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Old 07-04-2011, 06:32 PM
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Restoring and tuning a quadrajet

I've got a quadrajet #1705 8212 from a 1978 heavy duty 454. I've got it working OK now (had a big flooding problem a few weeks ago) but it still leaves me with more to be desired.

Heres some issues i'd like to check and work on:

1. I feel the engine is running rich (the exhaust smells like it is but there is no visible smoke)

2. It has the typical quadrajet problem where the fuel leaks out of the bowl when its shut off for a few hours and takes a bit of cranking to get it started again. Once it starts it runs great and all but I just know its not right.

3. I removed the choke. I lost a couple of the rods that connect the coil on the intake to the choke parts on the carb, so I removed some of the choke parts (like the butterfly on top) Its not proving to be a problem, but i'd like to install an electric choke kit before winter.

4. Id like to check all common wear points, throttle shaft, body to air horn warpage, etc and get this thing back up to snuff where needed.

5. Id like to tune it. Metering rods, jets, etc. I'm sure its tuned for emissions rather than power or mileage but mileage is of highest concern for me at least for now. However, I dont want it to be a dog. It IS a 454 after all, and there is a reason for that. A 350 would probably have been fine for my needs, but I had alot of big block parts and a big block is what I wanted so that's what I've got. I dont need it for the acceleration power, I need it for the tow power. Getting the emissions crap tuned out of it and getting the primaries tuned for best mileage would be nice. I did notice on this carb that the power piston (i believe that's what its called) doesn't have adjustable spring tension on this carb like some qjets do. To tune it, I guess you change the springs under it. So maybe I need a better carb?

Also I noticed that currently, the primary jets are much larger than the metering rods. The metering rods will completely pass through the jets when they are removed from the carb. This means it cant come anywhere near close to shutting off the fuel. I know that you dont want it to be able to shut the fuel off, but it should be close right? Perhaps this is part of my rich running problem?

Anyways, that's what I'm asking here for, to get help in determining what to do.

Thanks in advance!

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Old 07-04-2011, 09:37 PM
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There are two good books that will give you an education in qjets. Cliff Ruggles is the book I chose. He also has a q jet forum at cliffs high performance dot com. He rebuilds q jets and will sell you parts, and he'll answer questions on the phone. Start with the book and read it several times, it'll answer most of your questions.
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Old 07-05-2011, 02:25 AM
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I'll see about getting that book.

One thing I noticed on this carb tonite is that even tho it IS a 75+ model carb (as indicated by the model number starting with a 170 instead of 70, and being removed from a 78 HD 454) it does NOT have the APT adjustment screw in front of the power piston. This really bugs me alot as I was really hoping to use that adjustment to my advantage. I suppose the only way to adjust the APT would be with one of four different springs that are available. Not much of a fine tuning adjustment that way.

I am thinking maybe I need a different/better carburetor to start with.
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Old 07-05-2011, 05:46 AM
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Quote:
Originally Posted by Torque454
I'll see about getting that book.

One thing I noticed on this carb tonite is that even tho it IS a 75+ model carb (as indicated by the model number starting with a 170 instead of 70, and being removed from a 78 HD 454) it does NOT have the APT adjustment screw in front of the power piston. This really bugs me alot as I was really hoping to use that adjustment to my advantage. I suppose the only way to adjust the APT would be with one of four different springs that are available. Not much of a fine tuning adjustment that way.

I am thinking maybe I need a different/better carburetor to start with.
Check the front of the throttle plate casting for a blocked off screw that is the bottom stop for the power piston. This can be used instead of the 'normal' APT adjustment to get the rods where you want them in relationship to the jets.

There's usually (depending on the carb, not all are the same) about a 30 number difference between the jet and rod. This can change depending on the air bleed arrangements, etc. but gives you an idea of just how much difference you may see between the jet and rod.
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Old 07-05-2011, 01:52 PM
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Quote:
Originally Posted by cobalt327
Check the front of the throttle plate casting for a blocked off screw that is the bottom stop for the power piston. This can be used instead of the 'normal' APT adjustment to get the rods where you want them in relationship to the jets.

There's usually (depending on the carb, not all are the same) about a 30 number difference between the jet and rod. This can change depending on the air bleed arrangements, etc. but gives you an idea of just how much difference you may see between the jet and rod.
D*mn you're good, cobalt. I totally missed that little adjustment screw in the base plate. Its not blocked off, but it is dirty. I never even looked in the base plate anyways, i was looking above the float bowl behind the power piston for a screw with an aluminum plug over it.

