power piston
Thread Starter
Instructor
Joined: Nov 2012
Posts: 124
Likes: 3
power piston
Is anyone familiar with tuning the power piston with a rod on the bottom by adjusting the screw in the base plate? I've read that for this to work correctly you must open the plugged air bleed holes. My questions are, are they the holes next to the primary rods or the ones at the back of the bowl ? How do you open them without damaging anything?
Any info is appreciated.
Fred
Any info is appreciated.
Fred
Race Director
Joined: Jan 2000
Posts: 13,011
Likes: 2,249
From: Corsicana, Tx
2020 C2 of the Year - Modified Winner
2020 Corvette of the Year (performance mods)
C2 of Year Winner (performance mods) 2019
2017 C2 of Year Finalist
All you're changing is the height of the metering rods when there is high vacuum and they are held down in the jets.
A little goes a LONG way on that setting. Don't get crazy with it.
JIM
A little goes a LONG way on that setting. Don't get crazy with it.
JIM
Pro
Joined: Nov 2008
Posts: 680
Likes: 5
From: Denham Springs LA
I didn't think the 71 carb had the adjustable power piston. I could easily be wrong, but I thought early carbs were not adjustable, then somewhere in mid 70's they added the adjustment capability. I remember reading a paper by Lar's that showed how to adjust/set it. I would email him and ask for that paper.
There are also two lengths of metering rods for the primaries. Maybe you have the wrong ones. I am in the middle of working on the qjet for my 71. The metering rods for the 71 qjet are 2.47" long.
Be careful, when I bought my car someone had replaced the original carb with one from a late model Pontiac, so nothing was correct. I found the correct carb and am now going through it.
Why do you need to adjust the metering rods?
I believe all you can do with the 71 qjet power piston is change the spring that's below it. With the engine running you can stick a small screwdriver down the float bowl vent tube and see if its all the way down. If you have too strong of a spring, the vacuum can't pull the power piston all the way down.
Roger
There are also two lengths of metering rods for the primaries. Maybe you have the wrong ones. I am in the middle of working on the qjet for my 71. The metering rods for the 71 qjet are 2.47" long.
Be careful, when I bought my car someone had replaced the original carb with one from a late model Pontiac, so nothing was correct. I found the correct carb and am now going through it.
Why do you need to adjust the metering rods?
I believe all you can do with the 71 qjet power piston is change the spring that's below it. With the engine running you can stick a small screwdriver down the float bowl vent tube and see if its all the way down. If you have too strong of a spring, the vacuum can't pull the power piston all the way down.
Roger
Le Mans Master
Joined: Jul 2006
Posts: 8,117
Likes: 104
From: charlotte north carolina
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
2027 Corvette vs The World: Every Model vs Closest Competitor
Joe Kucinski
10 Most Common Corvette Problems of the Last 20 Years!
Joe Kucinski
5 MOST and 5 LEAST Popular Corvette Model Years in History!
Joe Kucinski
2027 Corvette Buyer's Guide: Everything You Need to Know!
Joe Kucinski
10 Things C8 Corvette Owners Hate (But Won't Tell You)
Joe Kucinski
10 Best Corvettes Coming to Barrett-Jackson Palm Beach 2026!
Brett Foote
Every Corvette Grand Sport Explained! (C2, C4, C6, C7, & C8)
Joe Kucinski
Grand Sport & Grand Sport X Launch Alongside All-New 535hp LS6 V8!
Michael S. Palmer