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Anyone have much experience with Quadrajet's?


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18 replies to this topic

#1 GeneralDisorder

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Posted 11 January 2010 - 02:27 PM

I'm working on this '69 GMC Custom Camper - I'm buying it from a friend and fellow Subaruphile but we need to get it running first so it can make the trip to my place from it's home some 40 miles away.

Anyway - it's a 350 SB with a Q-jet - apparently the engine is from a '77 GMC van, and the carb is from yet something else - the date code says it was made in '80 :rolleyes:. That's really all the info we have as it was bought this way with some plug wires crossed and a lot of loose bolts from some idiot that didn't know which end of the ratchet was up.

We have it running, but it's rich. Black smoke rich. My friend rebuilt the carb and he's got experience with older Q-jets and with Holley's so I have no reason to doubt his rebuild. He's clueless when it comes to the jetting sizes and he has no internet access so I'm starting with what I know - and that's the members of this board :)

I have searched the internet and all I can seem to find is discussion of what jetting people are using on performance built 350's - nothing about what a stock 350 should have.... ballpark. The engine is used - runs good and apparently ran good when they pulled it from the van - we don't have any idea if the carb was on it at that time or not though and we can't go back to the last owner for info as it was bought several years ago and he's lost the contact info.

Anyone have a clue as to what I should see (approximate) for a stock 350 SB main jets, metering rods, etc?

If nobody knows, where should I ask? Anyone know of some friendly forums catering to general SB Chev stuff? I'm sure I'll have other questions about the truck anyway as it's going to need some other repairs once it gets here - not to mention a front disc brake conversion :rolleyes:.

GD

#2 lostinthe202

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Posted 11 January 2010 - 03:17 PM

I've got a FSM for a chevy c10's from the 80's at home. I'll see if there is any info in it that is pertinent when I get home.

Will-

#3 Txakura

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Posted 24 January 2010 - 04:30 AM

I'm working on this '69 GMC Custom Camper

Anyway - it's a 350 SB with a Q-jet - apparently the engine is from a '77 GMC
van, and the carb is from yet something else - the date code says it was made in '80

We have it running, but it's rich. Black smoke rich.

stock 350 should have.... ballpark. The engine is used - runs good and apparently ran good when they pulled it from the van -

Anyone have a clue as to what I should see (approximate) for a stock 350 SB main jets, metering rods, etc?

GD


this is at idle it's running rich?
I'm assuming that the choke is clean and functioning after the rebuild and the timing and idle are at the spec

my Peterson's 'Big Book of Auto Repair Complete Specs on American Cars 1967-1983' says that there are two factory sealed plugs in the throttle plate to prevent tampering with the idle mixture screws. Is that the case?

Are there any emissions on this?

if you can get to the idle mixture screws it says backing them out is richer. there is a procedure, but I'll wait to hear back. if you can get to them, and get them out, shoot some carb cleaner through the idle passges

I've got some specs for the Rochester M4MC, M4MCA, M4MEA and general stuff for the 4bbl (4MV).

I got tables and tables, but no metering rod lengths. The only jet sizes shown are for 1969-70 carbs, (.076 and .078 (both primary diameters depending on engine)) probably not useful info...

see if you can find any numbers on it, I might be able to run some stuff down, we have a lot of old tech still on the road here

#4 T'subaru

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Posted 24 January 2010 - 08:24 AM

I've rebuilt a few over the years. I'd recommend looking at replacing it with a new carter....should be very low 200.00 at most parts stores...would not buy reb exch. We used to refer to them as "quadratoilet" :) Check for surplus at ase supply ( in portland ) asesupply.com i think.
Good luck, Mark

#5 Quidam

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Posted 24 January 2010 - 08:27 AM

From notes: 350ci '78 GMC. 64 primary jets, 39 primary rods. DP secondary rods w/.006 tip.

350 ci. Olds, 77 jets, 52 rods, DR rods secondary.

Of course it varies with altitude and the particular engine, but you should be in the ballpark.

