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Thread: Engine refuses to idle

  1. #1

    Engine refuses to idle

    I'm looking for any input from those a bit smarter than me as to what else could be causing an engine to run and rev great but refuse to idle. What I have:
    1600cc engine
    Solex PICT 31 carb that I just tore apart, cleaned and did a basic rebuild
    New plugs and wires
    All vacuum ports plugged
    Distributor timing set and verified plug wires are correct
    I have relentlessly adjusted and reset the idle speed and mixture screws with 0 affect.


    My next steps are to verify spark on each cylinder and then to double check that the jets some how didn't get mixed up before I received the engine. Other than that I have no idea what else to try.


    Thoughts?

  2. #2
    ***Euro-Nova Supporter***
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    have you tried spraying copious amounts of something like wd40 around, particularly around the base of the carb etc to check for any air leaks?

  3. #3
    Senior Member Phill's Avatar
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    if you've ruled out air leaks then re-check the timing. I know you've already set it but it might be worth advancing or retarding it slightly to see if you can improve the idle.
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  4. #4
    Quote Originally Posted by MartinB View Post
    have you tried spraying copious amounts of something like wd40 around, particularly around the base of the carb etc to check for any air leaks?
    I have a number of times with no change in engine speed. I'll repeat with a bit heavier dose of carb cleaner.

    Quote Originally Posted by Phill View Post
    if you've ruled out air leaks then re-check the timing. I know you've already set it but it might be worth advancing or retarding it slightly to see if you can improve the idle.
    I set timing right at 7 degrees and did play with it a bit when it was running with no real change. It's a quick job so I'll recheck it tonight.

    Thanks for the advice guys!

  5. #5
    ***Euro-Nova Supporter*** Peter's Avatar
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    Forget the timing, spark etc.

    Most common and overlooked problem is valve clearance or valve seating. I have a Mercedes Cosworth that hated to start and nothing under 3000rpm and no tick-over, turned out to be valve clearances of zero on all 16. also common problem on the buggys, tight exhaust valve. Ring wear or sticking also produces low compression with the same results.

    Carburettor wise it can only be a blocked pilot jet or drilling. Also check air screw setting.

    It would need a significant air leak to stop it idleing and more likely to cause high idle, a common problem on cars like my E30.which has a lot of vacuum pipes.
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  6. #6
    Thanks Peter! I am going to check the valves and am going to yank the carb back off for a deeper clean.

    An update: Yesterday I was out fumbling with the idle and decided to check the float bowl again after it ran. Thing was empty! Thought perhaps vapor lock caused by the fuel pump flange pinching the rod when it heated up. Made sense to me!

    Pulled the fuel pump flange and lightly sanded down the outside of it (like this). While the carb was back off anyway I yanked the jets back out and blasted them with carb cleaner and followed up with compressed air this time. Reassembled everything and it refused to start... yup, out of gas. Oh well!

    I am not sure if it was vapor lock or I did a terrible job cleaning the carb but after I added gas, slightly played with timing and adjusted the bypass screw out I have idle! A little high, maybe rough but it's step.

    https://youtu.be/B9ec0x1ibvA

  7. #7
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    Nice one, it is so satisfying when you make a break through.

    Dirk

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