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By Daniel Jessup - 5 Years Ago
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Take a look at this video and fire away at your comments. I have never seen one do this before as far as a very small fluctuation between two very close inches of mercury (19 and 20). The vibration is gone from before the carb rebuild, but I wonder what gives? 4 of the 8 plugs I removed were fuel/carbon fouled, the other 4 were just fine. Cylinder #5 does show a much lower exhaust temperature at the manifold exit than all of the other exhaust ports. (used an infrared thermometer) But I don't know if that is because #5 is so close to the radiator cooling fan or what.
https://vimeo.com/331574496
and here is a link to another video I made concerning exhaust temperatures:
https://vimeo.com/331576377
<iframe src="https://player.vimeo.com/video/331576377" width="640" height="360" frameborder="0" allow="autoplay; fullscreen" allowfullscreen></iframe>
<p><a href="https://vimeo.com/331576377">1955 Ford Fairlane 292 Ford Exhaust Port Temperature Readings</a> from <a href="https://vimeo.com/user66981451">Daniel Jessup</a> on <a href="https://vimeo.com">Vimeo</a>.</p>
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By pegleg - 5 Years Ago
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I would suspect that the flutter in the vac gage is caused by an intake valve bouncing or leaking back into the manifold.
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By Cliff - 5 Years Ago
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Hi, Daniel, try a valve adjustment, this was the problem for me in the past, watch for a worn spot on the face of the rocker (dip from the valve stem).
! HE IS RISEN !
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By oldcarmark - 5 Years Ago
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My Vote is for leaking Valve or Valve Adjustment. It looks like the same regular repeating Pattern caused by One Cylinder.
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By Daniel Jessup - 5 Years Ago
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you guys are leading me in the right direction... I checked secondchance garage and they had a nice adobe flash display of different vacuum gauge scenarios. The scenario they showed that came very close to matching my reading was indeed indicating a valve not closing all the way. Almost a valve overlap it said. Which would make sense. When I removed the spark plug from #5, it was the worst, almost 3 times worse, than all of the others. It is the one in the video where the tip had just about "welded" to the electrode. Cylinder 5 was also the one that had the least amount of heat when compared to all other cylinders exhaust temps.
Next time I am in the garage I will take the valve cover off and check #5 intake and see where we are at. I did adjust the valves before I put the engine back in the car, so who knows? I may have adjusted #5 intake too tight... If it is not #5 then I will do a compression check on all cylinders. Last time I did this I was at 155 for all 8, with very little variance from that number. That was some time ago however.
I will let you know how it turns out. Thanks for the advice guys. 
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By MoonShadow - 5 Years Ago
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Look at the tech article by Walt Knuckles. http://www.y-blocksforever.com/tech/html/valvelash.html
He explains a way of adjusting the valves without a feeler gauge. This allows for wear on the valve stem and rockers and gets a truer setting.
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By oldcarmark - 5 Years Ago
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I have used His System several Times. Pretty Accurate.
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By Daniel Jessup - 5 Years Ago
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And you guys were spot on! When has this forum ever failed me?
#5 valve lash on the intake was only .010 and the exhaust valve was OPEN at TDC just a hair. Duh. 
Video to show results on the vacuum gauge!
https://vimeo.com/331877284
thanks again fellas!!!
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