I've recently developed a nasty ping on the highway just trying to maintain speed, it was so bad that I pulled over and retarded the timing on the spot. I still occasionally get the ping but not as bad. here's the thing, if it starts to ping and I step into it enough to get into the secondary's I can overcome it. im irritated because without the extra timing this thing has turned into a slug off the line and it doesn't have that pull at WOT it used to. I pulled some plugs and they are white, fuel filter isn't old, nothings old its a fresh 6000 mile motor. as for the carb its never been rebuilt as far as I can tell, I pulled it off of a 77ish maybe 78 impala wagon in the junk yard. I used it on a buddy's car and it ran fine. I used it on my motor to break the cam in because I knew it worked. the accelerator pump needs replaced (starting to get lazy) I want to rebuild the carb but im in fear its not going to resolve everything.



im not sure where I had the timing set as I just adjusted it for the first week till I found a sweet spot. the car ran fine for about 6 months and over night it developed the issue and the power loss is horrid. could the power valve be the issue by chance?



The engine is a stock 70 350 4bbl HEI with a jm20/22 cam. its my feeling that the lack of fuel is making the combustion chamber hotter than it should be. also it has a 4 row radiator with fresh antifreeze, fresh fan clutch. the car gets used every day so it needs rectified sooner than later. what do you guys think. ive checked for vacuum leaks everywhere I can.

 

Do you have timing numbers at idle and 3000rpm? A carb rebuild is good insurance. Contact Cliff Ruggles, or Everyday Performance for jetting advice and a quality rebuild kit. There are other possibilities, a colder spark plug may help. Since ethanol is added to the fuel now, it requires enrichment across the power curve. Posting the timing numbers would really help.

 

I don't have any timing numbers I originally set it by ear, I also did step down to a cooler plug. I always run 93 octain and have tried booster nothing helps. I'm pretty sure the problem is the carb is calibrated to run conservatively for the late 70s Chevy 350 it came out of and now it's demanding more fuel. I probably just skated by when it was cold over the winter. I'm going to try adjusting the power piston and if that doesn't help I'll change the metering rods. The plugs are white as a ghost, it's obvious it needs more fuel from the primary side I'm just trying to figure out how I am going to do so.

 

Adjust the APT on it, I slot the adjustment post, so I can use a small standard screwdriver. Just count and record the number of turns to remove it. Then slot with a hacksaw blade. Remove the aluminum plug on top and thread the hole where it goes for a removable plug. Then you can adjust while driving. One or two turns out makes a huge difference, either 3 mpg gained, turned down or a big power increase on my 350, two turns out. I am actually surprised it is idiling worth a dam with that cam, most of the late 70's carbs have super lean idle circuits.