What I learned about QJ's, after many hours, is that although they appear as if one carb is on a multitude of engines, from small v6's to mega 500 ci caddy v8's, it is the factory installed fuel restrictions, differing size air bleeds and idle by passes that make each one unique.

With that in mind, I searched for a QJ off a 301. I found one on ebay for less than I could of pulled one from the j/y. To my surprise I found it to be an 800 cfm QJ. (You can tell the difference by a bump in the venturi of the primaries. The 750 cfm QJ's don't have it).

I was very happy to find that the oem mixture screw covers had not been removed. It had never been rebuilt! That meant no parts had been interchanged in a mass rebuild. The carb was as GM intended it to be.

With the jets and primary metering rods, the conventional thinking is to have them about .030" apart. Like .070 jets with .040 m.rods. This was set, however, at .072 jets and .052 rods. When I stepped on it it bogged out. Finally I changed to .072 jets and .044 rods. Bingo. It was a love story. Idle smoothed out and made me smile. The acceleration just made me crack up.

I also adjusted the secondary butterflies to open all the way. I also ground off the air flap stop, allowing them to open 90*.

It is very fun to drive. Now I just want to buy the 1/4" thick base gasket that isolates the primaries on my Offy dual plane, and the 90* fuel inlet fitting so the fuel line clears the v.cover.

 

They sound a lot like a Weber. With a few what seem to be minor parts swaps you can pretty much dial in whatever you need. Sounds like you hit it out of the park on the first try!

Jim

 

I certainly didn't hit it the first time. This is the third QJ I've had. The first I ruined doing the rebuild, trying to drill out an oem plug. The second I ruined when I got a little too wild opening the factory fuel restrictions and air bleeds with a drill.

This one I left all the air bleeds and restrictions oem (that's why I got one off a 301. Equivalent size.) Still, I had to open the top about 10 times as i sorted through jets and springs, and m.rods.

My favorite part was when I went to the auto parts in the middle of dialing it in. It was running lean and when I pulled into a space beside a while sedan with a fat woman inside, I turned the key and the engine ran on. When my engine finally died, I heard the fat woman's doors lock.

 

Third time's a charm, huh?
Well, after all your attempts, you deserve to finally have one that's running right! That's crazy that GM would put, *stock*, an 800cfm 4bbl onto a 301ci engine. Heh, mathematically, that engine would have to rev up to 9200 RPMs to use the whole thing.

Very cool, I'm glad you've had success. I know I still need to find the *perfect* carb for mine. Maybe I need to search out the same one.

(What happened with the Autolite in getting the fuel to stop spraying out?)

 

Hello, AB--

I thought it crazy too with the 800 cfm, and stopped the project for quite a while. But then the 4100 went south, and so I put together the QJ with parts from the other, which someone ruined by getting a bit (pun) too wild with drilling air bleeds, etc. GM limited the s. air flaps to about 1/4 opening, and they cross drilled the s. nozzles. So that cut way down on the flow.

W/o the idle by pass air found on my other QJ (remember the rivets?), this will idle down to 550 rpm. It is very smooth. I think I paid $25 on ebay, with $15 shipping. I couldn't have pulled on from the j/y that cheaply. I highly recommend this model QJ. I give some tips over on FS.

I still can't find the 4100 needles. Only Mike's has them, and they don't have the opening at the bottom of the seat like I want, so that carb is on hold. I'm trying to crank out another book, so can't 'play' in the garage for a while.

k

 

"I thought it crazy too with the 800 cfm..." JMO, that is because of the miss-perception that just because the carb in it's total capacity is big that an engine has to handle that capacity. 4vs run primarily on the 2v side...just like a 2v carb and the total capacity is rarely if ever used.

 

Harte3--

The restrictions placed in the fuel passages and the size of the air bleeds drilled by GM determine the flow of any QJ. So they could take an 800 and 'dial it down'. I'm just surprised they would start with an 800 rather than a 750. Maybe to stay in the primary side longer?

I know that the 301's cross drilled secondary nozzles are peculiar to the 301, so they must reduce flow somehow.

 

I've always toyed with the idea of putting a qj or some sort if spread bore carb on mine..just like the thought of mpgs when needed and hoss when I need it haha. But then again..ask these 3 on ANY decision I've made and theyll be sure to tell you its like pulling teeth for me

 

I think the core QJ is quite versatile and could be used on a wide range of engines and I have always thought that one would best start with a model from a small block engine for the reasons you have stated...makes the dialing in much easier.

 

I have a very slight lean hesitation off idle, and, according to the tip in method, where you cup your hands over the primary air intake side to reduce air flow, I am idling slightly lean. I tried to adjust the mix to compensate, but could not. C. Ruggles recommends changing the idle tubes to ones with a few thousandths larger restriction, and opening the idle channel restriction 3/1000's. But that would mean buying a machinist's bit index, and right now I just want to drive it. Maybe I'll jump into that later, depending on what I find out with the mpg. I was also told by C.R. that I should change the s.nozzles. The 301 QJ's secondary nozzles are cross drilled, and once the air flaps are opened by oem setting, their dispersal is not adequate.

 

Either way though, it sounds like it's really close "out of the box". Very cool.
Although, they must've caught wind of that because there's no cheap ones on Ebay.

 

AB, you want me to grab a QJ for you to play with? They're everywhere on cl down here. Probably ten bucks, maybe even free if you're not in a hurry.

 

I have three in garage. I bought them all for $25 on CL. However, although there are many of them around, it's difficult to find one that hasn't been spliced by a mass rebuilder.

 

Hey Baron,
That'd actually be really cool. I see them on CL here from time to time, but they're not very common. About 1 a month or so. I'm getting a wideband O2 sensor soon of my own, so it'd really help with something like that. As F-250 said, one from a equally sized engine would be the best bet. I just don't think I'm up to the task of trying to re-tune for a bigger engine as he did.

Still need to give that Eddy a try, but currently my brother and I rebuilt it (on his dollar) and he has it on his motorboat, so I know it's up and running! The season's over, so he won't be using it for a while...

 

Yeah, don't try to got from larger to smaller on the QJ. All mods are based on enlarging the restrictions, not the other way around. It was simply way beyond my skill level once you throw in idle by-pass, air bleeds.

One other thing to be aware of, is to try to find one w/o a mass rebuilder sticker on the carb. I've been told they often interchange the three components, when GM designs all three to work together. I think that's another reason the QJ got a bad name; you interchange one section with that of a diff. QJ, and turning becomes virtually impossible, unless, or course you are a carb guru.

Make sure you get a post ethenol kit. Oh, and atop the power piston is a little collar that doesn't come in the the kits. Quadrajet dot com has them cheap. Get the four spring 'kit' for the p.piston while there. Post 1975 QJ's did away with the leaking plugs below the bowls: that means a 1705(5) or younger. The sixth digit refers to Federal use or California smog carb...lean.

Oh, m.rods are different lengths, pre and post 1975. The Edelbrock rods on Summit (cheapest) are the shorter, and fit post '75 carbs.

You can tell the 800 cfm from the 750 by the lumps in the primary bores of the larger cfm carb.

A great source of info is the forum on the cliff ruggles site. Good luck.

Oh, get the oem throttle bracket from a j/y. I found it a good place to begin with a linkage bracket.

Also, I have amassed a virtual QJ museum in my garage. Be sure to ask about spare parts before you buy anything. I'd be glad to send you anything I have. k