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  1. #1
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    Cool Fouling plugs !!!

    Need help with constantly fouling plugs and backfiring . We screwed together a mild 355 stroker about five months ago but can't seem to get the motor running right. Initially thought it was the carb so had that checked over - all ok there (650 Holley DP). Checked the timing -all good set at 16 deg but now find the plugs are fouling after each drive. They were gapped at 60thou from new so I reduced that to 40thou but it's happening again. Under load I cannot accelerate beyond a quarter throttle without it backfiring. The dizzy has been graphed to the cam etc and I'm running an MSD Blaster 2 coil. Help needed!!!!

  2. #2
    Senior Member 2INIL8's Avatar
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    Is the carby jetted correctly?
    What did you check over on the carby?
    Sounds like its super rich.

  3. #3
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    Cool Fouling plugs

    Quote Originally Posted by 2INIL8 View Post
    Is the carby jetted correctly?
    What did you check over on the carby?
    Sounds like its super rich.
    Carby was taken back to factory settings as it was over jetted when I bought it online second hand. I know next time I'll buy new !

  4. #4
    Do you ever leave? Mickss355's Avatar
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    Makes no difference if you buy new Holley - they are jetted for US fuel and 9 out if 10 times they will run lean with our fuel !
    My suggestion is stop fooling around guessing before you damage the motor.
    Take you car to a reputable chassis dyno in your area and have them do a mixture reading and re jet the carbi to the combo !
    By the way 650 dp is too small even for a mild 355 in my opinion.

    I run a 775 race demon which is around the same size as an 850 Holley.
    Last edited by Mickss355; 01-06-2014 at 11:01 PM.
    He who dies with the most toys wins !

  5. #5
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    Cool Fouling plugs

    Quote Originally Posted by Mickss355 View Post
    Makes no difference if you buy new Holley - they are jetted for US fuel and 9 out if 10 times they will run lean with our fuel !
    My suggestion is stop fooling around guessing before you damage the motor.
    Take you car to a reputable chassis dyno in your area and have them do a mixture reading and re jet the carbi to the combo !
    By the way 650 dp is too small even for a mild 355 in my opinion.

    I run a 775 race demon which is around the same size as an 850 Holley.
    Agreed, I've spent too much to break it now. I'll get a dyno tune done and see what happens. Thanks.

  6. #6
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    Cool Fouling plugs !!!

    Quote Originally Posted by 2INIL8 View Post
    Is the carby jetted correctly?
    What did you check over on the carby?
    Sounds like its super rich.
    Some times it's the simple things.....incorrect plugs were supplied! The parts shop was good enough to swap them over as I've bought enough through them. All sorted now.

  7. #7
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    Forgot to mention that the PV was also blown which was overlooked when I took it to be inspected as I bought it second hand. The motor now seems happy and is running as I expected it to from the outset. Pulls hard and feels crisp.

  8. #8
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    how much is a tune worth that you guys have found? hourly rate or overall quote
    I asked for a quote from a place about 2 ks from me and he said $500 straight up with out seeing the car or saying depending on time.
    I thought that was massively steep
    Mine fouls its plugs around the street but on the track its fine so I put a hotter range of plug in for the street
    Last edited by 79vb; 08-07-2014 at 04:47 PM.

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