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JeffMopar

only running on one carb HELP PLEASE

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    Hello,

    Finally got some time to try to get the Z running. I have the original 3 screws that came on it rebuilt with Ztherepy kits. Got It to start fine and run without the choke after a little warming up. Idles at about 750 to 800. Started to adjust and balance the carbs and realized the rear carb isn't working. I can screw the mixture dial all the way out or in tight and there is no change at all. If I cover the carb with my hand or lift the piston nothing changes. The front carb adjustment works the way it should. I have set the float with the 10 turns down method and verified that the fuel is flowing to that level and stopping at the right height. But cant figure out what could be keeping the fuel from getting into the carb body the way it should!! Any help is appreciated.

    Thank You, Jeff

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    There is fuel in the rear float bowl? Verify visually. If there is fuel in the float bowl then there is a blockage somewhere. Bowl outlet, connector hose or the base of the jet tube...

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    Yes there if fuel in the float bowl. I drained it and did a verification on the fuel height again to make sure it was correct. I am probably going to have to break down and take the carb off and disassemble it again to make sure everything is correct and clean. The car hasn't run since 1990 and I did a complete restoration. This is just working out the little bugs as you go and it gets aggravating. Thanks

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    You could stick the little red straw off a WD-40 can down the overflow bung and see if you can slightly push down on the float.  The float could be stuck?

    The barrel screen on the banjo bolt, where the fuel line is connected on top, could be clogged too.

    Here's a pretty good read talking about cars sitting for awhile.

     

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    I didn't think of the red straw idea. I will try that to see if the float is up. I completely rebuilt the carbs and removed the screens from the banjo bolt when disassembled. The only thing I can think of is that the float is sticking randomly, not all the time.

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    Did you replace the screens in the banjo bolts after rebuilding? They are important...

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    21 minutes ago, Patcon said:

    Did you replace the screens in the banjo bolts after rebuilding? They are important...

    The ZTherapy DVD says pull them off, potential restriction.

    I have one of these before the fuel rail. :)

     Mr Gasket 9747

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    They are not needed if you have a good filter. The fuel in the bowls is totally clean. I installed a filter below the floor pans out of the way and still use the original style so it looks stock. I am going to remove the vent bung tomorrow and check if there is enough room to see inside to verify fuel is entering to keep the bowl full after starting. It fires up very fast with the choke on so I am thinking maybe it is sucking fuel below the level it needs to maintain but the needle is sticking partly and not refilling fast enough.

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      I'm assuming that when you block the carb with your hand, you're feeling a lot of suction. Fuel level appears to be normal in the bowl. Is it possible that the nozzle is staying down in the full choke position even though the choke knob is pushed into the off position? Occasionally, the flat linkage piece that connects the cable to the nozzle needs a bit of a twist to function properly. Try pushing the nozzles up from the bottom with the choke knob off and see if either one will "click" into place. A bit of lithium grease on the sides of the nozzles is a good idea too. Kinda grasping at straws but I've not experienced a carb that does nothing when the piston is lifted.

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    Well I'll be the dissenting voice and offer a completely different theory. I propose that you may be running on one carb only because the butterfly for the other carb is closed. In other words... It's getting fuel to the bowl, but the butterfly is slammed completely shut.

    If that's the case, you can lift the piston and nothing will happen. You could also adjust the nozzle mixtures and nothing will happen. You could hold your hand across the carb face and nothing would happen. A full bowl, and none of it will ever leave the bowl because there's no airflow to pull it out of the nozzle.

    Pulling the choke lever also opens the throttle plate a little and that would explain why yanking the choke makes it run OK while the choke is pulled.

    Did you do any rough sync of the carbs after you installed the carbs and linkage? What happens if you manually push the linkage for the rear carb open a little with your hand?

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    Edit: Dang Capitano Obvious beat me to it while I was downloading fancy pictures. I concur with CO.

    What happens when you Rev the engine rapidly? Does the rear piston lift and the engine respond halfway decent? You may just have the front and rear carbs really out of balance. Throttle blade wise.  Rear throttle blade closed at idle...= no airflow = no fuel draw = no idle difference when piston lifted manually. 

    happens all the time on Triples and happens on SU's as well. Do you have a Carb balancing tool?

    UniSyn_tool_parts.jpg 

     

    Balancer.jpg

     

     

    carb.jpg

    Edited by Chickenman

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    I'll also say that it's a linkage issue?
    Are you watching the ends of the butterfly at the carb body and seeing motion while working the linkage. Like said above - if no suction(air) , no boom


    Sent from my iPhone using Classic Zcar Club mobile

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    Thanx to everyone for the replys.

    Mark, Yes, I have flow in the rear carb and I also made sure the chokes were moving smoothly up and down with the lever. Yes pushed up on jets to verify closed when choke is off.

    Captain Obvious, Chickenman,  Yes I have the Unisyn balancer. Both carbs are adjusted to equal flow. I think that should have to mean the throttle plates are open close to equal. When I rev the engine it revs up fairly smoothly with a little desitation and the pistons move like they should.

    madkaw, I am going to re check the throttle plate movement and make sure the needle and float aren't intermittently sticking shut. I have a few extras to try, it cant hurt, just have to verify float level every change.

