454 Quadrajet Question

[shaferg]

Hello all, I just recently completed building this bbc and putting it back in my 93 nissan  300zx.       Heres the build-------->>>>   .http://forums.nicoclub.com/454-powered-300zx-t485062.html
The issues I am having are: 1.Engine will not run by itself on the fast idle cam without a sligt throttle blip which most times brings it off the fast idle and on to the regular cam and I have to hold the throttle until warm. It will also idle very low sometimes(500-600 )after warmed up and at a light in gear. Sometimes will idle at 900-1000 as set.
    2. Engine seems to flatten out power wise at about 3500 rpms and when floored(wot) will sometimes fall flat on its face, surge then even out.
I have read Cliff's book 4 times to try and understand Quadrajet function but the info is sort of overwhelming.

Engine specs: 454 bored .060 over
                     Pass heads
                     Flat top pistons
                     cam 513 lift, 230 duration @.050
                     200-4r transmission
                     4.08 rear
                     

[omaha]

   Ok, What is the carb number. what  are the carb specs. I know that certain QJ's would be a bad choice for that engine in their  stock configuration, how ever, the majority of them can be made to work if the casting is useable. I wil assume that you will need a fair amount of fuel at idle and maybe bypass air.  All hinges on what carb number you have on it right now.

[shaferg]

There are multiple numbers on the carb, but the air horn number is 17083224. I bought the carb remanufactured from National Carb in jacksonville florida. Claimed flow is 795cfm

[Ethan1]

 That is a remanufactured carburetor. A lot people have problems with them right out of the box.

[shaferg]

Thanks for letting me know its a remanufactured carb.

There are multiple numbers on the carb, but the air horn number is 17083224. I bought the carb remanufactured from National Carb in jacksonville florida. Claimed flow is 795cfm

[Ethan1]

Thanks for letting me know its a remanufactured carb.

 Oops, my bad. Thought it read replacement, not remanufactured. Totally different.

[omaha]

the carb 17083224 is a chevy carb used mostly on chevy/GMC pickups. Nothing wrong with them basically however they were known for being set up very lean with large air bleeds (I think main single air bleed). Also equipped with a rear type pull-off. I don't know of the remanufacturer where you bought it BUT just being remanufactured does not mean that all is right.  try to take some measurement of the idle circuit/main circuit specs. Things like air bleeds and various idle orifice dimensions can make a big difference especially on  that carb. In the end, you may need to make some modifications. The QJ is the best 4 brl in the world but must be tailored to the specific application that you are using it on. Yes some applications will overlap on stock type builds. This is where the "recipe's" come into play (from the book).
     I like your build project.....sweet!!!

[shaferg]

Im not sure how to measure idle circuit main circuit specs, but Im sure something is wrong because the engine will turn over and over and not start after a short trip. This has gotten worse over the past 2 weeks. I believe fuel is draining from the bowls somehow or fuel pump is draining back. Is this common? It looks like I need to become a Quadrajet expert but I have to dump some memory as my brain cannot hold info on every moving part of a combustion engine and drivetrain. Thanks for the help.

[Ethan1]

 If your turning the motor over and over and nothing happens, and your loosing fuel. Sounds like maybe your leaking fuel out of the bottom well plugs.

[shaferg]

Leaking plugs are one possibility, Im going to swap my fuel pump from a stocker to a holley to rule out the fuel pump. My gut tells me the ethanol laiden fuel is not making things any better for the rubber components. Could fuel be draining back or leaking out the plugs and what would be a good way to tell? Im still trying to address the drop off in power @ 3500rpms if anyone would like to chime in with theories.

[omaha]

Well, yes the gasoline these days does wreak havoc with the rubber in the old carbs. That is why it is wise to use the parts that Cliff sells in his kits. They are made of "alchohol resistant" rubber. To test for well leaks you need to use air pressure and some soapy water. Hey, this advice comes straight from Cliff's book. As far as the power loss at 3500 I will take a guess that the fuel bowl might be starting to empty. You may need to drill out the needle's seat or just get a larger needle /seat assembly. Also make sure you have enough fuel supply to the fuel inlet/3/8 fuel line, good pump etc cause the QJ has only one inlet you know. all this stuff is in the book and I would not let the qj intimidate you. It actually is not too bad to work on. Maybe get a spare at a swap meet to take apart just to familiarize yourself with it. Also Cliffs book is most important to read thoroughly. Yes it might be mighty tempting to go with that other brand carb BUT once you get the QJ dialed in, it is way better on the street that anything you will find. AFB's are just cylinder washing devices as far as im concerened. Holleys will work for a while but also do not have the atomization qualities of the QJ. 

[shaferg]

Im sticking with the QJ for now. If one man can build one to work then I can also. I emailed Cliff to ask him what kit and/or what size jets and metering rods to start with. As far as the recipies in the "book" they are a bit confusing. Im better at following directions then trial and error. Hopefully Cliff can steer me in the direction of a good starting point for my setup.