Discussion in 'General Tech' started by bugzaper, Oct 19, 2018.
Enlarging the "Needle and Seat" for more fuel flow.
1. Chevy used rocker arm nut
2. Q-Jet used check ball
3. Punch & ball-peen (small) hammer
4. Black Marker
5. Hand held small vacuum pump
Drill out the hole using a drill press.
Peen both sides of hole using the ball and hammer. Don't need to beat the "Crap" out of it, just a few light taps.
Mark a used needle with black marker - insert into seat and twist lightly, this shows the new hole pattern.
Insert needle into seat and apply around 10lbs or so of vacuum - should hold a steady vacuum for a few minutes.
IMPORTANT: must get a good seal between the seat's outer threads and vacuum pump hose or you will not get a good reading!
few more pics.
Any old seat will work as along as it still seals on both the thread and needle sides.
Very important to get an exact 90 degree angle before drilling, take your time...
The one pic of needle show the ".148" seat, which is getting pretty close to the max..
Here is a pic. of the idle screws after marked with black marker and screwed all the way to stop.
It shows how much more mixture is allowed after opening up the holes.
Normally with the stock opening you'd get about half of what is now showing.
I opened these up to .093.
Also, another little trick I've used over the years on these carbs., makes them a bit more user friendly on a rebuild.
1. take out the little pin
2. tap the hole
3. use a screw to hold the arm in place
You can also grind off the little nub (see red arrow) to allow the removable of the pivot arm.
It won't hurt anything and gets another dangling part out of your way.
I can tell you are a patient man! (I'm not)
Again, nice work …. and a good trick there using the black marker to see the difference the increased hole size makes. Pretty slick! Did you come by these mods by trial and error?
Thanks for the education.
Used the "black magic marker" for many years.
First started using it (in a prior life) when I was a "Felony Mechanic Inspector" as a chain of custody tool i.e. mark - photograph - document.
Always have a few in my pocket.
One of the biggest issues I read about. Is the air horn being bent from over tightening. Many, inluding me, never check this during their first rebuild. I put a flat edge on mine and was shocked!!! Even the thick gasket wouldnt seal.
I used a palm sander with 220 grit. It took a while but i got it closer. Almost everywere touched. What didnt touch was within .030 feeler gauge.
I share this to help someone who has never rebuilt one or like me, done it and still had issues. I have yet to test as i am waiting on my air valve screws to get here. 6-32x5/16 Incase anyone needs that info too.
Q:1. When you opened up your idle adjustment screw hole to .093 did you need to shorten the spring any?
2. Did the tip of the needle stick into the carbs ventri? If so did you file it down?
3. How did you make sure the ball used to peen the is ideal?
4. Have found that a windowed seat is better or a solid is better
5. Is the .135 better all around? I see you have many that size.
1. yes, I cut off "2" coils
3. followed what "Cliff" recommended and if done properly will hold vacuum
4. solid allows the elimination of drain back - window does not, either works just as good as the other
5. .135 allows more fuel and is about as big as you want to go without using a fuel regulator, the bigger one is going into an all out effort carb.