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69 L71 just dies after a warm idle

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  • Lawrence S.
    Very Frequent User
    • April 1, 1993
    • 801

    69 L71 just dies after a warm idle

    My car starts well cold, drives great does not miss or act up while warming up. Bring it home after a 5 or 10 mile drive and let it idle in the driveway. It idles nice between 750 to 800 rpms and then suddenly just stops running. To get it to start back I push the accelerator pedal to the floor turn the the key fires right back up runs for a while then dies. Sounds like I am losing fuel after the car get up to temp? I have 110 octane no lead fuel in the car now after running 93 10% ethanol with same results. Naturally the car runs better with the 110 octane fuel, but I am not going to be putting that in the car all the time. I checked float levels in the carbs, they check out well. The air fuel ratio is set correctly. Is the fuel pump going bad? Vapor lock? Any suggestions are welcome.

    Thanks

    Lawrence
  • Duke W.
    Beyond Control Poster
    • January 1, 1993
    • 15667

    #2
    Re: 69 L71 just dies after a warm idle

    Sounds like either percolation from the bowls or vapor lock in the pipe to the fuel pump inlet. There are a couple of things you can do. Wire the heat riser valve open, and convert the ported vacuum advance to full time, which will require replacing the OE 15" 201 15 VAC with a 12" B26 (NAPA VC1765 or equivalent in another brand), Use a 1/8" tee to make a new choke vacuum break hose harness with the base of the tee going to the VAC.

    The above will reduce exh. manifold temperature several hundred degrees, which reduces heat rejection to the cooling system and engine compartment.

    One other thing you can do is place insulating sleeves over the fuel pipes, especially the frame pipe to fuel pump inlet, which runs close to the exh. manifolds.

    What you're experiencing is becoming more common. Prolonged idling causes percolation and/or vapor lock, so the first line of defense is to do everything possible to avoid prolonged idling.

    Duke

    Comment

    • Chris H.
      Very Frequent User
      • April 1, 2000
      • 837

      #3
      Re: 69 L71 just dies after a warm idle

      Lawrence, I concur with Duke's recommendations. The VAC swap improved my L71's idle quality 1000%. See thread below.

      https://www.forums.ncrs.org/showthre...226#post806226

      Chris
      1969 Riverside Gold Coupe, L71, 14,000 miles. Top Flight, 2 Star Bowtie.

      Comment

      • Bob W.
        Very Frequent User
        • December 1, 1977
        • 802

        #4
        Re: 69 L71 just dies after a warm idle

        Lawrence, You may want to look at carb insulators from www.HotRodCarbs.com. They have a ad in the March-April 2018 Driveline page 21.

        Comment

        • David B.
          Frequent User
          • April 1, 1988
          • 42

          #5
          Re: 69 L71 just dies after a warm idle

          Lawrence- Based on my own past experience with L71 cars, many times the coil is to blame--especially if it's a 50+- year old original. They work ok until they get warm, then welcome to stallsville! Installing a new repro coil may be the solution to your problem. Dave

          Comment

          • George C.
            Expired
            • April 11, 2010
            • 44

            #6
            Re: 69 L71 just dies after a warm idle

            Lawrence,

            I have been fighting the same problem and I used the DEI product that wraps around the fuel lines closes with velcro. George

            Comment

            • Lawrence S.
              Very Frequent User
              • April 1, 1993
              • 801

              #7
              Re: 69 L71 just dies after a warm idle

              I am going to convert to manifold vacuum and change out the VAC. I changed to manifold vacuum on my 67 L79 and 69 Z with good results. I did not think of doing this on this car for this issue. If that does not help I will then wrap the fuel lines. The coil is not original but a repro of the original, and those can be junk from my experience. I bought a correct repro for my 69 Z and it failed at high rpms so painted a chrome Mallory I had and the car runs great.
              I will report back soon

              Comment

              • Doug M.
                Frequent User
                • January 1, 1991
                • 68

                #8
                Re: 69 L71 just dies after a warm idle

                Worn needle and seat, along with float levels too high in front and rear carbs, will produce your symptoms. Observe carbs, warm with air cleaner off , for fuel "weeping", flooding. Viton needle and seats are good.
                Check to make sure linkage to end carbs is not even slightly binding, causing throttle plates to be slightly cracked, drawing fuel at idle. You can disconnect linkage to end carbs , see if you can create your initial symptom.
                Another way is place hand over front or rear carb when idling ,( there will be a slight air draw as they are designed for that) see if that stalls motor. ( flooding)
                There is a proper procedure for setting the tripower linkage in the 1969 overhaul manual

