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Technical Rochester Quad Headache.

Discussion in 'The Hokey Ass Message Board' started by Lungfish, Oct 21, 2019.

  1. Lungfish
    Joined: Aug 15, 2019
    Posts: 11


    Hello all. I need help diagnosing my Rochester Quadrajet. I rebuilt it myself, and it was my first carb rebuild. It's on the 350 block that it came from the factory in, so it has the stock mechanical fuel pump hooked to it. Carb worked, but was rough. When cold, I had to pump the pedal 30 times to start, and then it took a few starts to go. Anyway, I'll try to be brief as possible.

    The carb and block has a divorced choke. I changed it out for an electric one. I don't think that's the issue, but giving that info just in case.

    Bought a rebuild kit from Carbs Unlimited. BUT, when I got the kit, it didn't contain the needle and seat as advertised, it had a valve type of thing that replaced the needle and seat. I decided to use it. Took the carb apart, cleaned it, replaced gaskets, float, needle and seat, adjustment screws, power piston spring etc. Also, I found that the carb didn't have the fuel filter in it. I always run an inline fuel filter, so I wasn't too concerned. But, since I was trying to do it proper, I put a new fuel filter and gasket, etc in the carb (and still kept the inline filter)

    Put it all back together and back in the car. Started it - it kept flooding. Pouring out the top type of flooding. Ok, so I got the float level wrong.

    Took it all apart. Adjusted the float level. Put it all back together. Started right up. Beautiful. Hooked up vacuum gauge. Rock solid steady needle in the green zone. I let it idle for 20 minutes, drove it around the block once. All was cool. Took it on the road later that day and it kept conking out. Had to drive home really slow and pull overt to let it idle on occasion. So, float was too low (I'm assuming).

    Took it all apart again. This time, I ordered a proper actual needle and seat and swapped out the valve thing... long story - I was suspecting it was defective. With the new needle and seat, I adjusted the float to proper measurement with the needle hanging off the metal and not in the hole. Put it all back together and tried starting it. Flooding again... its even puffing fuel mist out of the choke blade.

    So that's where I am. Is there anything besides the float to cause the carb to flood? Can something in the power piston assembly cause it?
  2. squirrel
    Joined: Sep 23, 2004
    Posts: 44,248


    You seem to be ignoring the choke. If the choke is not working properly, it will do all kinds of awful things.

    But the choke acting up won't make the fuel level be wrong.

    I would be looking at the float being saturated with fuel, or the fuel pump being a return type without the return line connected, or something like that. And when you installed the filter in the carb, did you install the spring behind it? if the filter was missing, perhaps the spring was, also.
    carbking likes this.
  3. 2OLD2FAST
    Joined: Feb 3, 2010
    Posts: 1,826

    from illinois

    Did you not like the divorced choke ? You need to do some research about setting the float , the power valve has to function properly and can be a bit fiddly when assembling , I'll bet there's a video or two you could watch or , god Forbid, look in a book ...
  4. BJR
    Joined: Mar 11, 2005
    Posts: 5,992


    "With the new needle and seat, I adjusted the float to proper measurement with the needle hanging off the metal and not in the hole."

    Here is your problem, the needle has to be in the seat when you set the float level.
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  5. carbking
    Joined: Dec 20, 2008
    Posts: 2,586


    Reread the post by Jim (Squirrel).

    Take the carb apart again; and look at the float. Q-Jets come with floats made from 2 different materials - brass, and foam. If brass, test it by submerging in hot water. The hot water will pressurize the air inside the float, and leaks will appear as a stream of bubbles. Replace if necessary. If the float is foam, don't bother trying to test it, just replace it.

    I believe BJR misunderstood your post about the hole. The floats generally have 2 holes in the float arm that look like the hanger should be installed in the hole, and if I read your post correctly, you placed the hanger on the back of the float, which is correct.

    Once back together; ADJUST the choke. The choke butterfly should just touch closed with a cold engine and the ambient at 65 ~ 70 degrees F.

    Now, apply electricity to the electric choke, to get it to open. When the choke is warm, the butterfly should be wide open (vertical).

    Also, as Jim mentioned, there should be a spring behind the internal fuel filter

  6. 302GMC
    Joined: Dec 15, 2005
    Posts: 5,880

    from Idaho

    And test the fuel pressure … any more than 4 1/2 - 5 lbs is not good.
    RMR&C likes this.
  7. s55mercury66
    Joined: Jul 6, 2009
    Posts: 3,746

    from SW Wyoming

    I have had nothing but trouble with the old brass fuel filters, if that is what you have. They always disintegrated on me, and particles would get lodged in the needle and seat, causing the carb to overflow.
  8. 173
    Joined: Feb 12, 2017
    Posts: 6


    Just had a similar problem with a quadrajet on my 318 mopar, took the carb apart several times checking needle and seat, etc. Then I checked the fuel pressure, sure enough it was pumping at 10lbs! I had no idea old mechanical pumps could randomly start producing so much pressure, as the car ran fine a few weeks before. New fuel pump puts out 5 lbs and the car runs great!
    jakespeed63 likes this.
  9. Lungfish
    Joined: Aug 15, 2019
    Posts: 11


    Thank you all for the replies - I did leave some things out for the sake of brevity. I did put a spring in with the new fuel filter.

