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Thread: Cold start issues

  1. #1
    757 Traveler Linkstar07's Avatar
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    Default Cold start issues

    As the title implies, I'm recently having trouble starting my car when its cold. It didn't have this problem at all until I performed a compression test and found the #6 cyl to be low at 90#. I found the intake valve wasnt shutting fully due to misadjusted rocker. Adjusted it and now the car takes about 30-45 seconds of cranking to start. If I pull out a spark plug and try to start it, it fires right up. I checked for a good spark and was a little weak so I cleaned all terminals and spark improved but no luck with the starting. I warmed the engine up and adjusted the valves hot and still did not help.(although it ran slightly smoother) I reset and adjusted the carbs with again no luck. It doesnt actually seem to fire until the ignition key is released either. It fires up no problem when engine is fairly warm. Timing is set at 10* initial and 34* total. Starter turns the engine over pretty quickly. I am not seeing the light here. Any suggestions welcome.
    '73 4spd 240z -167741
    '86 Monte Carlo SS 406sbc
    '86.5 Toyota Supra
    '81 Monte Carlo LT1/T56
    '97 GMC Sierra

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    HLS30165540
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    I don't think your problems are related to any recent work that you have done. First off let me ask what type carbs do you have (flat tops or round tops)? Second what type of ignition are you running, stock points or electronic. When was the last time you performed a full tune-up? When were the spark plug cables replaced?
    The 1973 240Z 165540 Slightly modified. L28, 5sp, cam, headers, MSD 6AL, power windows, power door locks, leather seats, custom this and custom that.

  3. #3
    Registered User Walter Moore's Avatar
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    Have you checked to make sure the jets in the SUs are actually moving down when the choke lever is in the ON position?

    It took me about four tries to get that set right when I installed my new carbs from Ztherapy. (But then I had never worked with SUs before...)
    '71 240Z, Because any fool can drive fast in a straight line.

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    757 Traveler Linkstar07's Avatar
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    The carbs are 3 bolt round tops. Replaced the wires a month ago. Plugs look to be in good shape. The dist has been upgraded to electronic by previous owner. I havent messed with the choke/jets that much. But I didnt adjust the choke before or after this started happening.
    '73 4spd 240z -167741
    '86 Monte Carlo SS 406sbc
    '86.5 Toyota Supra
    '81 Monte Carlo LT1/T56
    '97 GMC Sierra

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    757 Traveler Linkstar07's Avatar
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    I tried to start it this evening and it turned over fine but wouldnt start. After letting go of the key, the engine stopped rotating, as you would expect. but when I turned the key to the off position, the engine would rotate a few degrees afterwards with the sound of pressure from the pistons. weird. I also double checked my firing order: it was ok.
    '73 4spd 240z -167741
    '86 Monte Carlo SS 406sbc
    '86.5 Toyota Supra
    '81 Monte Carlo LT1/T56
    '97 GMC Sierra

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    Registered User
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    Assuming you have a strong spark, the symptoms sound like you're not getting "full choke". It's easy to check with an inspection mirror. At full choke you should have about 8mm of nozzle barrel exposed below the adjusting nut (linkage on the side of each carb stroked to or nearly to it's built in stop.) Cables slip out of adjustment easily where they attach to the carb, that's and binding inside the cable are common causes of under choking.

    Because they don't have accelleration pumps (and are side drafts) early SU's need several seconds of cranking when cold to get enough gas into the manifold intake manifold to produce a flammable mixture in the cylinders. It helps (and helps the battery) to crank 3-5 seconds and then wait 5 seconds or so before trying again. Very light, quick pats on the gas pedal while cranking also seem to help sometimes.

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    757 Traveler Linkstar07's Avatar
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    I'll give the choke a try, Dave + Walter. Thanks.
    '73 4spd 240z -167741
    '86 Monte Carlo SS 406sbc
    '86.5 Toyota Supra
    '81 Monte Carlo LT1/T56
    '97 GMC Sierra

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    757 Traveler Linkstar07's Avatar
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    I checked the choke and it was indeed out of adjustment. The console lever moved the carb levers only a little. I adjusted that and got a good deal more range out of it. Still took a LONG time to start it. I checked for proper fuel flow at the carb inlet and got flow. I checked for a spark from the wire coming out of the coil to a ground and it would not fire while the key was in the start position. When I turned the key back to the run position, it would fire a few times. Not sure how the previous owner wired the electronic dist but I believe this to be my problem. I'm going to search how to wire it properly but any tips are still welcome.
    '73 4spd 240z -167741
    '86 Monte Carlo SS 406sbc
    '86.5 Toyota Supra
    '81 Monte Carlo LT1/T56
    '97 GMC Sierra

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    757 Traveler Linkstar07's Avatar
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    I now have no spark at all. My factory manual has no instructions to test the ignition switch. I have a mallory coil that I'm also unsure how to test. It has the spark plug post and two small threaded posts (+ and -) built in. I have power at the + coil post when the key is ON. If anyone knows how to test these I'd appreciate the info.
    '73 4spd 240z -167741
    '86 Monte Carlo SS 406sbc
    '86.5 Toyota Supra
    '81 Monte Carlo LT1/T56
    '97 GMC Sierra

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