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Series IIA 109 Rough Idle Misfire Vacuum Leak Troubleshooting

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  • Series IIA 109 Rough Idle Misfire Vacuum Leak Troubleshooting

    Hello Guns and Rovers community, I'm hoping you can help me out. I am new to the series world, and learning as I go. Please see the video below for current running condition, followed by an explanation.

    https://youtube.com/shorts/-w1G8o39K5E?feature=share

    I've been fostering a IIA 109 pickup for my friend Bill Simone's family since his passing 10 years ago. I get it out of the garage every now and then to give it some exercise. For some time now, the truck has been running rich at idle. Fuel mixture screw on the Zenith carburetor changed nothing. Recently, I've been motivated to try and resolve the problem to get this truck running as well as it did 10 years ago. I started with a new carburetor to try and resolve the issue. No change. Idle mixture screw makes no change to how the truck runs. I went through and set valve tappet clearances, and then double checked. I started to suspect ignition problems. The truck is fitted with a rebuilt Lucas 25D from Advanced Distributors with electronic conversation, and a Crane Cams Fireball XR700 Ignition module. I replaced the coil, wires, plugs, cap and rotor arm. Plugs get fouled up pretty quickly because of how rich the engine is running. I've been cleaning them up and checking gap every now and then during this diagnostics journey. Based on the workshop manual, since I'm running 90 octane ethanol free fuel, base timing is supposed to be set to TDC with vacuum advance disconnected, which is where I currently have it set. Compression test shows 120psi in each cylinder. Yesterday, during a test drive, engine speed was increasing while applying the brake peddle. I started to suspect a vacuum leak. This morning, I hooked up a vacuum gauge directly to the intake manifold. Very low and erratic vacuum. I sprayed carb cleaner around the intake manifold in hopes I would find a failing intake gasket. I couldn't get a jump out of the RPMs.

    I'm struggling to determine next steps for troubleshooting. Any help that can be offered would be greatly appreciated.

  • #2
    Welcome Dave! I'm more of a diesel guy now, did you check the vacuum advance on the distributor? Make sure the top and bottom plates turn easily? Also it is easy to get the firing sequence wrong when changing plug wires, the order is on the intake manifold and the rotor turns counter-clockwise. HTH
    gene
    1960 109 w/ 200TDI
    rebuild blog; http://poppageno.blogspot.com/

    You don't see faith healers working in hospitals for the same reason you don't see psychics winning the lottery.

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    • #3
      Do you have a vacuum assist brake booster?

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      • #4
        Originally posted by loose gravel View Post
        Welcome Dave! I'm more of a diesel guy now, did you check the vacuum advance on the distributor? Make sure the top and bottom plates turn easily? Also it is easy to get the firing sequence wrong when changing plug wires, the order is on the intake manifold and the rotor turns counter-clockwise. HTH
        I did not disassemble the distributor yet. I was able to apply vacuum to the line going from carburetor to distributor, and was able to get the rpms to jump, so that seems to be operating fine. I am fairly confidant that the plug wires are in the correct order.

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        • #5
          Originally posted by Paul D View Post
          Do you have a vacuum assist brake booster?
          I do have a vacuum assist brake booster. The video link I included shows the engine running with the vacuum gauge attached to the intake manifold where the brake booster line would normally be connected. However, I thought it was interesting that I was experiencing engine speeds changes during test drives when the brakes were applied. The engine speed would increase noticeably while the brakes were applied. Almost seemed to improve how the engine was idling.

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          • #6
            Could very well be two different issues. You can research the Zenith warp. Basically a quick correction is to use a bit of o ring to plug a hole in the carb body to prevent excess fuel from causing a rich mixture. You also may have a torn vacuum diaphragm in the brake servo causing a massive vacuum leak. You can disconnect the line to the servo and peg it to troubleshoot that aspect.

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            • #7
              Have you tried plugging the intake manifold at the brake booster line? I only suggest it because that's where I had the same issues. The engine ran fine with with the manifold fitting plugged. When I installed a new brake brake booster it started to run poorly. Someone here pointed out a port in the booster that I missed for a sensor used on Series III's. Once I plugged that the engine returned to running fine. Just a thought.

