<VV> backfiring through carb on rampy (long)

vair65 at netzero.net vair65 at netzero.net
Mon Oct 1 21:02:55 EDT 2007


Ladies and Gentlemen,
Got some time to work on the rampy again.  To recap, I rebuilt a 110hp engine ('65+) and installed it in the rampside.  I also rebuilt the carbs (late model) at the same time.  This was my first attempt and doing either.  When doing the engine I followed the shop manual and checked all tolerances twice.  The cold adjustment was done on the valves and engine fired up and ran.  After the cam break-in period I attempted to set the idle and sync the carbs.  This is when I discovered that I had a back fire through the carb on the left (drivers) bank.  A hot adjustment was done on the valves to rule out an open valve.  This did help with the backfire through the exhaust but not the carbs.  It was suggested that I do a compression test and the following is the results from a hot test.
cyld #1 - 150psi
cyld #2 - 125psi
cyld #3 - 150psi
cyld #4 - 150psi
cyld #5 - 150 to 155 psi
cyld #6 - 150 to 155 psi
Compression gage is new straight out of box (harbor freight) calibration unknown marked in 5psi increments.  According to Bob Helts book The Classic Corvair the CR should be minimum of 150psi with a maximum 20% range.  I would have to assume this to be on a broke in engine, mine the rings could not be seated yet as I have not been able to break in the engine.
A cyld balance test resulted in about the same reaction on all cylds, the engine would almost die.
What else should I look at?  I do not think this is a carb problem as I switched carbs from side to side and problem remained on the left bank.  I do not think it is a timing issue since it only backfires on the left bank.  Only other possible cause that I can think of is a valve issue, the heads were supposedly rebuilt (looked like they had been gone over to me) when I purchased the engine and rampy.
Thanks for your thoughts.  I might just have to get this thing off to a Tuna Workshop if I cannot figure it out myself with your help.  Yes that is a threat to Terry and Ned, this might be your next project!
Keith Hammett
Willard Mo. 


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