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Thread: Car stops pulling at 2500 RPM

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    Default Car stops pulling at 2500 RPM

    Car is a 71 240Z with a 2.6 from a 260Z. SU carbs are from the 240. The car pulls away and make great power in 1st and 2nd gear until 2500 RPM, 3rd gear it makes power until 2300 RPM. Anything above that and its like someone let off the throttle, its just stops pulling. All plugs are the normal golden brown. Front carbs were slightly rich when I first received the car but I adjusted them. About 1/6 of a turn fixed that problem. Car has the points rebuilt when the engine was dropped in. I thinking it might be a fuel pressure problem but I dont have a gauge. Just though I would query you guys before I go buy a gauge.

    Thanks

    Ryan

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    Semi-retired admin Arne's Avatar
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    Don't rule out ignition problems, especially the coil and any condensers that are on the distributor or coil. I'd actually test that first. Much simpler.
    Arne - Former owner, HLS30-37705, 7/71, 905 Red
    Car blogs - 240Z - Porsche 911

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    Check for loose connections especially around the dizzy and follow Carls advice
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
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    Lots of detail about the engine but only "stops pulling" on the problem. Not much to go on. Does the tachometer needle do anything odd? Does the engine sound different? Do the RPM continue to rise just a much slower rate? How high can you go in RPM?

    Also, you don't say if you have a mechanical or electric fuel pump. The mechanical pumps pump more volume at higher RPM and control pressure through a relief valve. The electric may or may not use a regulator. What do you have?

    And points aren't rebuilt, just replaced, with gap or dwell set when installed. Could be a point gap problem. If the points don't stay open long enough (dwell) you'll get a weak spark. You should probably just do a basic tune-up before buying a gauge.
    1976 280Z, with some minor modifications

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    I will check that Arne, thanks. I was brought up in a fuel injected and now distributor-less world. Carbs are not my forte but I am learning lol.

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    Sounds like fuel starvation to me. Not ruling out ignition but a plugged filter will restrict RPMs under load. A quick check to see if it's lack of fuel, rev the engine, in neutral, to 6000 RPMs, If it happily revs with no load, it's lack of fuel, Another interesting symptom is the car will go the same MPH in any gear & no higher, When it happened to me, all of a sudden the car would not go over 45 MPH. Second, third or fourth gear, 45 MPH. No engine miss, the engine ran fine, My dad was my riding mech. that day & immediately knew what it was, I was able to blow out the filter by the fire wall as a roadside fix, Start with all the fuel filters. Possibly one in front of the tank, another at the fire wall & one on each carb. Fuel pump pressure & volume is next. Hope this helps.

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    Quote Originally Posted by Zed Head View Post
    Lots of detail about the engine but only "stops pulling" on the problem. Not much to go on. Does the tachometer needle do anything odd? Does the engine sound different? Do the RPM continue to rise just a much slower rate? How high can you go in RPM?

    Also, you don't say if you have a mechanical or electric fuel pump. The mechanical pumps pump more volume at higher RPM and control pressure through a relief valve. The electric may or may not use a regulator. What do you have?

    And points aren't rebuilt, just replaced, with gap or dwell set when installed. Could be a point gap problem. If the points don't stay open long enough (dwell) you'll get a weak spark. You should probably just do a basic tune-up before buying a gauge.
    The points were replaced and timing set by my mechanic, not sure if he set the dwell of gap. Car seems to be getting good spark. I had the plugs wires, rotor and cap replaced when the motor was swapped in.

    Feel like a noob here. I can manage to build a 93 Mustang LX coupe and swap a 4.6 4V cobra motor, 6 speed, big brakes, coilovers, hydroboost, and about a billion other things but can't figure out old carb motors. go figure,

    Thanks for the input. Time to learn some old school.