    I didn't word it well, but Carbking is correct, I hung the needle off the metal edge on not the hole. When I adjusted the float level, the needle was seated in the seat completely.

    As for the divorced choke... when I tried to remove the old one, the bolt broke. This 350 block was a bargain, but it's had its challenges. Anyway, I ordered an electric choke because I had to fabricate a bracket to go over the platform where the old spring mounted, and an 'analog' choke would not have registered the heat properly. I digress . anyway, the choke seems fine. Every time I've started it cold, there has been a tiny opening in the butterfly.

    The float is foam. It's a new one that I installed with the rebuild. I'm assuming it's ok since I've had the thing running, but if I take it apart again, I'll give it a float test just to be curious.

    The 350 block is from a '77 Chevy truck and it's in my '57 Chevy. It was a straight transfer. So the Quadrajet is on the same block with the same fuel pump it left the factory with in '77. No fuel return line, either. The fuel pressure is an interesting theory. I just assumed pressure would drop if a pump was going bad, not increase. I will check that before I take everything apart again.
  10. It sounds like you are approaching this correctly. The floats are a bit hard to adjust til you get the hang of it.
    Kinda have to use two fingers..One to hold the wire pivot/ retainer, and the other to gently push down on the needle.
    If you're satisfied with that, I'd check the pressure, as stated.
    You have an inline filter , so you could replace it with a 3/8 " plastic T and hose to a gauge .
    Start it up and check it at an idle. Then rev it up a little and note that, also. Then shut it off and watch it for a minute.
    Report back. I'm sure we can fix this thing.
    The power piston and the float guide won't cause any issue, unless they are visibly interfering with the float.
    Not likely, unless something is damaged.
  11. squirrel
    Joined: Sep 23, 2004
    Posts: 44,248


    Does the choke open all the way after a minute or two? And stay open?
  12. First things first, have the possible leaks in the main jet wells been repaired, or has the carb body been separated from the base to determine if the carb is leaking internally.
    After it has been sitting for a few days, or at least overnight, before starting the engine, pull off the air cleaner, look into the carb, and work the throttle between closed and full open a couple of times. What you are checking for, is to see if the accelerator pump well has emptied. If you can't see or hear the flow, the problem is that the carb is leaking internally. If you are not sure, get a small bottle with some gas, and pour it in the front vent tube, and try starting the engine. If it starts immediately, this is again a confirmation of an internal leak.

    This is not a complex repair, but it does require patience and care. I have done this to many Qjets, and it has been a solution to the problem in every case. I used the method where I carefully drilled out the bottoms and threaded in short allen screws after coating the threads with JB weld.
    I will post links to how this is done below:

  13. From what I read above, this is a 77 carburetor. Not likely to have well plugs leaking, as those issues were addressed by Rochester.
    Also , being a vapor recovery carb, there is no bowl vent. Unless maybe he can figure out how to pour uphill.
    Carry on...
  14. I didn't see where he had the internally vented carb, but I have had to do at least two 1978 800 cfm Qjets because they were leaking. So GM may have addressed the problem, but that isn't to say that they completely solved it.
  15. He did say it was on the original 77 "block" , but maybe not understanding the lingo , but anyway, I've had a few, make that dozens of the later carbs, and never once have seen the leaking problems.
    But you live in a damp climate, so maybe that explains it.;)
    I'd bet that's not his problem. Ya on?
  17. It's no big deal. The difference could be regional thing. The last two I did looked like this.
    The larger tube at the front behind the accelerator pump is the vent 1978_Qjet_Chev_GMC_.jpg tube I was referring to.
  18. Lungfish
    Joined: Aug 15, 2019
    Posts: 11


    Yes indeed - after a few minutes of running (when it ran) the butterflies were fully vertical.

    I didn't mention it in a previous posts since it slipped my mind, but I had learned about those leak issues, so when I had everything apart, I put JB Weld on it just to be on the safe side.