I'd never heard of it being in the base plate before.
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Old 07-05-2011, 08:05 PM
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Thanks for the vote of confidence. The baseplate mounted APT is easier to get to, IMO. I like to free it up real good and use teflon tape if needed on the threads to keep the screw threads tight. There's often carbon built up around the lifter arm, try to get all of that cleaned out so the lifter arm is free to move w/the adjustment screw. It's only staked in position so take care not to upset this while cleaning it.

Before removing the APT adjustment screw, get a baseline measurement for the APT "lifter arm" so you have something to go to if need be. The depth rod of a caliper works good for this.

Another adjustment that's not commonly recognised is the idle air bleed screw that is present on some carbs. It's located under a triangular piece of thin spring steel where the front vent is located, seen in the Ruggles book cover below:

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Old 07-05-2011, 08:25 PM
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I like the idea of the base plate mounted APT adjustment also. I have two identical carbs (17058212) and one of them I have right here beside me (disassembled). I do see the nasty carbon buildup that you're talking about and as soon as I saw it (when I looked at the APT earlier) I knew it would need to be cleaned. I dont think at this point that the adjuster would work at all with all the gunk in the area.

I'll be sure to get a base line setting before I mess with the APT screw. I'm not totally sure if it needs to be adjusted or not, but it cant hurt to change it a little at a time until it has a negative affect and then change it back a little I wouldn't think. This carb just seems to run too rich IMO.

Also, It looks like my carb does not have the idle air bleed screw adjustment.

Sure wish I had an A/F ratio monitor. That would help alot.

If I could get it to 14.7:1 at cruise and 11.7:1(?) on acceleration that would be awesome, but to get that good of a tuning I fear i'd probably have to have fuel injection.

Thanks for everything so far!!
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Old 07-05-2011, 08:28 PM
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BTW I'm really starting to like this carb - still wish I had EFI but this is pretty close.

I am thinking of trying to find parts for use with alcohol fuels to install in this carb since there is so much ethanol in our fuel. I'm pretty sure its causing me some problems with ALL my carb'ed engines.

I'm assuming the alcohol compatible components are compatible with gasoline still?? Surely they are...
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Old 07-05-2011, 08:35 PM
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Quote:
Originally Posted by Torque454
BTW I'm really starting to like this carb - still wish I had EFI but this is pretty close.

I am thinking of trying to find parts for use with alcohol fuels to install in this carb since there is so much ethanol in our fuel. I'm pretty sure its causing me some problems with ALL my carb'ed engines.

I'm assuming the alcohol compatible components are compatible with gasoline still?? Surely they are...
Yes, they are compatible by everything I've read and heard. The kits Ruggles sells are guaranteed to be alky fuel compatible, but truth be told, I've not had any problems w/any of the 'regular' kits like Walker, etc. that are sold by the major parts outlets. Very early on there were probs, but that seems to be a thing of the past, now that we've had alky in gasoline in many areas for a long time now.

A couple links, etc. that may be of some use:

Q-jet rebuild w/photos- HERE.

Q-jet Carb Adjustments- HERE.

Manual w/exploded view- HERE.

Gessler has most if not all of the small, hard to find parts.

Ruggles has quality parts and rebuild kits and services like primary bushing installation. He does correct restoration of Q-jets, too. Consider buying his book "How to Rebuild and Modify Rochester Quadrajet Carburetors". Another book is By Cliff Roe, called "Rochester Carburetors". Most say they'd probably get the Ruggles book first.

A thread here on Hotrodders that has some good info and photos- Rochester Quadrajet 4MV Carburetor: Removal, Disassembly, Rebuild (Rookie Level)

Last edited by cobalt327; 07-05-2011 at 08:48 PM.
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Old 07-05-2011, 08:46 PM
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Yeah its not very easy to get gas here without ethanol in it. Missouri state law REQUIRES all gas UNDER 91 octane to contain at least 10% ethanol. 91+ isn't required to have it, but alot of stations have ethanol in the 91 too. There is only one station that i know of for sure that does not have ethanol in the 91.

I try to get fuel there, but its rather inconvenient.

I am concerned about ethanol after having alot of carbed engine problems in the last year or two. Just this last couple of weeks I had two different carbed vehicles with severe flooding problems all within a week or so of each other. Then last summer I had one with that problem too. Its getting old and I feel that ethanol may very well have a part to do with it.
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