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Backfire cures misfire??


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Cutting a long story short.  I had the cylinder head off to replace stem seals and lap.  All back together and the car ran like a dream.  No more smoke and smooth running.  Did about 20 miles.  Filled up with fuel and she began to run rough.   Good on throttle with occational mis but no idle at all and lots of popping on the overrun.    Suspected fuel issue.  Cleaned jets,checked float etc. Still no idle.  Although timing had been checked I decided to give the dizzy a little turn while it was running and I was holding the throttle open.  Huge backfire through the carb ( a reminder to everybody to always keep your face away from the top of an open carb!!)  Hey presto..problem solved.  I would love to know what anybody thinks it was.  Could it have been a sticky valve after my work on them?  Just glad it is all fine now.

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Part of the long story I missed out was I swapped out all ignition components from my store. It is strange that a tiny turn of the dizzy caused the backfire. The timing was returned to the marked spot at 9 degs. Maybe it was coincidence. Thanks for your input. 

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On strange cures the Ford Capri 3.0 had a strange misfire from new.  FORDS cure was to supply dealers a large mat that was to be placed against the front of the car AGAINST a wall and the car screamed it’s nuts off in first gear for a few mins. it worked every time. 

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I had one of the first Sierras to come off the line as a company car. Constant misfire at 85 mph in top. I asked Ford to check every month for the first 6 months I had it, and at every service afterwards, but they "couldnt replicate the fault" I got used to getting to 85, felt the misfire, lifted off a bit and cruised at about 75 - 80. 3 years later the car went to my local non-ford garage & asked them to check the misfire. 2 days later, I was driving home from work very late around 11pm, pretty tired, on the A2 & was surprised to see blue flashing lights behind me. They informed me I had been clocked for 2 miles at 106. The garage had replaced the HT leads & fixed the misfire without telling me.

3 months ban.

Same  car, couldnt get 1st or 2nd with a cold engine. Ford changed the clutch quadrant, the clutch cable, the clutch plate & cover plate. No better. Eventually they changed the sporty short gear lever for a 2 ft long monstrosity.....but it worked.

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Misfire is back! So having cured itself its back again. Same as before as in running very rough and won't idle. To recap, all ignition parts replaced. Cleaned main jets, air correction jets, idle jet. Checked floats and needle valve. 

Had recently had head off to valve lap and replace oil seals. Car ran very well after that. 

Had just filled up with fuel. Usual BP garage, usual fuel. 

Timing is good. Tried what I did before and twisted the dizzy. No backfire this time. 

Any ideas? 

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