                Doug

                Comment

                • Lawrence S.
                  Very Frequent User
                  • April 1, 1993
                  • 801

                  #9
                  Re: 69 L71 just dies after a warm idle

                  Originally posted by Doug McClure (18547)
                  Worn needle and seat, along with float levels too high in front and rear carbs, will produce your symptoms. Observe carbs, warm with air cleaner off , for fuel "weeping", flooding. Viton needle and seats are good.
                  Check to make sure linkage to end carbs is not even slightly binding, causing throttle plates to be slightly cracked, drawing fuel at idle. You can disconnect linkage to end carbs , see if you can create your initial symptom.
                  Another way is place hand over front or rear carb when idling ,( there will be a slight air draw as they are designed for that) see if that stalls motor. ( flooding)
                  There is a proper procedure for setting the tripower linkage in the 1969 overhaul manual

                  Doug
                  I checked the float levels but when the car was cold not hot, so will check that too. Also check the linkage. Thanks

                  Comment

                  • Mark E.
                    Extremely Frequent Poster
                    • April 1, 1993
                    • 4536

                    #10
                    Re: 69 L71 just dies after a warm idle

                    Did the car run ok in the past? If yes, before making mods, think through what may have changed or failed to cause this.

                    Timing changed? VAC replaced? Carb changed or adjusted?
                    Vacuum leak? Bad VAC? Weak coil? Weak fuel pump? Spongy or collapsing fuel hose?
                    Mark Edmondson
                    Dallas, Texas
                    Texas Chapter

                    1970 Coupe, Donnybrooke Green, Light Saddle LS5 M20 A31 C60 G81 N37 N40 UA6 U79
                    1993 Coupe, 40th Anniversary, 6-speed, PEG 1, FX3, CD, Bronze Top

                    Comment

                    • Lawrence S.
                      Very Frequent User
                      • April 1, 1993
                      • 801

                      #11
                      Re: 69 L71 just dies after a warm idle

                      Car runs better with the full manifold vacuum and the B26, but still needs tuning. Carbs are now opening up better nice moan but the timing is so far off the car is not pulling like it should with 1025 CFM of fuel being dumped into the engine. I need to go through the car with Duke's timing map and adjust the distributor springs as needed. I think the timing is just too retarded. Lots left in this engine and just not at it's potential.
                      Thanks for the all the help.

                      Comment

                      • Mark E.
                        Extremely Frequent Poster
                        • April 1, 1993
                        • 4536

                        #12
                        Re: 69 L71 just dies after a warm idle

                        What about the stalling issue?
                        Mark Edmondson
                        Dallas, Texas
                        Texas Chapter

                        1970 Coupe, Donnybrooke Green, Light Saddle LS5 M20 A31 C60 G81 N37 N40 UA6 U79
                        1993 Coupe, 40th Anniversary, 6-speed, PEG 1, FX3, CD, Bronze Top

                        Comment

                        • Lawrence S.
                          Very Frequent User
                          • April 1, 1993
                          • 801

                          #13
                          Re: 69 L71 just dies after a warm idle

                          Stalling issue is better. I drove the car to dinner let it sit and it fired right back up and it drove and idled better. The car is idling much higher than previously. I guess because of the full manifold vacuum pulling the vacuum advance? I am going to go through the timing procedures, distributor weights etc. I did this with my 67 L79 and it has never run better.
                          Thanks for all the help guys.

                          Comment

                          • Duke W.
                            Beyond Control Poster
                            • January 1, 1993
                            • 15667

                            #14
                            Re: 69 L71 just dies after a warm idle

                            Converting from ported to full time manifold vacuum will always increase both hot and cold fast idle due to the additional advance. The most efficient idle is with low twenties to low thirties total idle advance, and the higher the valve overlap, the more total idle advance is needed. After converting to full time vacuum advance and setting the initial timing, go through the idle speed/mixture adjustment procedure and adjust the fast idle per the CSM.

                            I think the '69 L-71 has the same centrifugal curve as the '67 version, 30 @ 3800 max. This is pretty aggressive compared to the L-72, which is 30 @ 5000, and to get total WOT advance into the optimum range of 36-40 requires 6-10 initial.

                            Duke

                            Comment

                            • Lawrence S.
                              Very Frequent User
                              • April 1, 1993
                              • 801

                              #15
                              Re: 69 L71 just dies after a warm idle

                              Thanks Duke. I plan on playing with the car today. I will let you know what I figure out.

                              Comment

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