     

    Thank you to everyone for the help, I will let you know what I find.                   Jeff

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    11 hours ago, madkaw said:

    Cliff,
    Your not really running that filter are you?


    Sent from my iPhone using Classic Zcar Club mobile

    Yes, without failing.  Ran one on my EFI too, no leaks at 32psi.  I recoated the tanks and wanted to see what was flowing through, no pink gas yet. :D  

    I've never had a problem with those filters.

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    2 hours ago, JeffMopar said:

    Thanx to everyone for the replys.

    Mark, Yes, I have flow in the rear carb and I also made sure the chokes were moving smoothly up and down with the lever. Yes pushed up on jets to verify closed when choke is off.

    Captain Obvious, Chickenman,  Yes I have the Unisyn balancer. Both carbs are adjusted to equal flow. I think that should have to mean the throttle plates are open close to equal. When I rev the engine it revs up fairly smoothly with a little desitation and the pistons move like they should.

    madkaw, I am going to re check the throttle plate movement and make sure the needle and float aren't intermittently sticking shut. I have a few extras to try, it cant hurt, just have to verify float level every change.

     

    Thank you to everyone for the help, I will let you know what I find.                   Jeff

     If the pistons are rising equally, I think the butterflys must be opening. It would seem (IMO) that the problem is in either in the linkage, (doubtful) or it's just a basic "out of sync problem". Have you tried going through the synchronization procedure again? 

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    Quote

    Captain Obvious, Chickenman,  Yes I have the Unisyn balancer. Both carbs are adjusted to equal flow. I think that should have to mean the throttle plates are open close to equal. When I rev the engine it revs up fairly smoothly with a little hesitation and the pistons move like they should.

    " Revs up fairly smoothly and pistons move like they should " ... contradicts the subject line and main premise that the engine is only running on one carb. That tends to lead us all on a wild goose chase??

    Sounds like it's actually running on both carbs, but not properly. Synch them again and check that the pistons are free. Remove both oil dampers. With engine off, lift each piston to the top position and then let it drop. It should move freely with no sticking and should drop freely and stop with a solid " clunk ".

    If there is any binding, remove the Piston cover and make sure jet is centered in jet holder. Check needle to see if it is bent or has score marks. After making any necessary adjustments. Replace the Piston cover and lightly tighten screws. Do the lift and drop test. If any binding, slightly reposition dome cover. There is some assembly variance built in.  Make sure dampers are filled to the correct level with lightweight oil ( I prefer ATF ) and reinstall dampers. Re-synch carbs.

    Edit; Be sure to check for any vacuum leaks around intake manifold. Loose Intake manifold bolts, split hoses etc. A Vacuum leak will put the carb synch out of whack.

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    Just came in from the garage to have lunch. Started from the beginning and adjusted the RPM at full choke to 1450-1500 and made sure the carbs were balanced. Went through the full Syncing and Balancing process again, same results. Felt like no matter what I did the back carb wasn't getting fuel. Pulled the vent bung off to look inside the float body and used the WD-40 straw to push the float down, fuel immediately filled the bowl and overflowed. So I revved the engine to draw down the fuel level but the fuel didn't go down as much as I would think it should. I am going to pop off the choke linkage from the jet when I go back out and check to see if fuel is flowing freely through the hose from the bowl.     Jeff

    Chickenman, you posted just as I was. Pistons are free and moving as they should, needles are not sticking. Checked manifold and carb bolts and sprayed to look for vacuum leak, nothing. Lifting front piston immediately stalls down engine lifting rear does absolutely nothing also covering air flow with my hand doesn't get any response that is why I think there is no fuel flowing as it should.

    Adding a pic in case anybody sees something obviously stupid that I missed.

    Carbs on car (Medium).JPG

    Edited by JeffMopar

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    My interpretation of the problem is "I'm only running on one carb at idle. Above idle, everything seems to be OK, but at idle the rear carb doesn't do anything."  Is that correct?

    What was the throttle position when you synced the carbs? Do you use one of the adjustment screws to raise the RPM's to something above normal idle while you are performing the sync procedure? If that's the case, then your carbs may be perfectly balanced at a higher RPM (wider butterfly opening), but at dead closed idle, your rear butterfly is too far closed for the carb to work.

    Did you manually open the butterfly on just the rear carb with your finger while at idle? What happened? Did the RPMs go up?

    Did you or someone mess with the "do not adjust this" stop screws on the carbs?

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    When you cover the rear carb with your hand does fuel get in the air horn and on your hand?

    Try turning the base idle screw in the rear carb in (the "do not adjust this" screws, as CO calls them) a turn or two.

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    Sorry to ask the obvious but you checked your getting spark on those 3 cylinders?

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    On 3/31/2017 at 8:58 AM, siteunseen said:

    Yes, without failing.  Ran one on my EFI too, no leaks at 32psi.  I recoated the tanks and wanted to see what was flowing through, no pink gas yet. :D  

    I've never had a problem with those filters.

    I'm running the same one too. Mine is about time to be cleaned. Is there something wrong with this design? I was curious what madkaw concern was?

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