been running fine for the 2 years we have been driving it. It's my sons Daily Driver. So this problem is not something that came with the purchase of the car. It just happened.

Holley 4160-8007 4 bbl
Offy Aluminum manifold.
I believe the car is stock after that. Judging from the Burnt intake valves and the rockers being adjusted too tight when we bought the car, I think the P.O. just threw a 4bbl on a stock engine.

Power valve too rich. Hmmmm
Will I see a physical problem if I take that off? How can I tell it's bad. broken spring? Is there a part number so I can get the correct size stamped on it? I see NAPA only sells two different ones.

_________________
1970 Valiant.. my sons Daily Driver
1975 CJ5, fiberglass body,350/345Hp chevy
1985 chevy stepside pickup, Original Owner
1989 Volvo 240: Original Owner
OTHER TOYS: http://home.no.net/ebrox/Tony's%20cars.htm

The power valve is in the primary metering block. There is little to see there. Simply replace it with a new power valve of the same size.

If the power valve has failed, check to see if the carb has anti-blowout protection installed. If not, purchase the kit, and install it.

If you decide to go through the carb, stick with the Holley rebuild kit for best results. Other aftermarket kits do work, but are not recommended.
While in there, find out what jets are in use, what metering plate on the secondary, or jets in the secondary block if the PO installed the metering block conversion. These can be good things to know on down the road.

In "from the factory" form, and 8007 will not be set up correctly for a slant six, and there are many other setup parts that will need to be addressed for driveability issues.

CJ

On the slant, first it's important to know what your idle vacuum is. Check this in gear at idle in an automatic car.

Once you have that information, you'll know more about the overall health of your engine and state of tune. You should see between 19 and 20 inches of HG.

Go get a 10.5 power valve for the slant. For a stock driver, it works pretty well. If you find you have considerably less vacuum in your test, find out why.

Valve adjustments are the big killer. On the other hand, a low compression engine with lots of cam will exhibit low vacuum readings.

At two years of daily driving, your due for a valve adjust anyway. If you've been raining gasoline down the bores for any period of time, your rings are shot. Don't drive it in this condition.

CJ

The higher the number, the longer it stays closed? Delivers fuel slower?

Stock 8007 comes with a 6.5... I just found a website
http://www.mortec.com/carbs.htm
Should I down jet this?

The vacuum sucking my finger at the manifold could lift a small boy. Although I did not put a gauge on it.

_________________
1970 Valiant.. my sons Daily Driver
1975 CJ5, fiberglass body,350/345Hp chevy
1985 chevy stepside pickup, Original Owner
1989 Volvo 240: Original Owner
OTHER TOYS: http://home.no.net/ebrox/Tony's%20cars.htm

The higher the number, the sooner the enrichment comes in when the vacuum drops out. (During acceleration.) 10.5 is the earliest enrichment you can get in a standard flow PV. Don't use a dual rate. It won't work well in this application.

A 6.5 is way to late. And yes, that's what comes in it. Your primary jets should be ~52 or 54's to be jetted right to a stock 225.

A WAG on the plate is a 39, which is a tad rich, but it's unlikely your getting much out of there if the secondary spring hasn't been addressed. Depending on what was shipped, you may find that a purple secondary spring works pretty well. I'd be willing to bet that isn't what is in there.

The accelerator pump cam should be the Pink or the Orange, depending on your build. Stock, stick with Pink in screw position #1. Take a look at the pump shooter. Once again, WAG for 28ish.

Tuning a Holley four barrel can be done reading plugs. I prefer an A/F meter, tach and vacuum gauge so I can see what is going on.

With a stock engine, a 4 bbl Holley, even the small ones, need to have the circuits band-aided to the application.

On the bright side, I got considerably better economy when I was futzing about with a 390 Holley on my basically stock build. Much better than anything the old Holley 1945 ever thought of delivering in my fat old Valiant. If you are running a 4 bbl, you really need to get your compression into range. 9:1 is a nice number. Anything under 8:1 it's not going to provide you with any performance advantage.

2¢

CJ

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Part of Tyrde-Browne Racing

So you need a vacuum leak to make the car run. Adjust the carburetor curb idle and idle mixture.

I once made my Dart run with that PVC port wide open. As soon as I plugged it, as it should have been plugged, the engine died. Closing down the idle mixture screws which were adding enough fuel to compensate for the vacuum leak and opening the throttle plates by adjusting the curb idle restored proper function.

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Joshua

When we first got the car it was a none runner. Sat for years.
I bought a fuel bowl gasket and a 108-28-2 Metering Block for the Secondary. I got that info off the internet this 108-28-2 is supposedly for Chrysler setups. But that was my extent of Playing. The idea was to clean the fur out of the carb and try to get this thing running. It's a $200 car on a 17 year olds budget. So it was not meticulously looked at, it was made to just run reliably.
Yes, it bogs on hard accel. So if you had some Jetting suggestions along with the Power valve you suggested, I'd throw those in.
The Engine, Could probbaly use a Head job. We took it off after we saw horrid compression and found a few Exhaust valves burned. We bought new, Lapped them in and called it a day. That brings me back to teh Power valve. You say 10. the stock is 6.5. Where should I lean for a tierd engine?

_________________
1970 Valiant.. my sons Daily Driver
1975 CJ5, fiberglass body,350/345Hp chevy
1985 chevy stepside pickup, Original Owner
1989 Volvo 240: Original Owner
OTHER TOYS: http://home.no.net/ebrox/Tony's%20cars.htm

First things first. Find out what the vacuum is actually reading. Where are the mixture screws and idle adjusted too? Dial them out to 1-1/2 turns and turn the idle screw in a bit and try again. If it still misbehaves, start going inside to find out what's broken.

If you want to stop messing with the thing, order a 500 cfm Edelbrock, bolt it on there and be done with it. The Edelbrock will run very well right out of the box.



CJ

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Part of Tyrde-Browne Racing

The idle screws are where they belong. 1.5 -2 turns out. We did that when we first gor th ecarbs cleaned. To get me back to running... I will pull the Power valve and replace with the same #. Then I can go and check Vacuum at idle in gear and go from there.
Thanks

_________________
1970 Valiant.. my sons Daily Driver
1975 CJ5, fiberglass body,350/345Hp chevy
1985 chevy stepside pickup, Original Owner
1989 Volvo 240: Original Owner
OTHER TOYS: http://home.no.net/ebrox/Tony's%20cars.htm

Thanks Everybody. I replaced the PV and we are back to a running car. I guess a PV can crash hard and fast. They obviously can pour enough gas down the Manifold to stall a car but run nicely with a huge manifold leak.
Anywho... now we have a baseline and We an look at the real vacuum at the manifold and look at rejetting. etc. We put the PV in, warmed the car up adjusted the Valves and my son just had time to get to Work.
You really think an 8.5 or even a 10.5 would make the car happier? I thought it was over carb'd and the later the gas flows the better.
I have a box of accel Cams from my Jeep Holley. I will look at how the Accel Pump responds.
Honestly, I have never had any luck tuning in an aftermarket Carb. The Jeep still has issue. That has a .5"+ cam in it so vacuum is low.
Thanks again.

_________________
1970 Valiant.. my sons Daily Driver
1975 CJ5, fiberglass body,350/345Hp chevy
1985 chevy stepside pickup, Original Owner
1989 Volvo 240: Original Owner
OTHER TOYS: http://home.no.net/ebrox/Tony's%20cars.htm