Mechanical fuel pump question
Thread Starter
Melting Slicks
Joined: Mar 2006
Posts: 2,465
Likes: 0
From: Orange Park Fl
Mechanical fuel pump question
My Q-jet started gushing fuel the other day. I assumed the needle/ seat was the problem. Opened the carb, and indeed, I had gotten some bad gas somewhere and had rust colored sediment in the float bowl. I took it apart, cleaned and rebuilt it, installing a new needle/ seat and a new fuel filter. The nitrophyl float seemed fine (it's not but a couple of years old).
I put it all back together correctly (I know what I am doing), and when I started the car, the carb immediately filled with fuel and was gushing again. I took off the airhorn and everything looks fine.
My question is this: Could my mechanical fuel pump have suddenly started pumping at a higher pressure? I have never heard of this happening, nor can I think of what may cause it, but the possibility that two needle/ seat valves are bad seems unlikely.
Thanks and God bless, Sensei
I put it all back together correctly (I know what I am doing), and when I started the car, the carb immediately filled with fuel and was gushing again. I took off the airhorn and everything looks fine.
My question is this: Could my mechanical fuel pump have suddenly started pumping at a higher pressure? I have never heard of this happening, nor can I think of what may cause it, but the possibility that two needle/ seat valves are bad seems unlikely.
Thanks and God bless, Sensei
Race Director
Joined: Nov 2002
Posts: 12,142
Likes: 54
From: Taylor Michigan
to check your needle and seat, remove the carb and then turn it upside down after you relieved the fuel.....blow into the fuel inlet....if you can then the float has not sealed the needle and seat....best case is if you cannot.....this eliminates most of the carb issues unless you missed some rebuilding item
mechanical pumps produce a average 4-6 lbs.
mechanical pumps produce a average 4-6 lbs.
Le Mans Master
Joined: Jun 2004
Posts: 6,231
Likes: 65
From: Seattle WA
St. Jude Donor '14
I can't think of any way the pump could start producing more pressure; it's a simple diaphram pump driven by the cam eccentric.
I agree the issue is most likely in the needle/seat - wouldn't be the first time I've seen a QJet rebuild kit with QA issues
I agree the issue is most likely in the needle/seat - wouldn't be the first time I've seen a QJet rebuild kit with QA issues
Le Mans Master
Joined: Nov 2008
Posts: 5,691
Likes: 12
From: columbus oh
your float pin has an arched top that sticks above the fuel bowl and wedges against the carb top to hold everything in place
check to see if the arch is high enough to avoid this problem....if too loose, it will create the issue you describe....good luck
check to see if the arch is high enough to avoid this problem....if too loose, it will create the issue you describe....good luck
Intermediate
Joined: Dec 2009
Posts: 32
Likes: 1
From: Snohomish Washington
Get a new float. Its hard to tell if the old one is defective. Its cheap and easily replaced. A heavy float could be causing your flooding issues. The plastic ones are notorious for this problem, they soak up a little fuel and get heavy.
Good luck.
Good luck.
Terrorizing Orange Cones
Joined: Oct 2007
Posts: 2,572
Likes: 17
From: Northern CO
I agree that a mech fuel pump would not increase output pressure, without touching it, per se.
I think the guys have offered other things to check that make more sense. Let us know what you discover and good luck.
I think the guys have offered other things to check that make more sense. Let us know what you discover and good luck.
Last edited by Dustup7T2; Jan 20, 2012 at 07:10 PM. Reason: correct text
Race Director
Joined: Oct 2002
Posts: 12,065
Likes: 2
From: Smalltownville Michigan
Cruise-In 5, 6 & 10 Veteran
St. Jude Donor '09
the pump doesn't produce pressure, but it produces flow. it's a constant volume pump. the likelihood of it increasing flow is really unlikely.
Drifting
Joined: Apr 2007
Posts: 1,970
Likes: 45
From: Cameron Park CA
The problem has gotta be either the needle/seat of the float.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Thread Starter
Melting Slicks
Joined: Mar 2006
Posts: 2,465
Likes: 0
From: Orange Park Fl
Thanks for the input. I did not think there was any way the pump would just increase output on it's own (although I know you can increase mech pump output preasure by pressurizing the weep hole, it's done to overcome boost in forced induction).
I was already planning to put another new needle/ seat in and replace the float unless someone knew something I didn't.
God bless, Sensei
I was already planning to put another new needle/ seat in and replace the float unless someone knew something I didn't.
God bless, Sensei