Quadrajet Problem Solving > Dialing in your rebuilt Quadrajet carburetor

77 carb with pre-75 rods

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Andyman:
Yes, the M4M designation I got off the internet, but my Haynes manual says its a M4V and it does have a forward entry fuel inlet. I don't have the manual yet. It does not backfire unless I try to accelerate, which I think indicates that its not the ignition system, and since I drove the truck 80 miles home without it misfiring, it's unlikely that the cam suddenly went bad after I did the carb work. Also, all of the wires test good with a timing light. I'm going to try the .045 rods again and see if that makes it drivable. It's pretty confusing when ALL the information available says that the rods changed dramatically in size in 1975 and there isn't any information as to why, or the possibility that some carbs didn't change over until later years. The problem is that if I need another size rod it takes a week to get one over the internet or I have to take a 1/2 day and drive to south Denver, but I don't even know what rods I might need to order yet. Thanks for all the help so far... but if there are rod sizes in the book could anybody please post what they are?

429bbf:
andy im not trying to send you in the wrong direction. and i hope its your carb. my problem was the car(1981 corvette 19,000 miles)electronic carb ran perfect as long as you didnt smash it to the floor and activate the 4 barrel. you could drive it 200 miles ran great. but when you laided it down and really got after it you could hear it backfire through the carb. so i talked to the man and ordered a complete rebuild kit . took the carb apart it was spotless even the idle tubes were clean. i put the kit in anyway because the carbs been on for 30 years. i wasted a lot of time because i didnt check everything out in the first place and i blamed the carb.ended up being a flat lobe on the intake. fwiw

Ethan1:

--- Quote from: Andyman on August 19, 2013, 07:12:47 AM ---Yes, the M4M designation I got off the internet, but my Haynes manual says its a M4V and it does have a forward entry fuel inlet. I don't have the manual yet. It does not backfire unless I try to accelerate, which I think indicates that its not the ignition system, and since I drove the truck 80 miles home without it misfiring, it's unlikely that the cam suddenly went bad after I did the carb work. Also, all of the wires test good with a timing light. I'm going to try the .045 rods again and see if that makes it drivable. It's pretty confusing when ALL the information available says that the rods changed dramatically in size in 1975 and there isn't any information as to why, or the possibility that some carbs didn't change over until later years. The problem is that if I need another size rod it takes a week to get one over the internet or I have to take a 1/2 day and drive to south Denver, but I don't even know what rods I might need to order yet. Thanks for all the help so far... but if there are rod sizes in the book could anybody please post what they are?

--- End quote ---

 Just to clarify, the carb in question is a 4MV Qjet. This comes from a well-respected manual I have. :D

Andyman:
SUCCESS! Next I put the stock .031 rods back in with .068 jets (.002 smaller than what was there already) and it ran like crap. It would not accelerate without backfiring and had no power. I changed all the spark plugs, and it ran a little better but not much. Today I picked up some new wires that I ordered yesterday and now its running awesome! Turns out that the spark plug wires were fine at idle, but apparently just would not transmit enough juice under strain. I can now go to work and test out how strong the hydraulics are with a load in the bed. It's an aftermarket dump bed that is bolted down with blocks of wood to the frame, which when down did not allow the stock gas tank to be filled. In the process of troubleshooting the engine, gasoline kept running out of the stock tank, which I found out was because a valve failed that was supposed to divert the return fuel back to the secondary tank. After removing the valve and rerouting the return direct back to the tank in use, I pumped the secondary tank full with gasoline from the other tank. I don't know how much gasoline is in the stock tank, but I'm expecting quite a bit more than the 30 gallons already salvaged. I can now relax knowing the truck isn't going to kill my budget!

Andyman:
Thanks everybody and I'm looking forward to reading the book when it comes. From what I've heard the only way to know what the stock rods and jets are, is to obtain a full GM shop manual for a C-30. Is this true? Anybody got one?

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