FAT carb

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kocuda

kocuda

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I have a 850 Quickfuel carb. Its running extremely rich. I mean if its running in the garage for any time even with both doors open your eyes begin to burn. It has no adjusment with the mixture screws. Float levels are correct, secondary throttle plates are shut.
Could the power valve be blowin? And if so I have 5 inches of vacuum at idle, would I use like a 4.5 power valve?
Need a little input!
 
Why does it not have idle mixture screws?

You need to go 2 numbers down from your idle vacuum. So you need a 3.
 
it does have idle screws, they just dont have any affect when I adjust them
 
If you remove the carb and check the primary transfer slots,are they completely exposed? or just a small amount,if so your idle curcuit needs to be redrilled to allow more fuel through the idle curcuit,as you are running on the transferr curcuit and you most likely have a blown valve as well.This will allow you to close the throttle blades and the idle curcuit will start working again,mrmopartech
 
how big is the cam?

more then likely you have the idle set too high...and the mixture screws have no effect since the transfer slots are exposed;;;;

and make sure you timing is set correctly......
 
Its a flat tappet cam. intake lift 563, exhaust 585, duration intake 300, exhaust 310
 
How much timing are you running initial and total? Start here first then we'll move on to the carb.
 
Most carbs come with 6.5 power valve.(TAKE IT OUT)

When you run a engine with that big of a camshaft, you have to use a 2.5 power valve.
You said you have 5 inches of vacuum at idle,SO THERE'S YOUR PROBLEM.
YOUR DUMPING ALL THE FUEL YOU WOULD USE ,IF IT WERE AT FULL THROTTLE, IN THE ENGINE AT IDLE.(very rich indeed)

Change your power valve to a 2.5 and set your mixture screws one full turn out to start.
Use a vacuum gauge and try to get the highest reading of vacuum at 1000 rpm's.
1000 rpm's is not to high of a rpm with your camshaft and for the best street manners you might want to set it at 1100 in park and 950 when in drive.
When it is set up right, it will only drop a little rpm when put into gear.
The least amount of rpm drop is desired when going from park to drive.
GOOD LUCK :burnout:
 
4 corner idle? What's the duration at .050?

Make sure the slot is slightly exposed on the secondary as well. The secondaries can not be completely shut.

Open the secondaries so you can close up the primary side.

Vacuum will likely increase as you clean up the rich idle. I wouldn't worry about the PV selection right now. You might even put a plug in it just to get a clean idle, removes another potential variable. Get the blades reset and then tune it up.
 
what was the deal with drilling holes in the throttle plates? was it just a backyard type of fix??
 
up date,
I took the carb apart, it had a 4.5 power valve in it. I installed what I could find quick a 3.5. Its better, not great. Next thing I will do is open up the secondary plates, they were open a bit and I thought that was a problem and adjusted them closed. It is a 4 corner adjustment carb, I will adjust the secondary plates and readjust the mixture screws, oh and order a 2.5 valve. The rear metering plate has a power valve plug in it.
Next I noticed it had # 78 jets in the primary and secondary metering plates, isn't that a little big for the primary?
 
inkjunkie said:
what was the deal with drilling holes in the throttle plates? was it just a backyard type of fix??
Click to expand...


By drilling holes in the plates it allows more air into the motor. By letting more air into the motor you can now close down the throttle plates to get the carb back on the idle circuit.

Some Holley carbs (mostly two barrel) actually come with holes already in the plates.


Chuck
 
Use 74 jets in the front and 84 in the rear to start.
This is a good place to start jetting a big block.

The four hole spacer i suggested will make the car idle better in drive and run smoother from a dead stop under all driving conditions.8)
 
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