The metering rods act as the power valve on these.

I've got more, but i'll have to look them up.

#6 Quidam

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Posted 24 January 2010 - 08:30 AM

" We used to refer to them as "quadratoilet" :)"

He should rip that thing off there and use an adaptor plate and put a Holley on it:) jk

#7 T'subaru

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Posted 24 January 2010 - 08:32 AM

" We used to refer to them as "quadratoilet" :)"

He should rip that thing off there and use an adaptor plate and put a Holley on it:) jk


Yep, and I think Holley fixed their back fire and its toast thing years ago:)

#8 Quidam

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Posted 24 January 2010 - 10:47 AM

The main jet range is about 47 to 81, and Quadrojet, Dualjet, and 1 barrel jets are the same.

The Holley/Quadrojet thing is like the Weber/Hitachi thing. Holley and Weber are by design easier to work on, service, rejet, set float level, center pivot float, mechanical linkage if you want, etc.

But a Quadrojet is a good carb, if you know what you're doing. Spread bore like the Hitachi, but it doesn't have removable/adjustable air bleeds and such.

He could change it out for SPFI, that would be best:)

Edited by Quidam, 24 January 2010 - 10:52 AM.


#9 GeneralDisorder

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Posted 25 January 2010 - 01:48 AM

I got it fixed. It was a couple things actually.

Turns out - my friend that had it apart *may* not have been the first. The previous owners, upon swapping the engine, could not get it to run correctly. They proceeded to tear down the carb (I'm guessing) and tried their hand at repairing it. In the process they bent the crap out of the rod holders on the top of the vacuum piston for the primaries and bent one side of the secondary rod hanger as well. Probably trying to jam it together without much care. The rods were being held high by about 1/4". I got a parts carb at the junk yard - found almost an identical model from a Dodge with a 360 in it and used the piston and secondary hanger from it.

Got that fixed but it still didn't run right.

Finally pulled off the timing chain cover and layed (my) eyes on the timing marks - they were fine but the balancer has it's timing mark posistioned such that it's supposed to be timed to a scale on the CENTER of the timing chain cover - not the one that was ALSO bolted to the side of the cover. So in the end it was timed somewhere around 22 degress ATDC, when it should have been 6 degrees BTDC. I created a new mark on the balancer as the old mark and scale are entirely obscured by the water pump :confused:. Weird.....

Anyway - after my carb rebuild and new ignition timing mark for the side-mounted scale it's running like a demon. I was finally able to bring the truck home 40 miles.

The carb should be good for a while. It's got a sticker on it claiming it was "Rebuilt by Holley" - seems odd they would rebuild a competing product but whatever. It actually seems a simple enough carb - runs real good though I think I'll replace the choke with an electric. I like the design of it and it's not without performance potential. I particularly like the progressive secondaries - the air valve can be adjusted for speed of opening - that's a huge advantage over vacuum secondaries but retains some of their driveability charataristics if that's what you desire. Very interesting design. I may play with it more.

I can see how people would argue between Holly/Q-Jet, but the Q-Jet has some serious advantages over the Hitachi's. And people do use them for some serious performance applications. The adjustable secondary air valve pretty much eliminates the secondary lag problem of the Hitachi design. The air valve system can be adjusted/modified to open rapidly and the Q-jet has the enrichment system to handle that potential.

As for fuel injection - probably not on this truck. I have no real desire to mess with the SPI of the 80's GM products. Not that it's a bad system - I just have too many other things to mess with. This truck is just dandy with a carb - it's a utility vehicle and I'm perfectly at home with the carb it has on it. Someday I may consider building a 383 for it, and I don't know that SPI would scale to something built for 300 HP. I know I could make the Q-Jet do it though.

GD

Edited by GeneralDisorder, 25 January 2010 - 01:58 AM.


