Pinking under load!

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John H
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Pinking under load!

Post by John H » Wed Jun 13, 2018 8:52 pm

It appears my car has developed pinking under load. It started on the motorway, at least I first noticed it then. Since then I have found a vacuum leak and a lot of crud in the fuel filter, rechecked the timing 3 times......she is running much better and smoother BUT still pinks! So I am looking at pointers where else to look before I take the carb apart to see if there is residual dirt there.....any ideas would be gratefully received! I did wonder if the distributer advance is working, how can I test that?
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clive
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Re: Pinking under load!

Post by clive » Wed Jun 13, 2018 10:53 pm

Testing the vacuum advance is easy if you have a timing light. I don't have a vacuum advance/retard on my dissy. I can't see how dirty fuel can cause pinking though.
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Re: Pinking under load!

Post by John H » Thu Jun 14, 2018 11:33 am

I assumed it was due to low fuel under load, ie couldn't get enough so ran lean and therefore induced pinking.....same for vacuum leak resulting in low fuel to air mixture.
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clive
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Re: Pinking under load!

Post by clive » Thu Jun 14, 2018 1:07 pm

Pinking (Or pre-ignition) is normally associated with the ignition being too far advanced. Knocking on the other hand is when the ignition is too far retarded. What is your dynamic ignition set to, and did you set it with the vacuum pipe connected?
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John H
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Re: Pinking under load!

Post by John H » Thu Jun 14, 2018 1:31 pm

Roadcraft spec sheet says 15d BTDC, although I have seen a lot of folk set it closer to 10. I set it at 1000rpm without vacuum pipe set. I have tried it at 12D but no noticeable difference . Yes understand the difference Clive thanks.
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clive
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Re: Pinking under load!

Post by clive » Thu Jun 14, 2018 2:32 pm

What is your engine spec? I have the Chilton's Ford Engine Overhaul Manual and it gives various settings dependent on engine.
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Re: Pinking under load!

Post by Karl » Thu Jun 14, 2018 5:13 pm

John, timing at idle is not that important, what harms the engine is is the fully advenced timing with the centrifugal weights fully out. Check the degrees you have there with the vacuum disconnected. You should not see more than 35 degrees BTDC at around 3000 revs. Depending on what you find you can adjust to 32 or 30 and check if you still have pinking. Important is the centrifugal advance must be fully out (max. mechanical advance).
I think you have also the HEI distributor like me. Mine came with different spring sets for the weights. I fitted the weakest springs so fully abvance is at 2700 revs, which made the engine more "lively"! Another thing to check is when the second stage on the carb starts to open. I could see that for sure only on the rolling road. With a Holley, again this can be adjusted with different springs.
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John H
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Re: Pinking under load!

Post by John H » Fri Jun 15, 2018 12:46 pm

Thanks Karl, I was going to PM you about the carb. I found this morning that the engine builder had put the vacuum line to the manifold vacuum so the vacuum advance was engaged all the time. However changing that back and correct I still have pinking. I have checked the full and she is at around 35 BTDC at 3k rpm, which would suggest from your numbers to far. I will pull that back and let you know how I get on. My HEI was fitted by the engine supplier with no additional kit to alter it, I will contact him and see what he has to say.
Thanks John
PS Only a few weeks to LeMans so I need to get this sorted!!
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clive
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Re: Pinking under load!

Post by clive » Fri Jun 15, 2018 3:11 pm

Hi John,

From memory mine is 32 degrees.

CJ
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Re: Pinking under load!

Post by John H » Fri Jun 15, 2018 4:59 pm

So I have set it at 32 now I am waiting for the rain to stop before trying! I will let you know . It does sound different, rougher I would say but the proof will be on the road. Given your description of lively Karl maybe I will wait until the roads are dry too!
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