Quadrjet ? Need for vent valve
Thread Starter
Instructor
Joined: Jun 2004
Posts: 162
Likes: 1
From: Johnsburg IL
Quadrjet ? Need for vent valve
I recently got a great deal on a remaned quadrajet but concerned with the idle vent being removed and blocked off (normally attaches to accel pump linkage). I know the carb will have to be dialed in for my application but wondered if the missing idle vent valve creates any challenges.
Your responses appreciated.
Your responses appreciated.
Tech Contributor
Joined: Aug 1999
Posts: 14,382
Likes: 6,401
From: At my Bar drinking and wrenching in Lafayette Colorado
No problem with the vent being capped - the bowl vents through the vent tube anyway. The problem with that reman'ed carb may be as follows:
- It probably has a brass float. You should change it out with a NitroFill float (part number 2-440) and correctly set the float level to .375"
- The power piston has likely had its height set tang cut off, resulting in the piston being too low (lean). You may need to replace the power piston.
- The jet/rod combo is likely set to some generic spec and not to the correct spec for the carb number. Check and correct the jet/rod sizing.
- The secondary airvalve windup is likely too tight. Set it to 3/4 turn.
- The idle air bleed holes in the float bowl have likely been plugged with lead plugs. You need to knock the lead plugs out to get the carb to idle correctly.
Thread Starter
Instructor
Joined: Jun 2004
Posts: 162
Likes: 1
From: Johnsburg IL
Lars,
As always, you are the best resource for carb questions. I wanted to send you a pm but don't want to over stay my welcome!
By the way, do you have a good link suggestion with clear diagrams? All I have is what is left over from an old rebuild kit and my searches have not produced anything better.
The carb cost only $135 and is a 7041200 with new bushings. I have not confirmed the rod / jet size yet but was told they were original and should be a good starting point for my 383. The engine has an idle vacuum of 12 LBS.
As always, you expert advice is much appreciated.
As always, you are the best resource for carb questions. I wanted to send you a pm but don't want to over stay my welcome!
By the way, do you have a good link suggestion with clear diagrams? All I have is what is left over from an old rebuild kit and my searches have not produced anything better.
The carb cost only $135 and is a 7041200 with new bushings. I have not confirmed the rod / jet size yet but was told they were original and should be a good starting point for my 383. The engine has an idle vacuum of 12 LBS.
As always, you expert advice is much appreciated.
Tech Contributor
Joined: Aug 1999
Posts: 14,382
Likes: 6,401
From: At my Bar drinking and wrenching in Lafayette Colorado
If the carb is a 7041200 and it has a plug in the airhorn at the idle vent valve location, then the airhorn is not a 1971 airhorn - the carb has been pieced together from multiple carbs. The 1971 airhorns had the vent area cast closed, so there would be no need for a plug. Sounds like you may have a 1969 airhorn on a '71 carb. Better check that thing out well - it could be a real bag of worms.
Lars
Lars
Tech Contributor
Joined: Aug 1999
Posts: 14,382
Likes: 6,401
From: At my Bar drinking and wrenching in Lafayette Colorado
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Drifting
Joined: May 2006
Posts: 1,425
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From: Seattle Wash.
No problem with the vent being capped - the bowl vents through the vent tube anyway. The problem with that reman'ed carb may be as follows:
- It probably has a brass float. You should change it out with a NitroFill float (part number 2-440) and correctly set the float level to .375"
- The power piston has likely had its height set tang cut off, resulting in the piston being too low (lean). You may need to replace the power piston.
- The jet/rod combo is likely set to some generic spec and not to the correct spec for the carb number. Check and correct the jet/rod sizing.
- The secondary airvalve windup is likely too tight. Set it to 3/4 turn.
- The idle air bleed holes in the float bowl have likely been plugged with lead plugs. You need to knock the lead plugs out to get the carb to idle correctly.
I went to a TFB session in October and my "Rebuilt" Q-jet I purchased from a local rebuilder had ALL of the above problems present on it in addition to a couple of others not listed. Lars corrected and/or repaired the Q-Jet properly and it works like a dream. Beware of the generic rebuilds.
Okay, I'm going to avoid the obvious temtation presented by this statement! God bless, Sensei
Thread Starter
Instructor
Joined: Jun 2004
Posts: 162
Likes: 1
From: Johnsburg IL
Lars,
Appreciate the diagram. I will be taking this one back and have lined up a very good carb from another source.
The carb I found has the correct primary, secondary rods and jets for my engine plus the numbers match! Downside is the price is more than double.
Thanks for the help as always
Appreciate the diagram. I will be taking this one back and have lined up a very good carb from another source.
The carb I found has the correct primary, secondary rods and jets for my engine plus the numbers match! Downside is the price is more than double.
Thanks for the help as always