#10 2.5_IMP

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Posted 25 January 2010 - 11:37 AM

The carb should be good for a while. It's got a sticker on it claiming it was "Rebuilt by Holley" - seems odd they would rebuild a competing product but whatever. GD


I just sold a Toyota 22R Carb that had a "Remanufactured by Holley" sticker on it. I saw an article in Hot Rod a while ago about Holley rebuilding carbs in-house, but I never thought they would touch an asian Aisan!

#11 Quidam

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Posted 25 January 2010 - 12:15 PM

Hi,

Yea, last two reman Hitachis I snagged of ebay were Holley. They are CarbsRUs, custom shop, etc.

Doug

#12 GeneralDisorder

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Posted 25 January 2010 - 01:06 PM

I guess that makes savy business sense - the market for carbs is shrinking every year and if they can't sell you a new Holley then at least they can make some coin off you by useing their expertise to rebuild your existing carb. And maybe you'll come back to them when you do want a new performance carb.

Makes sense since most of the carbs out there are now orphans - the Q-Jet is a good example. No longer produced - though at least in it's case they made millions so there's plenty of parts around.

GD

#13 Quidam

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Posted 25 January 2010 - 02:09 PM

Hey GD,

Yea, I've still got 4 of them. ebay one of these days. If I remember right, Edelbrock, or some company, started making new ones.

Doug

#14 Quidam

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Posted 25 January 2010 - 04:00 PM

http://www.carbureti...m/Rochester.asp

According to this, they have stopped making new, but it was Weber.

#15 GeneralDisorder

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Posted 25 January 2010 - 04:18 PM

http://www.carbureti...m/Rochester.asp

According to this, they have stopped making new, but it was Weber.


Yeah - I read that about a week ago when I was looking at options. Guess there wasn't enough demand. People find them overly complex I guess.

GD

#16 GeneralDisorder

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Posted 25 January 2010 - 09:03 PM

Discovered that the Q-Jet has the leaking welch plugs - it's getting the JB weld treatment as we speak. Hopefully that cures the rich idle and fuel leaking out the throttle shafts.

Time to change the oil..... again :rolleyes:

GD

#17 hatchsub

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Posted 27 January 2010 - 09:01 AM

thought this might help ya GD. I get HPP in the mail and they recently did a article fixing most of the problem areas of the Qjet. I found this one and the other one on the Muscle car site.

http://www.highperfo...ning/index.html

http://www.powerbloc...35fa32c&page=18

Not sure it is of any use to you but i figured they were both good sources.

#18 capn_r

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Posted 27 January 2010 - 12:36 PM

Something I ran into a few times forever ago with QJ's was the nitrophyl (sp?) float getting a little heavy (starting to saturate) thus letting the inlet needle valve not seat correctly and causing the carb to run fat. If I remember correctly you sat the float on a flat surface tipped back against the end where the needle attaches and if it would stay in that position it was probably okay. If it tipped forward it was probably getting heavy.

#19 GeneralDisorder

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Posted 30 January 2010 - 01:35 AM

Thanks for the links Steve - I'll check those out.

I beleive the float is part of the problem. I have a brand new float and needle/seat comming (as well as an electric choke for it :banana:).

What I did find though - after I sorted out most of it's problems, was the fuel pressure from the mechanical fuel pump I put in is just WAY too high (or the float is weak). The pump was new - I figured maybe it was bad (over 10 psi on my cheap guage) so I replaced it. Same problem - I thought there was a slight possibility of the fuel pump having sucked in some rust and corrosion from the tank so I replaced it a second time. Same problem. Three pumps and the pressure is still high enough to blow the needle off the seat at idle or after shutdown and fuel would overflow the bowl and drip out the primary throttle shaft bore. This third pump was installed with brand new clean fuel line and a brand new paper element filter (clear - so I can check for blockage) before it from the supply line. After the third pump showed the same symptoms I installed a fuel pressure regulator set to 4 psi and the problem has not returned.

I guess I'll install the new float and needle/seat when I get them as well as the choke. But I'm leaving the pressure regulator in place. Can't hurt and definitely seems to curb all the nasty symptoms I was having.

So - problem solved for now.

GD




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