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              • #8
                Originally posted by series guy View Post
                Could very well be two different issues. You can research the Zenith warp. Basically a quick correction is to use a bit of o ring to plug a hole in the carb body to prevent excess fuel from causing a rich mixture. You also may have a torn vacuum diaphragm in the brake servo causing a massive vacuum leak. You can disconnect the line to the servo and peg it to troubleshoot that aspect.
                Series Guy, I'm interested in this topic. Not the first time I've heard discussion about plugging a port in the Zenith. The truck is currently fitted with a new zenith style carb from Atlantic British. Does this port still need to be plugged, or is this referring to original zenith carbs? I applied about 20in of vacuum to the brake booster, and it held solid, so I don't think I have a torn diaphragm, or a leak in the brake booster.

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                • #9
                  Originally posted by Paul D View Post
                  Have you tried plugging the intake manifold at the brake booster line? I only suggest it because that's where I had the same issues. The engine ran fine with with the manifold fitting plugged. When I installed a new brake brake booster it started to run poorly. Someone here pointed out a port in the booster that I missed for a sensor used on Series III's. Once I plugged that the engine returned to running fine. Just a thought.
                  I suspected that as well, but the video shows the engine running with a vacuum gauge attached, removing the brake booster and it's line from the equation.

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                  • #10
                    I'd pull your carb elbow off the top of the carb and see if it runs any better with that off, to eliminate any restriction air restriction upstream of the carb.
                    Pull a plug and check to see how strong the spark is.
                    Try manually adjusting the timing with the engine idling to see if the vacuum pressure stabilizes (if it does, your timing may be off).
                    I'd also bump the idle up a hair.
                    There is nothing more dangerous than those who seek to alter the will of men through force or deception rather than logic.

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                    • #11
                      Timing set to TDC is not optimum. These engines can run 10 or 12 degrees advance without issue. 50wulf’s suggestions were excellent. Carburation and ignition issues are hard to tell apart. Also 120 pounds of compression is low. Maybe check your valve adjustment.

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                      • #12

                        I have pulled the elbow off a few times, and it makes no difference. I have pulled plugs a few times, spark seems good, until they get fouled out fairly quickly from how rich the motor is running. They get dirty quickly. I've also been talking to Jeff from Advanced Distributors. He is suggesting the ignition setup that is currently in the vehicle, which he setup, should be timed to 15 degrees BTDC. I'm planning on adjusting timing, cleaning spark plugs, triple checking valve adjustment, and reporting back.

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                        • #13
                          Dave:
                          I have worked on the 109 with Bill way back when...one of the nicest guys you would ever meet...I would try to advance the timing, I would start at 6 degrees BTDC...drive up a steep hill...keep advancing till it starts to ping. or use the vacuum gauge hooked to the manifold and advance until you get the highest reading...then back off 1 or 2 inches of vacuum. If I remember right Bill installed hardened seats in the head. Once you brought the 109 up to Spruce Cabin and you had the same problem? What happened to the carb that was on the truck to start with... Increase the idle up to 650 or so
                          Live out in Colorado now...tried a copy of the Zenith...might have gotten it to work but I could not get the jets for high altitude...put the Rochester back on...running great...can do 50 going up the canyon roads around Boulder

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                          • #14
                            Cleaning plugs is not a good idea. Once a plug fouls it can’t really be cleaned.

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                            • #15
                              Originally posted by LC Rover View Post
                              Dave:
                              I have worked on the 109 with Bill way back when...one of the nicest guys you would ever meet...I would try to advance the timing, I would start at 6 degrees BTDC...drive up a steep hill...keep advancing till it starts to ping. or use the vacuum gauge hooked to the manifold and advance until you get the highest reading...then back off 1 or 2 inches of vacuum. If I remember right Bill installed hardened seats in the head. Once you brought the 109 up to Spruce Cabin and you had the same problem? What happened to the carb that was on the truck to start with... Increase the idle up to 650 or so
                              Live out in Colorado now...tried a copy of the Zenith...might have gotten it to work but I could not get the jets for high altitude...put the Rochester back on...running great...can do 50 going up the canyon roads around Boulder
                              Larry, correct? Funny story about that trip to the cabin. It seems as though while the gang was all trying to get things to run smoothly, the idle speed screw fell out, so I ended up needing to use the hand throttle to keep the truck from stalling out at idle. Back then, I was still very intimidated by working on this truck. I felt like I was going to do the truck a disservice, since the last person that had wrenched on it was Bill.

                              I've had a recent motivation to get this thing running right again. I still have the carb that was on the truck, which I believe was also a zenith copy. During my troubleshooting, I decided to try a new carb, since the volume mixture screen didn't seem to be doing anything to affect how the engine was running.

                              Is there anything that I should know about hardened seats, and how would would it potentially impact my troubleshooting?

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