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    Quote Originally Posted by Mark Maras View Post
    Sounds like fuel starvation to me. Not ruling out ignition but a plugged filter will restrict RPMs under load. A quick check to see if it's lack of fuel, rev the engine, in neutral, to 6000 RPMs, If it happily revs with no load, it's lack of fuel, Another interesting symptom is the car will go the same MPH in any gear & no higher, When it happened to me, all of a sudden the car would not go over 45 MPH. Second, third or fourth gear, 45 MPH. No engine miss, the engine ran fine, My dad was my riding mech. that day & immediately knew what it was, I was able to blow out the filter by the fire wall as a roadside fix, Start with all the fuel filters. Possibly one in front of the tank, another at the fire wall & one on each carb. Fuel pump pressure & volume is next. Hope this helps.
    It revs freely to 4500, I will try 6K tomorrow. My personal experience is telling me fuel issues but I also listening to other more experienced carb guys. Friend told me to pull out the choke a little and see if it will rev a little higher.

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    I went through pretty much the same with a 240 I bought a month or so ago. I replaced the distributor and coil with the newer ZX's electronic ignition. It let it go past the 2500 rpm stall, under a load, it would rev up fine sitting in the garage. If you want to rule out fuel starvation, secure a gas jug in front of the radiator. Drill 2 holes in the top and run your fuel lines into the jug, supply and return. I put a shop towel around them then taped it up real good and went for a drive. Still wouldn't go past 2500 on the road.

    get one of these too, https://www.google.com/search?q=clea...w=1280&bih=620
    I put one before the fuel pump and it would cloud up like a glass of tea but the bigger plastic filter caught the crap 1st. Now I'm in the middle of cleaning the tank and replacing fuel lines. Look at these photos, http://www.classiczcars.com/forums/f...ing-story.html
    Last edited by siteunseen; 06-17-2014 at 02:05 AM.
    1972 240Z #918 New Sight Orange
    1977 280Z #305 Light Blue Metallic
    1972 240Z #110 Persimmons Red

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    Looks like it wont rev past 3500 RPM in neutral either.

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    It may be your coil? Mine was low and I could shake it to hear the sloshing of oil.
    1972 240Z #918 New Sight Orange
    1977 280Z #305 Light Blue Metallic
    1972 240Z #110 Persimmons Red

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    Check the wiring inside the distributor. Perhaps when the breaker plate moves from the vacuum advance it is causing a short or open circuit. There should be a small ground wire from the breaker plate to the distributor body. If that is missing or loose it could cause problems. Also, check the wire going from the points to the feed-through on the side of the distributor. Make sure it is not loose, frayed, has insulation worn off, etc.

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    Just a shot in the car because im at soccer with my boys.

    The 76 engine usually has a secondary electric pump. The don't think the 240 chassis has one. Is the secondary pump required and is the mechanical pump on the 260 engine strong enough to meet fuel demands

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    Why the difference in the previous 4500 rpm & the later 3500 rpm. Was the difference caused by creeping the rpms up on the 4500 & stabbing the throttle on the 3500? Also, did pulling on the choke make any difference? Mechanical pumps alone will supply plenty of fuel for round top carbs on a L26 if the filters are maintained.

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    Channeling Occam (actually William - I had to look it up) and Einstein and KISS - are you sure that the throttle blade is opening completely? It's called a throttle for a reason.
    1976 280Z, with some minor modifications

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    Quote Originally Posted by Mark Maras View Post
    Why the difference in the previous 4500 rpm & the later 3500 rpm. Was the difference caused by creeping the rpms up on the 4500 & stabbing the throttle on the 3500? Also, did pulling on the choke make any difference? Mechanical pumps alone will supply plenty of fuel for round top carbs on a L26 if the filters are maintained.
    Typo sorry. Mac rpm is 3500. I did not get to try the choke, we had a bad storm so the Z stayed in the Garage. Fuel filter is new and clear.

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    Quote Originally Posted by Zed Head View Post
    Channeling Occam (actually William - I had to look it up) and Einstein and KISS - are you sure that the throttle blade is opening completely? It's called a throttle for a reason.

    Yes opening completely

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