Quadra-Jet Question? Help Please!

[vexvader]

Running rich I think...

I have a 1970 C10 with a 350 small block and a 4 barrel Quadra-Jet. The engine and carb are from around a 1981 truck. It runs GREAT, tons of power, it does not burn any oil or smoke. I have not done a compression test on it and it has about 100k miles on it. I have played with the timing and tried a couple different settings.

Here is the problem:

1.) The exhaust smells very strong. A very strong CO2 smell. Kind of like a 2 stroke outboard boat motor. Whenever I drive it for 10 mins or more my clothes smell.

2.) There is a black stuff building up on the inside and the ends of the exhaust tips.

My experience tells me that the motor is running rich, so i tightened down the two screws on the front of the carb. They are all the way in (tight as they can go). They will not turn any more. I have never worked on a Quadra-Jet and not sure how to tune it or even if I am on the right track.

What should I do?



PS: Please keep all the "quadra-flood", "quadra-junk", "quadra-crap" comments to yourself. I would most definitely prefer to just go buy a new Holly or Edelbrock, but I don't have the funds right now. What I need is suggestions to fix my problem. Thanks!!!

[vexvader]

Here picture of the bolts that I think control the mixture and I have tighened down. The carb in this pic is a little newer then mine but I am pretty sure this is the same bolt.

[crm318]

Those are the idle mixture screws. They shouldnt have an effect on part throttle performance. Has this carb always acted like this? You might need to go leaner on the jets and needles.

[vexvader]

Originally Posted by crm318

Those are the idle mixture screws. They shouldnt have an effect on part throttle performance. Has this carb always acted like this? You might need to go leaner on the jets and needles.

Yeah, it has done it for the last 5 years that I have had it. It smells during idle and when driving around at half throttle.

Do you agree that it is running rich?

Thanks for the help!!!

[crm318]

Yeah, the symtoms point towards rich. You should also pull a few spark plugs to see if they are fouled. It sounds like a good time for a rebuild and possibly a float adjustment. If your not familiar with the inner-workings of a quadrajet, there are many books and websites that can assist you. A good operating quadrajet is hard to beat. I have a one and will never use another carb.

[capev86]

A good operating quadrajet is hard to beat. I have a one and will never use another carb.

AMEN!!!

if you rebuild it, get a rebuild kit from Cliff's High Performance. they carry every bit you could possibly need including bronze bushings for where the throttle shafts ride in the body. Edelbrock carries hi-po parts for q-jets also, but Cliff's has more stuff together in the kit rather than buying seperately. the best improvements over stock are the better float and especially the shortened accelerator pump that allows for quicker reaction time and less chance of fuel starvation at sudden throttle jabs.....not that i've ever had a problem. don't forget to file down the ends of the screws on the throttle blades. they are split once installed to keep them in and they come out hard and often break if you don't dress them first. i found this out the hard way. you want to be sure to use locktite when installing the screws so they don't back out and fall into the engine.

i am replacing the 2 barrel on my 72 burb (has a 307 that will eventually be replaced by a 406sbc) with a reman'd 85 q-jet. i bought an edelbrock performer intake (idle-5500rpm range) and also putting in a brand new 4 row radiator at the same time replace the 2 row unit. the intake is an older one but was never installed and looks beautiful in the original box. i will be reinstalling the petronix equipped original distributor and using the huge air cleaner box off my dad's 84 burb (need to get it blasted and powder coated). i was going to use the q-jet off his truck (had it on that 406) but i realized i am short on time with all the other projects needed to be done on the truck before she starts hauling the vintage family camper in a couple months (71 holiday trav'ler 23 footer that weighs 6,000 lbs loaded). i figure the q-jet will get me slightly better fuel mileage AND more performance than that rochester 2 barrel could ever hope to do.

[bruceman1968]

http://www.florida4x4.com/tech/quadrajet/index.php Here's a web page (not mine) with lots of q-jet links. sorry I don't know enough to help you................

[vexvader]

Originally Posted by bruceman1968

http://www.florida4x4.com/tech/quadrajet/index.php Here's a web page (not mine) with lots of q-jet links. sorry I don't know enough to help you................

That site rocks!!!

[zac]

Could be the power piston stuck in the up or rich position. Sometimes varnish forms in the piston bore and it sticks so that it can no longer respond to vacuum changes, so the primary metering rods can no longer do their job. You can see the top of the metering rod hangar if you look down the vent (that tube on top of the carb). You can put a very small screwdriver down there and push the piston down if it is stuck up. I

[vexvader]

Originally Posted by zac

Could be the power piston stuck in the up or rich position. Sometimes varnish forms in the piston bore and it sticks so that it can no longer respond to vacuum changes, so the primary metering rods can no longer do their job. You can see the top of the metering rod hangar if you look down the vent (that tube on top of the carb). You can put a very small screwdriver down there and push the piston down if it is stuck up. I

Thanks I will try it.

