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Old 03-12-2014, 12:54 AM   #1
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Default Low vacuum, engine timing?

I just put my new build all back together and fired it up for the first time. New block, head, pistons, rings, gaskets, bearings, rods, seals, etc. It starts but idles pretty rough and misfires every few seconds. I have checked fuel and spark to be good. I just took it for an easy drive and it will drive, but you can tell it aint happy. Like its hesitating. The main concern is that it is only at 10"Hg at idle and should be in the 16-18" range. So low vacuum at idle. Pretty sure i have checked all vacuum lines to be solid too. The other strange part is that during engine breaking, it still wont go past 10"Hg. I know it used to go up to about 21-22" during engine breaking.

So, i have double checked the timing belt and cam gears (and even have the Flyin' Miata CAM Ninja Tool) and it all looks right by the marks. My question to y'all is does this sound like an engine timing issue? I really cant find a vacuum leak, and wanted some expert opinions before I rip it down again to triple check the timing marks. To me, thats what it sounds like, but wanted some reassurance.
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Old 03-12-2014, 01:11 AM   #2
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Originally Posted by wolfram View Post
So, i have double checked the timing belt and cam gears (and even have the Flyin' Miata CAM Ninja Tool) and it all looks right by the marks.
Forgive us, but I've personally lost count of the number of people who have sworn up and down that their timing marks are correct, only to post pictures and have them be wrong. I won't be the last person in this thread to ask you for a good, high-res shot of the front of the motor with all the timing covers off.
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Old 03-12-2014, 01:15 AM   #3
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yeah, i figured i had that coming. I took the covers off and looked once already, and it seems its as close as i can get it, but i'll go check again. But am i correct in my diagnosis theory? This sounds awfully like engine timing doesnt it?
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Old 03-12-2014, 02:29 AM   #4
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OK. Just moved the intake cam one tooth counter-clockwise and i have a much better idle (like it used to be before the engine build). Now i am still struggling with the 10" vacuum. It idles well at 10" and doesnt ever go past that (even when engine braking). Any ideas? Could i still have a cam timing issue? Ignition timing has been checked at 10deg too.
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Old 03-12-2014, 04:55 AM   #5
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Freaking BOV!!! Think i have it adjusted right now. I am getting about 18" vacuum and idle is steady again. No clue why/how that could have changed. Only thing I can think of is maybe the new rings and head are producing more vacuum now, and it passed the old spring threshold of holding vacuum at idle? Who cares, think its fixed.
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