    My terminology might be off. I just meant that the carb, manifold, and engine block have been together as a unit since it left the factory in '77 and I haven't done any mixing and matching of components. So, despite it not being in a truck anymore, it's still the 'stock setup' which includes the fuel pump that's original to the carb. Which is why I question the fuel pressure theory since the carb and pump have been working together for 40 years. But as was mentioned by one of you, a pump can increase pressure when it's going bad, so the fuel pressure will definitely be checked.

    So a question ... this is the vacuum gauge that I have been using. It's also a fuel pressure gauge, but it doesn't have a return line setup to send fuel into a gas can. Am I overthinking this? Is it just as simple as a T connector and hooking the hose and gauge directly to the fuel line?
    Last edited: Oct 22, 2019
  19. squirrel
    Joined: Sep 23, 2004
    Posts: 44,248


    Does the fuel pump have two or three fittings on it? They used both styles in the 70s, the third line is a return line, and needs to be connected to the return line (to the tank), not blocked off
  20. Lungfish
    Joined: Aug 15, 2019
    Posts: 11


    I meant a return line in the fuel pressure gauge. I saw a few online where they had a tube that ran to a gas can. Wasn't sure if that was common or a rigged up job. Fuel pump just has two fittings. There is no return line in the 57, and wasn't one in the truck it came out of.

    Anyway, I decided to take the carb apart again. This time, I swapped out the new float for the old float which hadn't been adjusted at all (the carb ran rough before the rebuild, but never flooded). It's a foam float, but I did a float test anyway. It was fine. I put it all back together and tried to start it. It floods.

    So, I changed the 40 year old mechanical fuel pump. I figured, what could go wrong. Probably the most rage inducing experience I've had in a long while. I'm an amputee with only one hand, so getting that rod to stay in the block while I held everything together to put it in was a nightmare. Took about six hours of trial and error. I ended up buying thick grease and shoving a blob in there to hold it in place. It did the trick. So, I put it all back together and started it up. It floods... pours out the top.

    So I honestly don't know what is going on. Maybe it's a shoddy rebuild kit? It looks like the correct gasket. What else besides fuel pressure and a faulty needle and seat could cause flooding?

    I'll try to rig up a T thing to check for fuel pressure with the new pump. None of the parts store seem to have them ready to go. I'll probably try Amazon.
  21. squirrel
    Joined: Sep 23, 2004
    Posts: 44,248


    You could have asked about the pump pushrod sooner, we would have gladly told you the trick--there's a short bolt in the front of the block, you can remove it, install a longer bolt just snug, it will hold the pushrod up. Now you know

    If you take pictures and post them, of things that look ok to you, but might or might not be ok, we can take a look. It's really difficult to diagnose things over the internet, without the help of pictures/video/something to let us "look over your shoulder".
    David Gersic likes this.
  22. Driver50x
    Joined: May 5, 2014
    Posts: 38


    If it’s flooding, and assuming the fuel pressure is ok, the problem has to be either the float adjustment or a needle and seat problem. The slightest amount of debris in the needle and seat will cause it to flood. It has to be absolutely clean. Or it could be a defective needle and seat. One tidbit, never ever use pipe thread tape on any automotive fuel line. The tiniest little piece of that stuff in the wrong place will make the needle and seat leak like crazy.
    Last edited: Oct 27, 2019
    Mark Yac likes this.
  23. Lungfish
    Joined: Aug 15, 2019
    Posts: 11


    So an update. I bought a Holley fuel pressure regulator and it leaked badly, so I returned it and got one of those simple Mr Gasket 1-5 adjustable regulators. The carb still flooded, it just took longer to do it, so the regulator seemed to be working.

    I took the carb apart again and removed the new seat. I have some dental cleaning tools, so I used a sharp pointy scraper thingy and cleaned the seat threads in the carb body, gave it a squirt of cleaner and went over it with some Q-Tips. I put the valve thing back in rather than using the needle and seat. Put in the new float and instead of using the paper ruler that comes in the kit, and used a digital caliper for a true measurement. I then put my air hose nozzle into the fuel intake of the carb and gave it a low pressure stream of air and the valve seemed to be ok.

    One thing I did was bend out the C clip that holds the float in place just a wee bit further than normal and let the pressure of the reassembly bend it back to where it needed to be.

    I put it all back together and it fired up and ran great. Drove it around the neighborhood and it would hesitate on occasion, so I removed the fuel pressure regulator and it improved greatly. I've put about 300 miles on it with no problems.

    So I think I solved it. Definitely a learning experience and if I do another one, I'll be more prepared. Big thank you to all of you for the help and shared knowledge. Much appreciated!
    David Gersic, s55mercury66 and RMR&C like this.
  24. Flat Roy
    Joined: Nov 23, 2007
    Posts: 385

    Flat Roy

    Note: If the engine does not start within a minute or and the Key is on, your electric choke will be open thus NO choke.

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