If I push it down will it stay. Should I spray some carb cleaner down there?

Vex

[50mercfan]

People make fun of Q-Jets because they're more complicated and they don't know how to work on them. If you've got your idle mixture screws turned all the way in, somethings wrong, it shouldn't idle that way. You are cutting off all the air and fuel at idle. When you are off idle they have no effect at all. If it's idling in this position you have to have a vacuum leak. Doe's the truck idle rough? hesitate under partial acceleration? I assume not since you said it runs good. Thats a mystery in itself.

As far as your rich running situation, two things jump to mind. Your float level is too high, or there is trash in your needle and seat. Both of these could be causing raw fuel to drip from the boosters at normal driving speeds.

Let the truck idle normally and look in the top of the carb. Look for drips of fuel falling from the boosters. (look all around those round things sticking out in the middle).

check your timming. make sure your good there. you could also switch to a hotter spark plug. you'll be suprized how many times a bad carb. turns out to be an ignition problem

[highperf4x4]

mercfan is right. If you have the idle jets all the way then it shouldn't idle at all. Might be time for a carb kit and good cleaning.

[zac]

If the truck is off, the power piston should pop back up freely as there is a spring under it. If it doesn't or seems kind of sticky, you may have found the problem. A little carb cleaner down there probably won't really hurt, but it shouldn't be considered a fix. It would still need a rebuild. When the truck is running at idle, the piston should be down all the way. At high vacuum, the piston keeps the fat part of the metering rods all the way down in the jets. They come up to expose the thinner tips of the rods as vacuum drops under acceleration to richen the mixture. My idea is that maybe they are stuck in this richer condition, although this may not really be a factor at true idle.

Check to see if you have Q-jet nozzle drip. At idle, no fuel should be dripping out of the nozzles in the primaries at all. But many times it does because the curb idle screw has been turned up because you have a bigger than stock cam. Also, large displacement engines will have this problem because they require relatively more air at idle. The Q-jet booster rings are so efficient that any air flow through them can cause the nozzles to drip, which can give you rough idle and a seemingly rich condition. This is why Rochester developed "idle bypass" for some carbs which will allow an engine to idle perfectly with the butterflies completely closed. It's why I use old Caddy carbs exclusively.

People have mentioned float level as well. Either way, sounds like you need a rebuild. Take your time. If you spend a little time reading up on how these things work, it makes alot more sense.

[DT1]

IMHO, the Quadrajet is probably the best carburetor ever made. They can be a bit intimidating to someone that has never seen the inside of them but they are very "Tunable."
One problem most of them share is the phenolic float. After a few years, they will actually start to soak up fuel causing the float to drop and cause a rich condition.

[vexvader]

Thanks guys for the help!! I will let you know what happens.

Vex

[71longbed-brew]

great thread .... i think my carb might need some attention

[Chevydude56]

Powerblock TV /Musclecar had an episode that included rebuilding Q-jets

http://www.powerblocktv.com/video/?ep_show=MC

[highperf4x4]

Originally Posted by Chevydude56

Powerblock TV /Musclecar had an episode that included rebuilding Q-jets

http://www.powerblocktv.com/video/?ep_show=MC

Thanks!

[vexvader]

Originally Posted by Chevydude56

Powerblock TV /Musclecar had an episode that included rebuilding Q-jets

http://www.powerblocktv.com/video/?ep_show=MC

I saw it. I am still a little unsure about diving in.

Vex

[highperf4x4]

Originally Posted by vexvader

I saw it. I am still a little unsure about diving in.

Vex

That means you will probably do fine.

[Jayss109]

This book is even better! Both are a must have, Cliff's is put together a little better

http://www.cliffshighperformance.com/buy_book_2.html

or Amazon

Amazon.com: How to Rebuild and Modify Rochester...
Sounds like you need to enlarge the air idle tubes, really helped mine.

J

[highperf4x4]

Just to voice my firm support of the q-jet here's a video of the one I just pulled off the shelf in my storage building where it's been sitting for over 2 years and I slapped it on the 318 in the Satellite. I did nothing but clean the outside of this carb with B-12 and bolt it on guys. You'll see me reach over and force the choke open as I haven't hooked up the electric choke yet. This is the carb I installed the electric choke conversion on by the way and I'll take a pic of it when I hook that back up.

YouTube- New intake and 4bbl for the Satellite